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79' 620 electrical gremlin help


Hooligan

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Ok.... just picked up a 1979 620 a couple of days ago. Previous owner said they had lost brake lights one day.... a couple of days later they worked again. I drove it home from Oregon with both brake lights working and both turn signals working. 

 

Yesterday I had it on the rack at work and and we noticed the passenger brake light is working, but not the drivers side.

 

Today.... I have running lights, no brake lights, passenger turn signal works, drivers signal does not work.

 

Now.... When you turn on the right turn signal you can hear the flasher click under the dash, no light on the dash, but the turn signal works. When you turn on the left signal you dont hear the flasher, no light on the dash, and no signals work.

 

As for the brakes... if you check power at the brake light switch, the brake light switch is working correctly. 

 

I know this is alot... just driving me nuts

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Look for the frame harness where it plugs into the tail light harness behind the passenger side tail light. It's a round plug. I find this gets lots of rocks and water spray. Unplug and plug back in several times and make sure that the pins haven't been jammed and pushed out. See it that gets them going.

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Under the pass seat is a 10 pin connector. Retract the seat to get at. This is the cab to frame harness. If everything is good there then the frame harness may be damaged and those wires (copper) will corode to blue powder. I had tail light problems with my 521. Turned out some dick spliced in a trailer plug then cut it off and wrapped it with tape. Water and salt gets in and....

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If you havnt found it yet... and if your fuse block looks like this, replace it...

2012-06-14_18-25-13_299.jpg

 

this was to get my running lights working when I first got my 521.  It also had a corroded wire from fuse block to the connector under the dash.

 

The blue wire is the new replaced one...

2012-06-14_18-22-12_445.jpg

2012-06-14_18-22-52_763.jpg

 

 

Ohm the wire harness in sections to help eliminate the good areas...

 

I also had my brake lights not work...in a 521.  

 

First checked the brake switch under the dash... jam screw driver in derr...

2012-08-20_17-20-33_424_zps82d652f5.jpg

 

its good...next... I just jumper hard wire to brake light.. 

2012-08-20_17-33-49_718_zps8c08f173.jpg

 

2012-08-20_17-32-54_625_zps6fe16946.jpg

 

tested the harness from firewall back... good...next...

 

so, down to under the dash to the brake switch...

2012-08-20_17-40-26_511_zps0cea37a1.jpg

 

there it is...

 

2012-08-20_17-53-32_607_zps24a7f01f.jpg

 

now for those that dont know, to get these buggers out. need to poke somethin in there and hit the little latch that holds it in place...

 

2012-08-21_16-17-45_460_zpsf7c63464.jpg

 

2012-08-21_16-18-38_613_zps7c8c9e62.jpg

 

 this thing holds it in the plug...

 

Yay, more corroded connections...

 

2012-08-21_16-41-46_944_zpsc2ffd60d.jpg

 

anyways...  When in doubt, Ohm It Out..  HaR Dee har HAR... 

 

 

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I want to thank everyone for the help. After tearing into this.... it still wasnt making any sense. In the end..... the damn main harness connector had a pin come loose and when the two would latch together it would push the loose pin back causing it to lose connection

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When I got my 79 620 most everything kinda-worked, but poorly and when it wanted. The ghost logic of when and why it worked was crazy like yours.  I had already cleaned the battery terminals at the battery as the cables looked good. Next I was working my way thru cleaning all the little individual problem component connections with little success.

 

When I was good and frustrated...I got a "real charge" to find the battery connection at the block was actually tight, but had an oil leak dirty grease build-up over a russsstty connection. The pigtail to body connection was just as crappy. After cleaning just these two points along with the starter connections the majority of of electrical stuff worked like new and the engine ran way better. The real electrical problems were much easier to problem solve after.

 

To me it isn't a process of elimination. I prefer looking at it as establishing a strong power and ground circuit base to begin with before working on the outlaying smaller amp and ohm drawing circuits.

Hope this helps?

 

(Now all I have to figure out is why they ran a piece of crappy speaker wire from the fan blower motor under the dash to the passenger side, thru the firewall and to tied it into what looks like the elec choke???   First time I found about it was when I pressed my bare leg up next to the fuse box and it branded my leg it was so hot. So I figure something something in the heating or elec carb circuit is screwy.

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