Wiring Leap Forward- '73 620 L20B

[Tony620]

Newly acquired, as-is, was idling in the driveway doing systems checks: Headlings Low/High, Turn Signals, Radio, Heater Fan, Electric Pusher Fan, etc.  Does everything work?  What should I look closely at first?  Then, hey wait!  I smell something...  Turned it off.  Well, I put the cart before the horse.  Should've looked closely before trying to use things.

 

The burning I smelled was the fuse box under the dash, 'cause I was sitting in the cab at the time.  But it wasn't limited to there.  The W-R cable from the Alternator melted to the black path leading to the Posi Post.  There's  a fuseable link but not where the diagram says it shoulda been...  Also, scorching ran from the Voltage Regulator connector through the firewall.  No scorching in the Instrument Harness (hurray!) but the Fuse block melted at the Common Circuit entry and exit paths.  So, I think this was the Head Lamp circuit, somehow.  The fuses had been "upgraded" to 20A and 30A from what the diagram says should be 10A and 15A, so that didn't help neither.  Also, I'll post later about the 100A IR Alternator Upgrade. 

 

I really really don't fault the PO here.  It really really was an As-Is purchase and I'm a real novice here so I don't expect to do things perfectly from here on out either.  I'm listing the faults I've found not to criticize the PO but rather to give the community every chance to understand/resolve the underlying issues.

 

Long story short (don't worry, you'll get the long of it down the road) I'm hoping to rewire/refuse/re-relay this pickup to something close to a modern wiring standard, rather than '73 era standard.  I began by attempting a patch job but realized that I'd probably prefer to route as little juice as possible through the firewall.  So, it looks to me like crying time because I have no idea how to re-engineer an engine compartment's wiring..  But dammit, I'm gonna try!

 

Any advice will be much appreciated.  I'm thinking I'd like the following independent circuits with their own Relays and Fuses:  Headlamps, Horns/Parking Lights, Electric Rad Fan.  Is this a job for the Can-Am box, or would that be overkill since I don't have ECU/EFI?  Pictures diagrams of what other folks have done to Rationalize their Engine Harness would be awesome!  Of course, I'll keep scouring other existing threads.

 

I'll post pictures as soon as I'm qualified.  It's a nice little truck.  I'm already feeling pride in ownership, even if I did brick it in the first few hours!

[datzenmike]

Yes the output from the alternator should have a fusible link. But with fuses replased with larger amp ratings I'm afraid nothing can be take for granted now.

 

I'm surprised a 100 amp alternator still uses an external voltage regulator. You'd better explain this alternator and some pictures.

 

There is only ONE BLACK THICK wire carrying power from the battery through the firewall. It goes to the ignition switch as well as to one side of the fuse box for things that are not turned off with the ignition like the brake lights, 4 ways, headlights, interior lamp, clock etc. The ignition switch also sends switched power to the fuse box for radio, wipers, heater fan etc. Once at the fuse box all circuits that come back out through the firewall are fused.

 

CanAm is strictly for wiring EFI it's of no use to you.

[Tony620]

The Alternator is Internally Regulated.  The External Voltage Regular in fact isn't installed at all.  The Connector, though, is there and was jumpered as described in other threads here.   Thanks for clarifying the power flow for me.  Sadly, I'm pretty sure I can't salvage this original fuse box, at least not for the four on the Perma-power circuit.  The other two are fine, though.  I've taken lots of pictures.  Including the hole the Idler Arm Grease fitting wore through the bottom of the Alternator...  I'm downgrading to a 60A IR model for a Subaru Loyale I read about here on Ratsun.  Fits better between the top of the Idler Arm and the bottom of the the Radiator Hose , though I may just need new motor mounts.

 

As far as fuse linking the Alternator Output, haven't I seen mentioned elsewhere that the Alternator Output could just share posts on the Starter?  Would be nice to ride that fat starter cable back to the + post.  Then I could Fuse Link the all the lower current harness wires independent of the Alternator Output.  Could clean up the wiring a bit.  There's a good chance I'm still misunderstanding things, though.

[620slodat]

First, I'm not a wiring guru. I can do wiring, but I have to study things a bit. However, I do have a 1973 620 (my Dad bought it brand new), built in July 1973. It is not running, and the wiring to the motor is not hooked up. Although it is in a tight spot I can get into the drivers door if you need any wiring info, particularly from inside the cab. I'm on here usually a couple times a day, and sometimes during the day also (retired).

