Introduction & Electrical Mess - 1984 720 King Cab 4x4

[dustinsandwich]

Hi guys. New to the forum here, but I think I'm gonna be a frequent visitor.

 

I'm sitting here at the dmv, waiting to transfer the title and get new tags on my new 1984 Datsun/nissan 720, amd I thought I'd make a post saying hello and asking for advice.

 

So someone has done the works to my truck, and they seem to have been a competent mechanic but absolute shit electrician. I've got a random splice out of the wiring harness near the front right headlight thats been left cut, a jumped cable at the fuse box, a 25 amp fuse in there (pretty sure there's no 25 amp accessory on this truck). There's the obligatory aftermarket radio installed that works intermittently, and an LED fog light that someone started to wire and seems to have given up on.

 

I doubt the amateur electrician knew that the 720 harness works by supplying ground to powered circuits. I'm still figuring this out, I think the relays operate as on/of switches and basic logic gates by controlling ground shunting to specific devices. Do I have that right?

 

Anyway, Things that don't work: cabin light (found some cut wires on either side, might be the absent defogger or the light, haven't tested yet)

All dash lights except for the oil and parking brake which are constanly on, and turn signal indicators.

The heater/ac. Blows nothing does nothing.

Horn.

Passenger side turn signals, high beams, brake light.

Seems there's a constant draw somewhere, I've been pulling the battery terminal over night.

Parking brake cable is missing, I have to replace the front (I think) cable.

Speedo and tach are flat, the cable is not hooked up but does exist so at least the hole in the case it goes to is not open to the road.

 

Things that do work: fuel pump, fan, drivers side indicators and high beams, wipers, starter, alternator, oil pressure and volt gauges, low beams (discovered they worked after driving around and messing with the unlabeled stalk until they popped on, seems the flash to pass was stuck on)

 

Weird stuff: bridging the splice got me parking lighs on both sides but no stop or turn signals on the passenger side, and the heater control illuminator lamp in the cab. The splice seems to be two GY to a black, which I think is ground. I can't find an 84 wiring diagram and the resolution is too bad to see what GY goes to on the 82 FSM PDF I found. I have an 84 FSM in the mail. Any clue on this?

 

Just collecting my thoughts and asking if anyone just by chance knows exactly what's going on here from my description. I appreciate any help!

 

I'll post pics once I'm out of the DMV. 

[dustinsandwich]

Okay, I just went to change out and test the fuses and one of the relays on the fuse block is hot to the touch. I'm guessing this is the headlight relay.

 

It's the forwardmost relay or farthest to the right if facing the fuse block.

Edited September 24 by dustinsandwich
Added info

[dustinsandwich]

The fuse block back 

one of the offending wires

Where it leads. Appears to be the same orange/brown

the second suspect. Larger gauge red wire spliced to black and then to another red large gauge red. 

 

You can also see a large gauge red spliced to a RG wire. I haven't traced this. I'm afraid I'll have to pull the dash to figure out what mad nonsense is going on here.

[datzenmike]

Well I have to start somewhere...

 

If you don't have one get a 12v test light. Check all fuses for power. 1 through 5 are on with ignition. 6 and 7 are accessory. 8 through 13 are hot at all times. 14 and 15 are also hot at all times.

 

Headlights:

The last two fuses on the far right are for the headlights. 10 amp each. Should have 12v on both contacts

The far right is for the right side hi/low lamps

The second from the right is for the left side hi/low lamps.

When the headlamp switch is pulled out, power from these fuses goes to ALL the right and ALL the left lamps.

The headlight relay grounds the appropriate hi or low lamps selected by the dimmer switch.

There are only two relay choices hi (relay off) or low (relay on). The headlamp relay is powered by the parking lights. No parking lights, the relay remains off and the hi beams remain on. The relay might get warm but shouldn't be hot. See if someone has tried to wire fog lights and remove anything not stock. Tape up anything exposed.

