GRipp 73

Ok, so I have been trouble shooting this all day and am finally turning to the web for help.

No matter what I do, I can only get the drivers side brake light to activate when the brake is pressed. Here is what I have done thus far.

Checked the fuse.
Replaced the brake switch (when I went to look at the switch, it fell apart into two pieces exposing the spring, so got a new one). I have even flipped the brake switch on the contacts.
Replaced the bulb
Switched the bulb with the known good side, placed the supposed bad bulb and placed it on the good side and it works. So bulbs are both good (even bought two new ones just in case)
Then I thought it was the pig tail at the brake light as I wasn't seeing a consistent voltage when metering it.

Now for the really confusing part, I can meter both the known good side brake light and compare it to the "bad" side, they both match up. Brake pressed, I get 12V on the non-brown wire (yellow on drivers side, green on passenger side) between ground and the positive connector off the pig tail. I have moved the ground around, and even ran a direct wire from the ground bolt on the frame directly to the grounding bolt on the tail light housing. I can do a continuity test between the ground bolt on the tail light housing and the inside of the bulb housing and i hear my beep. I can also test between the ground bolt on the tail light housing and the brown wire on the pig tail and I have continuity there too.

So what am I missing? Both my rear parking lamps are working just fine, and I press the brake and the drivers side lights up nice and bright, but the passenger side just stays dim with the parking light on.

There has to be something I am overlooking or making more complicated than needs to be, but I am stumped.

thegazman

I had a similar problem with my 79. Found problem by accident. The ground wire was lose inside the bulb socket.

GRipp 73

That's kinda the last thing I think it could be is the tail light housing unit itself with the bulb socket that seems to be built into the unit. There is a wire that goes from the ground bolt on the housing unit to the bulb socket? If there is, it must be internal to the whole housing unit. Thanks Gazman.

I am getting ready to switch the two tail light housing units to see if the problem follows. Wish me luck.

PeteZO6

GR I'm impressed with your trouble shooting! So often people call for help here on the forum without testing everything first. Not only did you do that, you wrote it up clearly with plenty of detail.
I'm thinking it has to be that socket. Let us know.

Pete

mds3013

Can you test the socket with the brake light circuit energized and the bulb in place? The reason I ask this is, it takes very little current to show 12v on a meter but takes a lot more "current" to light a bulb. If you are showing 12v on the offending socket but the bulb will not light, then I am thinking that you will see the 12v disappear when you energize the bulb due to inadequate current flow. On stranded wires it only takes one strand to show 12v on a meter but it takes most of the strands to light the bulb. Current flow seems to be the problem. I hope this makes sense. mike...

GRipp 73

Well, changing the tail light housing from side to side did not change which side the bulb stays out on. It is still on the passenger side, even though that has the "good housing and bulb" now. Still have the parking light, but not the brake light.

Mike.... I think I might be able to. Actually, I know I can. Wires don't scare me and I like the electronics (as long as things are labeled). But what I don't want to think about is pulling the entire wiring harness just for this one issue.

I am going to take a break, eat some dinner with the wife and then try again after dinner. Thanks for the idea on current flow, I think you are on to something. But then how do I trace down where the current dies and how to get a good wire back into place?

mds3013

Test voltage with bulb/load in place first. If voltage does indeed drop to below 12v then you will know it is a bad connection/partially broken wire. Only way to find it is to backtrack to voltage source. Good luck with it. mike...

'75

Does the signal work on the left rear?

GRipp 73

You were right Mike, the voltage drops with the bulb in place. Time to trace the wire. It is all wrapped up in its harness, so I hope it is just the other end that might need tightening?

You know '75, I could have sworn the directional worked on that side, but it doesn't seem to now. So the bright filament for the brake and the turn is not working currently on the passenger side. And the hazards flash very quickly, except the this tail light as it does nothing :-)

Time for a beer yet?

'75

Go to the harmonica connector at the steering column and check the yellow wire for power with the left signal or the brake on. Check it with a test light if you have one. No power there indicates the signal switch is at fault, Power there indicates the wire is faulty between there and the left rear.

mds3013

You have my permission to have a beer. '75 is a good guy to listen to. Good luck and press on. mike...

mds3013

One final thought. To determine if you are losing the 12v pos. or 12v ground. Put one meter lead to a known good ground and other meter lead to the 12v pos. supply to the bulb. If you do not have 12v pos. when under load then the feed wire is the problem. If 12v remains when under load with one meter lead to known good ground then you are losing the ground to the socket. Long test wires with alligator clips on the end come in very handy when doing this type of work. mike...

GRipp 73

Thanks you two. Wish I had asked earlier in the day. The fault is in the steering column, or, at least in the right turn signal switch somewhere. I randomly tried the switch again giving it a few "good" jerks (while talking to the father-in-law on the phone) and the rear turn signal started flashing brightly.

I did not try finding that yellow wire yet '75, as it is too late, and too dark in my garage. Got a couple of shop lights but they are over the engine bay and not under the rear where I had been all day.

So for the moment, I have the entire rear end lighting system working.

Biggest find of the day was the beautiful spare tire inside the carrier. Well, the rim is great, the tire is very old, but it was holding air and surprised me.

Thanks for the help, I'll be looking into the turn signal switch in the near future.