 

I see you are from Sps, Washington. The only place I could think of off hand that comes close to Sps is Spokane, but I couldn't think what that second "s" is for. I've been to Spokane several times over many years. My Grandfather lived there for quite a few years before he passed away. A pretty area.

 

Don

Edited July 25, 2020 by 620slodat

[Tony620]

I really appreciate the offer, 620slodat.  Thank you.  "SPS" is my abbreviation for "South Puget Sound".  Not a town, but a region.  Spokane is very nice though too!

[620slodat]

South Puget Sound, very much like the area I live in, although no ocean water here, and as wet from rain.

 

Don

[Stoffregen Motorsports]

On 7/24/2020 at 3:28 PM, Tony620 said:

 

Any advice will be much appreciated.  I'm thinking I'd like the following independent circuits with their own Relays and Fuses:  Headlamps, Horns/Parking Lights, Electric Rad Fan.  Is this a job for the Can-Am box, or would that be overkill since I don't have ECU/EFI?  Pictures diagrams of what other folks have done to Rationalize their Engine Harness would be awesome!  Of course, I'll keep scouring other existing threads.

 

 

My advice - keep it simple.

 

Visual appearance is important to me and seeing a bunch of electrical doo-hickeys installed where original wiring used to be leads me to the conclusion that whoever did the work did not exercise their imagination. If a fusible link was factory, why not use fusible links? Also instead of the store bought relays and holders, if you must install additional relays, get a compact relay/fuse box from someone like Bussmann.

 

The Can-am boxes are cool, and make a complex job seem much easier than it could be, but a well designed custom setup can be much more compact and way more visually appealing. I do like the compact nature of the can am box, but I absolutely loathe the screw post connections. Nothing beats a good supply of Delphi terminals and a w-crimp tool.

 

Buying correct terminals can get tricky, as most supply houses use trade names and searching for something that you don't know the name of can be a royal PITA, but once you figure out the nomenclature, purchasing is much easier. Delphi/Aptiv, TE Connectivity, Deutsch, Hella, Molex, Packard...these are all trade names.

 

And here are some places to buy them -

https://www.newark.com/

http://terminalsupplyco.com/

https://www.mouser.com/

http://vintageconnections.com/

http://www.texasindustrialelectric.com/_packard_terminals.asp

https://www.efihardware.com/

https://prowireusa.com//

https://www.repairconnector.com/products/GM-Single-Wire-Coolant-Temperature-Sender-Connector.html

There's another company name that starts with a "B", but I can't remember...

 

[Stoffregen Motorsports]

https://bmotorsports.com/

 

 

[Tony620]

Wow!  Thanks a lot!  That seems like a "pin-worthy" post to  me...   Considering my current "work truck" theme, the weatherproof connectors certainly appeal to me.  The stock plug/sleeve connectors have not held up well, with a couple plugs actually tearing off when separating them.  The lines from the Engine Harness to the Rear Lighting will simply have to be replaced.  I did the Salt and Vinegar soak which helped a lot but while I have everything out, and since a couple are just kaput, I figure I might as well redo them. 

 

I think for my own sense of accomplishment, though, I'll have to just "get things running" first and maybe revisit several of the spit n polish items.  Let's hope that all things temporary don't become permanent, like the spare tire around my middle!

[wayno]

When I went from a externally regulated alternator to an internally regulated alternator on my 1971 Datsun 521, I connected my alternator output to the starter lug that the battery cable from the battery went to, I see no fusible link in my 521 wiring diagram in that wire, that said when I upgraded to a 1980 Datsun 720 wiring harness I used that wiring harness complete, I did not keep my modified alternator mini harness I had made, the 720 wiring harness does have a fusible link at the positive battery post, I did have to integrate the 720 wiring harness into the 521 components though and that took a while to figure out, actually years to figure out, but the years part was the all the bells and whistles wiring integration, also the round headlights also took some pigtails as the 720 square headlight bulbs are wired differently than the round headlight bulbs, they are not compatible(plug and play).