 

Heater:

The 10th fuse over from the left is for the heater. It's the only 20 amp fuse so replace it with the correct one. It's the red wire that's been cut and another wire spliced into it. Find the other end of the red wire, it should go the the heater relay located just to the left of the headlight relay, and find out why they cut this. 

 

 

 

Radio:

 

 

The second splice (right) is into the radio fuse. Find the other cut end and get it connected back up.

[dustinsandwich]

36 minutes ago, datzenmike said:

See if someone has tried to wire fog lights and remove anything not stock.

Someone definitely did i just found a black wire running from the negative terminal cut.

As well as this cut

The left is a splice into two GL wires, the right is a splice into one RY wire.

 

There's also a fresh loom grounded to the chassis under the wiper reservoir. It's not hooked up to anything in the engine bay except that ground, but it leads into the cab.

 

Testing the fuse contacts now.

[dustinsandwich]

Rightmost fuse: 10 amp tests good. 12.3 volts at contacts with lights on. Fuse replaced. No change with brights. One of the relays started buzzing with this bridged and the lights on, could this be a headlight left on warning? It stopped when I dropped the multimeter leads in surprise, didn't come back on when I replaced the fuse.

 

Second from right fuse: 10 amp tests good 11.4 volts at contacts with lights on, drops to 10.8 with brights on. Fuse replaced.

 

No read from test light on inner passenger headlight. Then my battery died.

[dustinsandwich]

Okay, GL wires are both horns. They connect and route to plug 92M (connects to horn relay), then route through a G wire to 5th fuse, which routes out through a W to fuseable link 23M into positive battery  terminal and grounds at the negative.

 

Page EL-83

[dustinsandwich]

RY might be heater blower motor page HA-10

[Thomas Perkins]

By the way,you have the wrong battery in your 720.Here is mine.

[dustinsandwich]

Thanks, added to the list. Guess I have a donor for my electrolysis experiments.

[NC85ST]

If the battery fits and does the job, don’t worry about it. You have 150 cca’s more than Tommy’s, 850 for yours, 700 for his.

[dustinsandwich]

3 hours ago, NC85ST said:

If the battery fits and does the job, don’t worry about it. You have 150 cca’s more than Tommy’s, 850 for yours, 700 for his.

Roger, thanks. 

[EDM620]

I'll attach a quick diagram of the 720 fuse block and what should be there on another post (it's on a different laptop). The max factory fuse is 20amp.

 

 

[Thomas Perkins]

Only need 700 cca.Been using this type for 30 years.Dont get cold in Georgia.Still the wrong battery.

Edited Thursday at 12:49 AM by Thomas Perkins

[dustinsandwich]

Thanks fellas.

 

I got some time today and did the torquing of the head bolts. Not too bad, only took an hour or so once I got going.

 

Then I pulled the dash, and boy did someone with some ideas have their hands in this harness. Like an archeologist in a Lovecraft story, I've uncovered the work of at least two bizarre minds. It's hard to tell what's meant to be spliced and what's been taped up well from factory.

 

Did Nissan use insulation tape at all, or was it all the riged insulated tubing?

 

 

In particular this coming off the main loom behind the passenger headlight. I'm almost certain the cut wire corresponds below it but then I've got three, amd it looks like there's some other connection before that.

 

Also, the headlights were in the wrong order on that side. Had to switch them around.

 

Tested the turn signal, only had continuity on one post to ground at the plug. Not sure if that implies a dead bulb, though they both look good. I couldn't get the bulb out for rust. Horn and extra light connectors look stock but are non-functional.

 

I lost light and spirit before I got to rewiring the fuse block cuts and tracking down the heater wire. Blower is non-functional, red wire leads under the steering wheel in what appears to be a non-factory routing.

[dustinsandwich]

Here's the back of the dash, if anyone is interested 

 

[NC85ST]

All of those wires were cut? Wow! You’re going to have fun. At least you’ll know your trucks wiring inside and out when you’re finished.

