Tail (brake) Light Issue

[Gary L]

Hi Patcon, when I put a jumper wire from the neg on the battery to the neg probe on the meter, I now get about 10.2 volts at the parking lights pin on both sides. So it looks like I do have a ground issue with the right side. I guess tomorrow I'll have to take the rear finisher off so I can get better access to the harness and look for those splices

[Patcon]

You also have an issue on the positive side which I was also trying to ascertain. 2 volts is a pretty good drop to the rear. One day when your bored clean all the connections between the front and the back and recheck the same way.

I am sorry I am having trouble visualizing your earlier description of where the splice might be Zed Head might be able to help. Clean all the ground points you can find. I don't know if @zKars hidden ground point plays into this too...

[Gary L]

So when I do the jumper wire thing from the neg post on the battery directly to the socket, the bulb lights and works like it should, both parking and brake. So I either need to find the bad ground for that side or somehow run a different ground to it (any suggestions). 

As I mentioned, I'm not very good with this wiring stuff so I really appreciate your help guys

As for the voltage drop, I had a similar drop to my head lights and cleaned every connection and ground I could find with no improvement. So I purchased one of those relay harnesses and now I do have nice bright headlights. I can try cleaning every connection to my rear lights, but in a 40 year old harness I'm not sure I'll see much an improvement there either. I think they will be adequately bright enough if I can get a good ground to it.

Thanks again guys

 

[Patcon]

SteveJ came to my house and helped me resolve a similar problem. He helped me clean the fuse box in vinegar and it made a huge difference. I posted about it in my thread in the 510 sub-forum. You could check the voltage on each side of the fuse, check them on them on the back side of the fuse box.

You should be able to find the factory grounds and fix them. They are adequate if they are clean.

[Zed Head]

Good that you have a solution path now.  I actually might be trusting that diagram too much, it shows a connection along the way, but who knows.  It could be two separate wires to a ground point.  Knowing a little about how cars are designed to be manufactured, the end of the wire might actually be back at the starting point.  But the big diagram shows all of the things in the back half of the car ending at the same ground point.  They're all behind the C-8 connector though, and C-8 is the one by the passenger seat, I believe.  Maybe under the passenger seat?  I'll go take a look in my 90 degree garage.  Where the car sits when it's over 90 outside.

[Zed Head]

Too cramped.  I would look in a spot that could get wet.  That would be why the corrosion started.  There's a relay under the passenger seat, bolted to the seat mount rail.  That would be a good spot for it, since Nissan thought it would be a dry spot.  But it fills with water if there's a leak..

[Zed Head]

A final thought - I might be assuming that the central ground point is like the EFI harness, which does have several grounds ganged in to one point.  But it might be that there are many grounds dispersed around the harness in the back.

Somebody just posted recently about a ground point buried back there for the fuel tank sending unit.  They shined it up and reinstalled it.  So there are probably several points.  The diagram just combines them for ease of drawing.  Good hunting.  Note that the wires will be black.

[Zed Head]

Back again.  I found one.  Browse the diagrams in Body Electrical if it's not the one.

 

Edited August 20, 2016 by Zed Head
Better picture

[sweatybetty]

you might check this. it makes for a very bad ground connection

 

[Gary L]

After further testing, the problem does seem to be in the socket itself as Sweatybetty suggests. However, the socket on my 76 2+2 looks a little different than in that post and I'm not sure how mine comes apart. I haven't yet looked to see if someone still sells new ones and how much they cost.  When I get more time later today I'll have to look it over better to see if there is a way to take it apart.

[Gary L]

I got it. Thanks everyone. Great forum. My socket did pull apart like the one in the above link by Sweatybetty. The ground wire was attached by a crimp connection which was all corroded. I opened the crimp to remove the wire, cleaned everything up, put it back together, re-crimped it, and it seems to work fine. When time permits, I'll have to check all the other connections mentioned above, which I've done throughout the front of the car.

[Patcon]

Glad you found it