 

I expect I should mention this, that heavy gauge wire going from the alternator to the starter lug(on my 521 back before the 720 wiring harness conversion) needs to have good solid connector ends on it, the engine shifts around as one drives the vehicle, the wire crimp tools made today are not all the same and up to the task of heavy gauge wires, even though I have an awesome old wire crimp tool that has all the bells and whistles it still isn't really up to the task of the heavy gauge wire needed going from the alternator to the starter lug or battery, imagine if the wire came loose from the starter or alternator and hit a ground source, the whole truck could go up in flames, that wire should actually be soldered on both ends connector to the wire so it can never come loose, also that wire cannot rub on anything as the engine shifts around while driven.

 

Wiring has to be done right, you can see what happens when done wrong, it can actually burn your whole truck and your house to the ground with it, you kinda need to know what you are doing, when wiring the alternator the heavy duty/large gauge output wire goes to the starter lug or to the positive battery cable(starter lug is cleaner), one of the "T" plug wires goes to a keyed source(don't recall which one anymore) and the other "T" plug wire goes to the battery light in the dash which remains wired the same, and there is a large gauge ground wire going from the alternator housing to the inner fender well sheet metal(old external regulator mount hole), that is it, 4 wires.

Also the alternator hitting the idler arm grease fitting is a common issue, see if you can find/use a 1980 Datsun 720 alternator mount, that mount lowers the alternator so it does not hit the upper radiator hose, the 1981/82 720 mount might be the same, I used to make my own alternator mounts but they kept coming loose and breaking, but eventually I found the 720 alt mount brackets, but I have L20b/Z22 blocks in my trucks, not an L16, that block is shorter and may require a custom alternator mount bracket.

 

I do not have any 620 fuse blocks, I only have 521 fuse blocks so I cannot help you there.

[Tony620]

I agree wiring the Alt-Output to the Starter Lug looks clean.  I'm very tempted.  Though I'm very cowardly too, so I might just do direct to Posi-Post via Fusable Link (FL).  The 620 diagram shows the Alt-Out joining the whole harness and all of it going through the FL, but after this meltdown I'm content to keep the Alt-Out on its own FL.  So, two FLs.  I've bought Military Style Battery Lugs, so I can easily put the  big ol' Starter Cable on one side of the Lug and 6 or 7 FLs (or 2) on the other side!  I'm hope to get to it this week.

 

In my frustration with the original hot mess fault, I pulled all the "aftermarket" electrics: Pusher Fan, Pusher Fan Thermostat, Pusher Fan Relay, Push-Button Starter Button, CD Deck, Electric Horn (plastic).  PO included old/spare parts, so I put the Clutch Fan back on until I have more confidence in the wiring situation.  I'd like to get a Puller Fan with a snazzy hose-mounted relay I've seen folks do on Ratsun.  LED the whole sucker would be boss too.  Gotta stop getting ahead of myself..

[Stoffregen Motorsports]

22 hours ago, wayno said:

also the round headlights also took some pigtails as the 720 square headlight bulbs are wired differently than the round headlight bulbs, they are not compatible(plug and play).

 

I expect I should mention this, that heavy gauge wire going from the alternator to the starter lug(on my 521 back before the 720 wiring harness conversion) needs to have good solid connector ends on it, the engine shifts around as one drives the vehicle, the wire crimp tools made today are not all the same and up to the task of heavy gauge wires, even though I have an awesome old wire crimp tool that has all the bells and whistles it still isn't really up to the task of the heavy gauge wire needed going from the alternator to the starter lug or battery, imagine if the wire came loose from the starter or alternator and hit a ground source, the whole truck could go up in flames, that wire should actually be soldered on both ends connector to the wire so it can never come loose, also that wire cannot rub on anything as the engine shifts around while driven.

 

Wiring has to be done right, you can see what happens when done wrong, it can actually burn your whole truck and your house to the ground with it,

If you search the web for "headlight wiring" you get many different results as to how the headlight pigtail is wired. The headlights in my Rover weren't functioning properly so I had to troubleshoot them and ultimately found that the wires were going to the wrong terminals on the headlamps.

 

Your statement about burning to the ground, that's what fusible links are for. A properly sized fusible link will be four sizes smaller than the wire it protects, so if the main alternator power is 6 gauge, then the fusible link should be 10 gauge. I don't solder them anymore as solder can actually weaken the connection by making it brittle over time. I use a good hydraulic hex crimp tool for anything larger than 10 gauge, and wrap it with good heat shrink, sometimes even double up on the heat shrink.

