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Wiring Leap Forward- '73 620 L20B


Tony620

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I'd be interested to know about the 720 outboard idler.  I'm not up to any fabrication for the time being.  But I am replacing this 100A with a 60A for a Subaru Loyale.  It's smaller than the 100A but still larger than the stock 35A and the current size belt has it pinned against the radiator hose at the water inlet.  I'm thinking a longer belt could help.  I'm also curious whether my engine mounts are too wore out; whether newer mounts would get me more clearance above the Idler Arm.  I'm sure I can get it running for now but I'm worried about conducting heat from the water inlet, as well as having that hose split directly over the alternator...

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Here's something: Looks like the PO followed this tech article to use an aftermarket Relay for the Head Lamp circuit.  It recommends using R for both the Power (30) and Signal (85) source.  

1200 Tech Wiki 620 Headlight Wiring

Anybody else try this?  It's breaking my brain.  Using R as both the Power and the Relay Signal, I'm not understanding how the Low Beam (RB)  Circuit ever gets powered.  It looks like only the High Beam (RW) Circuit is ever powered, then modulated between high or lower power states via the Dimmer switch.  If that's so: 1) how does RB ever get powered? and 2) how does RW perform in the low power state of the Dimmer switch?

RelayHeadlamp_1.jpg

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Your reinventing the wheel on the outboard idler, it's not worth the effort when there are easier alternatives.

Try to find an alternator mount for a Datsun 720 with a Z22 engine, they have the large alternator and it fits without hitting the hose above it as the holes are higher in the bracket therefore mounting the alternator lower.

Here are two L20b alternator mounts, the first has the alternator mounted high, it is mounted above all the bolts, the second one has it mounted below the two upper bolts, it's likely more than an inch lower, therefore the alternator would be over an inch lower.

006.JPG

DSCN3508.JPG

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That explains it!  I was wondering where my alternator mount came from!  Looks like I've already got the 720 mount.  I bet the PO was a Ratsuner!   Now I understand why this alternator is hitting the Water Inlet and why the old (bigger) one was bumping the Idler.  I think I have plenty clearance over the idler with this smaller Alt; I might test fit a longer belt just to move it a but lower away from the water inlet.

AltBracket_1.jpg

AltBracket_2.jpg

AltBracket_3.jpg

Edited by Tony620
Typo, changed the meaning.
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You have the one that positions the alternator high, so you have to use a longer belt and that puts it closer to the idler arm, one day instead of poking a hole in the alternator it will break the front bolt holding the alternator on, and that is a bitch getting that fixed, you have to remove the mount and get the broken piece out of the mount and then put it all back together just to repeat fixing it again in less than a year, well that is how it was for me, but I have a very heavy Datsun 521 truck and pull a trailer, I haul weight so the engine moves around a lot in the engine compartment.

I made several custom mounts that worked alright till they broke, finally I figured out to use the Z22 alternator mount and have not had to fix it in several years now.

 

I would not worry about the coolant outlet as long as the alternator is not hitting it/rubbing against it, them hoses above hardly ever spring a leak, and more water gets on the alternator driving thru a puddle than that hose ever would. 

Edited by wayno
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Putting in the effort to ensure good grounds to body & frame will go a long way to preventing future electrical gremlins, as the majority of those stem from bad grounds. Do consider running a separate add-on fuse box if you want to add other things like a killer stereo or whatever.

 

I'm upgrading to a 720 wiring harness on my build (for a different reason) and removing circuits that I don't/won't need. Like Stoffregen I prefer my wiring to be neat & tidy, this also helps to eliminate future issues. I will have my original 620 wiring harness available complete minus the fuse box cover, if anyone is interested.

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First, I have a 1973 620, made in June or July of that year (not taking the time to go out and check).My Dad bought it brand new,so I know the history.

 

It's been a couple years since I compared the 620 and 720 idler arms. Using my memory (not always accurate), the idler arms for the 620 and 720 have different bolt patterns. So if substituting the 720 arm for the 620 arm, at minimum, re-drilling one, or more, holes would be needed. Also, the 720 arm is on the outside of the frame where the 620 arm is on the inside, which might cause problems with the steering. Before I got a 720 frame I was looking at swapping the 620 tie rod with a 720 tie rod. At minimum the swap would require re-drilling bolt holes for the idler arm and steering gear box, maybe even cutting some threads of the tie rod ends. Possibly doable, but fabbing skills would be needed.

 

Stoffregen, I know you are aware of this, but this post is mainly for others who will not know.

 

Quote

The idler arm interference is not uncommon. Though I have never tried it, I wonder if the outboard mounted 720 idler would work.

 

Don

Edited by 620slodat
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1 hour ago, 620slodat said:

First, I have a 1973 620, made in June or July of that year (not taking the time to go out and check).My Dad bought it brand new,so I know the history.

 

It's been a couple years since I compared the 620 and 720 idler arms. Using my memory (not always accurate), the idler arms for the 620 and 720 have different bolt patterns. So if substituting the 720 arm for the 620 arm, at minimum, re-drilling one, or more, holes would be needed. Also, the 720 arm is on the outside of the frame where the 620 arm is on the inside, which might cause problems with the steering. Before I got a 720 frame I was looking at swapping the 620 tie rod with a 720 tie rod. At minimum the swap would require re-drilling bolt holes for the idler arm and steering gear box, maybe even cutting some threads of the tie rod ends. Possibly doable, but fabbing skills would be needed.

 

Stoffregen, I know you are aware of this, but this post is mainly for others who will not know.

 

 

Don

I was aware the 720 idler mounted on the outside of the frame, but I have never tried it as a direct swap. I did use a 720 front frame clip on my 320. That's how I became aware of the different steering setup. FYI- the 720 steering box also mounts outside the frame and is not connected via tube to the steering box, allowing more room on that side too.

