Tail (brake) Light Issue

[Gary L]

This is on my 76 2+2. The other day my daughter was following me home and when we arrived she said my right (passenger) side brake light wasn't very bright.  I don't know how long it's been like that, may be ever since I bought the car a couple of years ago and then some.

Anyway, when I put the brakes on, the parking element on the right side lights, not the brake element. When I turn the parking lights on, the correct parking element lights, but then if I also put the brakes on, neither element lights. I tried switching bulbs, but it doesn't change anything. The left side (driver side) lamps seem to work fine. 

Any ideas where in the wiring harness I should start to look. Again, I have no idea how long it's been like this, but it's almost like a prior owner got some wires crossed or something. I don't think it could have come from the factory like that 40 years ago.  I did check the connector proximal to the lamp and it seems fine. I didn't yet pull the passenger's seat out to get at that connector. But again, it seems more like wires somehow got crossed verses just a dirty connector or ground?

Thanks

Gary

 

Edited August 19, 2016 by Gary L

[Zed Head]

Have you taken a close look at the socket the bulb sits in?  I had one get so hot the electrode melted the plastic and it shifted sideways and shorted.

[Gary L]

The socket looks to be fine, same as the other side. I haven't checked things yet with my volt meter, but when someone else comes home tonight, to press on the brake pedal, I can try some testing that way. 

[Gary L]

Well, just checking the parking light pin in the sockets, I have just over 10 volts on the left side and only 5.3 volts on the problem (right) side. So I'm sure that is part of the dim issue, but doesn't explain why the brake light element doesn't light at all on that side.

[Patcon]

5 volts may not be enough to even make it glow...The 10 volts is pretty low too. What is the current battery voltage as a baseline?

[Zed Head]

Don't know if you're grounding to the ground pin or the body when you take those measurements but the ground side could feasibly be the issue.  Find that splice.  It's probably one of those scary looking crimp splices, buried in some tape somewhere.

Edit - actually, take a measurement from the power pin to ground first.  That will tell you if the ground is bad.

Edited August 19, 2016 by Zed Head

[Gary L]

My battery is only 2 years old and measures 12.03 volts. When I measured at the socket, I put the neg on the outside of the socket and then touched the parking light pin getting the 10 volts and 5.3 volts. Looking at the schematic, isn't the ground for both the rear lamps the same and so I'm not sure why one would work fine and the other not if it was a ground issue? 

[Zed Head]

There's a splice along the way.  The right side has essentially two ground points, one at the splice and one at the terminal end of the wire.

I put a picture n my other post.  Maybe you're reading your own schematic?

Edited August 19, 2016 by Zed Head

[Gary L]

Hi Zed, I guess I don't follow you on where there might be a splice. I'm just going by my service manual schematic and I'm not very good at this wiring stuff.

[Zed Head]

Are you on a phone?  I posted a picture from the Body Electrical chapter and underlined the splice.

The modern super phone is the worst efficiency improvement mechanism that has ever been foisted on modern society.

[Patcon]

Nissan would make splices in the harness for efficiency sake. Under the loom tape in the harness somewhere will be a small splice. They strip a little section off a wire and then strip the end of the other wire and attach them to each other with a small copper crimp. They can be hard to find. Sometime they corrode...another thing to check is take your meter and with a long lead or a long piece of wire tie the black meter probe to the negative battery post and post up your voltages again...

[Gary L]

So between where the harness comes through the grommet on the right inner fender wall and where it branches off for the right lamp (about 1 foot of wrapped wires), there would be a splice?