 

Over time, many owners have modified their wiring, and often they tap into a wire not understanding about fuses. I recently subbed out a sound system install to a local car audio shop because my work load was more than I could handle. When I got it back, I noticed that they tapped into the main fusebox power on the wire BEFORE the fuse box, ie- un-fused. I also made a similar mistake myself a couple years ago on the Jeep CJ5 I auctioned off. I wired the reverse light switch without a fuse (I tapped into another wire for its power), and when I got the Jeep back from the exhaust shop, the wire was draping down touching the exhaust. Well, it burnt through the insulation and grounded the wire and the whole circuit went up in smoke. I had to completely unwrap the rear body harness and replace the entire wire. A simple mistake took almost 5 hours to fix.

[Tony620]

Is there some Best Practice reason to Ground the Alternator through the Chassis, rather than through the Engine?

 

I had a thought.  Tell me if I'm way out of line here.  But can't I ground the Alternator via the Engine Strap?  Or is it Best Practice to do it to the Chassis (Passenger Side Firewall) instead?  My Voltage Regulator plug is toast and I'm using an Internally Regulated Alt now, so I'm taking the 12AWG WR straight to the Battery via Fusable Link. I've spliced the small gauge W wire from the Ignition to the small gauge Y from the Alt T plug (Sense Circuit).  I've also spliced the small gauge WR (Alt Dash Lamp) and the small WB from the Alt together (Lamp Circuit).  Now the melted Voltage Regulator Connector does nothing for me.  So I'm planning to Ground the Head and Tail Lamps circuit to the Chassis using one of the VR Mount Points.  Would be nice not to have to run a 12 AWG Ground Line from the Alt all way to that same point (which seems most "Stock") to ride the Chassis Strap.

 

Boy, this will be easier once I'm Frocked enough to post Photos 😉

[wayno]

It's already grounded to the block via the mount and so was the externally regulated alternator, but all Datsun/Nissan alternators have that ground wire going to the body sheet metal, firewall, inner fender, I see no difference between the two choices, they are the same, I only suggested the regulator mount hole as the wire is already there in the wiring harness, so that is an easy decision for me.

 

For me when I did the alternator upgrade I could not do it by jumping the external regulator plug wires as it would not work properly(I tried), so I made my own mini wire harness for the internally regulated alternator and only used the dash light wire and everything worked fine using my 521 wiring harness, when I upgraded to the 1980 Datsun 720 wiring harness the alternator was plug and play.

[Tony620]

Thanks Wayno!  In my case, the Ground Wire from the Alternator melted into an amalgamated block with the Output Wire, the T plug wires, the Oil Pressure Sensor Wire, and several others once they joined the trunk...  So, I'm free to Ground the Alt anywhere, I guess.  I'll use the Engine Strap and report back once it's up and running (ETA ??).

[DanielC]

I do not know if you are using an internally or externally regulated alternator.   There are two ground wires that need to go to the alternator.   The following info is based on a 521, but I think the grounds are the same. 

The battery negative cable, the big thick one goes from the battery negative to a connection on the cylinder head,  just behind the fuel pump.   There may be a lifting lug there, but after more than four decades of previous owners, the lug could be gone.  There is a ground wire from the head attachment of the negative cable to the alternator frame.

 

From the alternator frame to the voltage regulator base, on the inner fender there is another ground wire. 

This wire is necessary.  It grounds the cab.  If this wire is missing, or loses a good connection, the cab will ground through the throttle cable,  the throttle cable cannot carry this current, it gets hot, and melts the plastic cable housing, and this sticks the throttle at whatever opening it is.  

 

Not on a stock 521 but I recommend you put a short wire jumper around one rubber engine mount, connecting the engine block to the frame of the truck.  This grounds the frame of the truck.  

Ground the bed to the frame.  

On a 521, the tail light assembly has a ground wire from the individual lamps to the tail light frame, and the frame is intended to ground to the bed.  I run an additional wire from the tail light frame to the frame of the truck.

[Stoffregen Motorsports]

2 hours ago, DanielC said:

 

Not on a stock 521 but I recommend you put a short wire jumper around one rubber engine mount, connecting the engine block to the frame of the truck.  This grounds the frame of the truck.  