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18 hours ago, Tony620 said:

Here's something: Looks like the PO followed this tech article to use an aftermarket Relay for the Head Lamp circuit.  It recommends using R for both the Power (30) and Signal (85) source.  

1200 Tech Wiki 620 Headlight Wiring

Anybody else try this?  It's breaking my brain.  Using R as both the Power and the Relay Signal, I'm not understanding how the Low Beam (RB)  Circuit ever gets powered.  It looks like only the High Beam (RW) Circuit is ever powered, then modulated between high or lower power states via the Dimmer switch.  If that's so: 1) how does RB ever get powered? and 2) how does RW perform in the low power state of the Dimmer switch?

RelayHeadlamp_1.jpg

 

Screenshot-20200814-131805-Chrome.jpg

 

You need to see how the red and white attached to the #86 pin is acting...

My thought is its recieving a ground signal from the cab when the lights are activated. That would send ground to the relay pin #86 sending power from 30 to 87...

Power to low beam...

If the switch is activated for high beams the ground would be removed defaulting the relay back to connecting 30 to 87a, which would power the high beams.... 

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Thanks Crash.  I think you really set me on the right path here.

 

 I think I finally got my mind right...  and I can't fault the PO since my photos weren't really good enough to act as a reference here.  Using my Service Manual circuit diagram, Crash's tip, and going back to the drawing board, NOW I think I see what the Tech Wiki was getting at.

 

1) Fused Power from Headlamp Switch (R)=30

2) Relay Coil Power also from Headlamp Switch (R)=85

3) Relay Coil Ground via Dimmer (RY)=86

4) Low Beam Circuit (RB)=87a

5) High Beam Circuit (RW)=87

 

This way, when the Headlamp Switch is OFF, no power is on R and nothing is powered. 

When the Headlamp Switch is ON but Dimmer Switch is OFF, R is powered but since the Relay Coil isn't grounded it remains Deactivated, routing R to 87a, the Low Beam Circuit (RB). 

When Headlamp Switch is ON and Dimmer Switch is ON too, R is powered AND the Relay Coil is now grounded through RY and Activated, Opening the 87a circuit and Closing the 87 circuit, routing R to 87, the High Beam Circuit (RW).

 

I'm posting this here 1) for folks to shoot it down if I'm dead wrong, and 2) in case my phrasing (if I'm right) helps anybody to better grasp this concept.

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24 minutes ago, banzai510(hainz) said:

I'll do that then!  Best to keep with convention in case I ever become the PO the NO (next owner) will be less likely to cuss me out..  Swapped Coil Power and Ground leads below to reflect Hainz's recommendation:

 

1) Fused Power from Headlamp Switch (R)=30

2) Relay Coil Ground via Dimmer (RY)=85

3) Relay Coil Power also from Headlamp Switch (R)=86

4) Low Beam Circuit (RB)=87a

5) High Beam Circuit (RW)=87

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85

23 minutes ago, banzai510(hainz) said:

I have never known a relay to care if 86 or 85 is power or ground... just needs both to trigger .... 

The other 3.... 30, 87, 87a should be the larger wires going to and from the load and source.... 

 

I would definitely make sure the wiring is the correct gauge from the source to the load....

 

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2 minutes ago, Tony620 said:

I'll do that then!  Best to keep with convention in case I ever become the PO the NO (next owner) will be less likely to cuss me out..  Swapped Coil Power and Ground leads below to reflect Hainz's recommendation:

 

1) Fused Power from Headlamp Switch (R)=30

2) Relay Coil Ground via Dimmer (RY)=85

3) Relay Coil Power also from Headlamp Switch (R)=86

4) Low Beam Circuit (RB)=87a

5) High Beam Circuit (RW)=87

Looks good to me.....

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2 hours ago, Stoffregen Motorsports said:

I was aware the 720 idler mounted on the outside of the frame, but I have never tried it as a direct swap. I did use a 720 front frame clip on my 320. That's how I became aware of the different steering setup. FYI- the 720 steering box also mounts outside the frame and is not connected via tube to the steering box, allowing more room on that side too.

 

This post will be a bit off topic, as my last one was.  Stoffregon, I was aware that the 720 steering gear box was on the outside of the frame. The 620 and 720 frames are identical, except for the steering. I even have a 620 King Cab setting on the 720 frame, and it fits without any changes. And, according to my measurements, the 620 standard cab will also fit.

 

Don

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16 hours ago, 620slodat said:

 

This post will be a bit off topic, as my last one was.  Stoffregon, I was aware that the 720 steering gear box was on the outside of the frame. The 620 and 720 frames are identical, except for the steering. I even have a 620 King Cab setting on the 720 frame, and it fits without any changes. And, according to my measurements, the 620 standard cab will also fit.

 

Don

What I'm not sure of is the tie rod length from joint to joint. It is likely that the 620 has a different C to C length, but maybe not. If someone had those measurements for comparinson, we could put this theory to bed.

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8 hours ago, banzai510(hainz) said:

Crash

yes you can swap them on the trigger 85 and 86 but some have that diode in there to prevent back feed. so I shown conventional(standard hook up hook up

Your right ... it would matter with the ones with a diode.... 

I forgot about those ... I usually just add the diode myself so it has never mattered to me...

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Stoffregen, I don't have that measurement, but I wish I did. That measurement is likely to change slightly as the width changed between the wheels over the years of the 620 production. I'm just guessing at this point as I don't have that measurement. I don't have the time right now, but I might be able to put together the 1973 620 tie rod and get the measurement.

 

Don

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