[Thomas Perkins]

That looks scary.

[EDM620]

Attached is what the stock fuse box should be. Diagram defines:

 

Output to factory circuit | Wire Color | Fuse location # | Fuse | Wire colors | Input source

 

Fuse position #9 was left empty/blank and can be used as a power source for anything you want an always HOT source

If your truck had AC or other options, there may be differences.

 

Attached to your fuse block should be 2 relays, 1 Black & 1 Blue. The Black is the heater relay, the Blue is the headlight relay.

Again if your truck had AC etc, there may be additional relays attached to the fuse block.

[EDM620]

Those wires that were cut are most likely aftermarket stereo butchering. The taped wire with connector and the ring should have been cigarette lighter. The twisted pair most likely factory speakers (left and right). At least the wires to the instruments appear intact.

[dustinsandwich]

14 minutes ago, EDM620 said:

Attached is what the stock fuse box should be. Diagram defines:

 

Output to factory circuit | Wire Color | Fuse location # | Fuse | Wire colors | Input source

 

Fuse position #9 was left empty/blank and can be used as a power source for anything you want an always HOT source

If your truck had AC or other options, there may be differences.

 

Attached to your fuse block should be 2 relays, 1 Black & 1 Blue. The Black is the heater relay, the Blue is the headlight relay.

Again if your truck had AC etc, there may be additional relays attached to the fuse block.

This is fantastic, thank you.

 

14 minutes ago, EDM620 said:

Attached to your fuse block should be 2 relays, 1 Black & 1 Blue. The Black is the heater relay, the Blue is the headlight relay.

I've got two black relays, is it possible someone put a hearer relay in the headlight socket, or are they keyed so it wouldn't fit?

[dustinsandwich]

10 minutes ago, EDM620 said:

Those wires that were cut are most likely aftermarket stereo butchering. The taped wire with connector and the ring should have been cigarette lighter. The twisted pair most likely factory speakers (left and right). At least the wires to the instruments appear intact.

Awesome, thanks. I taped the cigarette lighter and dimmer to keep track of them and get them out of the way. 

 

I think there has been at least two aftermarket stereos wired in here, I pulled one that was wired in with hopes and prayers instead of crimps.

[dustinsandwich]

2 hours ago, NC85ST said:

All of those wires were cut? Wow! You’re going to have fun. At least you’ll know your trucks wiring inside and out when you’re finished.

Yeah, I'm learning a ton already. I'm planing on putting a completely independent fuse block on for aftermarket accessories after returning the wiring to stock to avoid this mess in the future.

[wayno]

My advice is you put the headlight circuit back together using the colored wires(connect red/white line, ect.), same with dash wiring, that headlight circuit is a stand alone circuit, if any wires are added to it that make a ground connection it totally messes up that circuit, at night one can sometimes look real close at the headlights and see they are barely on which drains the battery, even adding an aftermarket gauge light/radio light to the circuit introduces a ground and messes everything up.

 

I have learned this from using 720 wiring harnesses in older Datsuns, round headlights are wired differently than square headlights, all lights in 720 dash lights have 2 wires(no black ground wire), the dash lights themselves go to a switch that makes the light dimmable, I believe that is where the ground is introduced and is why all dash lights have 2 colored wires(not black).

 

One cannot introduce grounds in either the headlight circuit or the dash light circuits, the front side marker lights might be the only exception.

[dustinsandwich]

5 hours ago, wayno said:

My advice is you put the headlight circuit back together using the colored wires(connect red/white line, ect.)

That's my plan, the only problem I have is the first electrician made some splices that don't make sense to me. There are two green/blue wires that might go together, but I'm not sure because they both come from the some side of the loom, and then a red/yellow which has a splice into it.

i don't know where these are supposed to go, though when i bridged them the running lights came on.