Ground the bed to the frame.  

On a 521, the tail light assembly has a ground wire from the individual lamps to the tail light frame, and the frame is intended to ground to the bed.  I run an additional wire from the tail light frame to the frame of the truck.

Yes, this is good advice.

 

I use battery cable to ground the engine to the battery, but smaller wire (6-10 ga) can be used to ground the frame to the engine, the body to the battery, etc. Sometimes I use battery cable to the frame and then at the same point, make a short cable from there to the engine block. There are double ended battery cable lugs if you want a single connection.

 

 

I even run a small ground wire to the radiator to prevent electrolysis.

 

 

[Tony620]

Thank you Daniel C and Stoffregen!  I plan to follow your advice and use several grounds.  The battery cable (4 AWG) is grounded to a lifting lug on the side of the engine block.  The alternator is grounded to the chassis with a 12 AWG wire where the External Voltage Regulator used to mount.  a few inches away from there another 4 AWG cable connects the Chassis to the Battery.  I hadn't considered the Radiator or the frame, so I'll work those in too.  I'll use 12 AWG for the Radiator since it's the largest I have on hand.   Why not Bed to Frame, Bed to Chassis, Chassis to Frame too?  I'm guessing they all ground fine through their respective mounting bolts, though.

[Stoffregen Motorsports]

To clarify, the frame is part of the chassis. A chassis consists of suspension and frame.

 

So yes, bed to frame, body (cab) to frame, frame to engine, engine to body. The battery should also have a main ground direct to body and most wiring harness' have a main ground at or near the battery too.

[Tony620]

PO bypassed the headlamp switch, using two separate Toggles mounted on the aftermarket center console.  Examining the factory Switch and the Fuse Block, I'm guessing this was subsequent to a prior issue where the headlamp circuit overheated damaging them both.  I tested the switch with a multimeter last night and confirmed that the Headlamp stage was inop.  There was a little minor melt on the switch wire for that stage and the slightest heat stress on the black insulator of the switch itself.  Dissecting further revealed that the points on the headlamp side of the switch were heavily corroded with the dreaded blue green scale.  A quick brushing and they look as good as new.  I reassembled the switch and now it tests out fine.  I had a similar failure in my '84 720 circa 1995 and a similarly clumsy workaround (back then I put in a dash-mounted toggle).  This wire brush refurb seems more elegant a fix and I hope it will get me another 10 years or more out of it. 

Edited August 12, 2020 by Tony620
Removing Links, Adding Images

[Tony620]

Changed prior from Links to actual photos.

Edited August 12, 2020 by Tony620

[Tony620]

Speaking of switches..  neither the Acc nor Start stages test out on  my Ignition Switch.  Anybody ever repair these?  It's a Niles part and I'd hate to replace it if I don't have to.  I'm not seeing an easy way to open it up to check the internal electrics, though.  If it can't be fixed, I'll just go with a push button for start and forget Acc for now.  I reckon, though, that since the Acc and Start stages are dead the On stage may not be far behind...

[Stoffregen Motorsports]

I believe you can buy just the switch portion of the ignition switch, ie- no key tumbler included.

 

It is possible to take them apart, but they can break during that process.

[Tony620]

Thanks.  looks like the Beck Arnley 201-1174 is what you're describing, available for ~$20.  Not sure, though, how to mate it with the front half (tumblers) from my current switch.  I'll post if I figure out anything useful.

[Tony620]

On 8/5/2020 at 10:26 AM, Tony620 said:

Thanks.  looks like the Beck Arnley 201-1174 is what you're describing, available for ~$20.  Not sure, though, how to mate it with the front half (tumblers) from my current switch.  I'll post if I figure out anything useful.

Well I haven't learned anything on the replacement ignition switch but at least I learned that my stock switch wasn't actually broken.  Instead, the BY wire was mostly severed for some reason, likely giving the PO the impression it the switch was flaky in the Start position.  As far as the rest of my wiring project, I think I'm ready to connect everything back up now.  I'm doing it in stages, though.  Tonight I got as far as turning the starter over.  I was kinda hoping for combustion but not completely surprised it didn't start; it's been dry since the harness smoked back in early June.  Tomorrow night I'll do more thorough checks before I despair over no combustion.  Thanks again to everyone. This forum has been invaluable.