Right Side Brake Light Doesn't Work

[kings1527]

I'm having trouble getting my right side brake light to work. Here's what I know:

1) I've tested the bulbs and it's not a bulb issue.

2) I've tested the boards and all connections are fine. I have continuity in all spots.

3) I checked the brake switch at the brake pedal (with the green/purple wires coming from it) with a multimeter and I show 0.0 ohms when the switch is activated. That leads me to believe the switch itself is fine.

3) My turn signal, running light, and reverse light all work fine on my right side. It's only my brake lights (both of them on the right side). Everything works on my left side.

I find it hard that somewhere down the line I developed a wire problem. Does anyone have any ideas on where I should look? Thanks!

[WelmoedJ]

I'm having trouble getting my right side brake light to work. Here's what I know:

1) I've tested the bulbs and it's not a bulb issue.

2) I've tested the boards and all connections are fine. I have continuity in all spots.

3) I checked the brake switch at the brake pedal (with the green/purple wires coming from it) with a multimeter and I show 0.0 ohms when the switch is activated. That leads me to believe the switch itself is fine.

3) My turn signal, running light, and reverse light all work fine on my right side. It's only my brake lights (both of them on the right side). Everything works on my left side.

I find it hard that somewhere down the line I developed a wire problem. Does anyone have any ideas on where I should look? Thanks!

I miss you reporting having checked Voltage on the card edge wire connector for the brake lights (Green/Purple wire).
Both left and right units share power, so it must be something "upstream" from the unit.
Check no 41 connection on the black bulkhead connector for continuity.

[DMC5180]

I miss you reporting having checked Voltage on the card edge wire connector for the brake lights (Green/Purple wire).
Both left and right units share power, so it must be something "upstream" from the unit.
Check no 41 connection on the black bulkhead connector for continuity.

The GP wire in the black bulkhead connector feeds both brake light assemblies. The left side works so the Bulkhead connection is good. I'd recheck the terminal in the right side circuit board connector for cleanliness and that it's making a positive connection to the board traces. If you have original boards make the sockets are secured firmly to the boards.

Do a continuity test between the Black bulkhead connector and the right side board connector.

[OverlandMan]

FWIW - 95% of issues like this that I've run across after testing the bulb, switch, board, etc. are ground-related. I had one guy who's ground was connected and you could read continuity but the ground was weak and yielding erratic behavior.

[Dangermouse]

If you have a willing assistant to press the brake pedal, you should be able to measure whether you have 12V in the socket, which more than likely you do. Then it is a ground issue, as mentioned above.

EDIT -as this is a restoration, have these lights ever worked in your ownership, or is this a new problem?

[Jonathan]

Another idea to rule out bulbs or boards would be to take the right side one all as is (i.e. bulbs in place) and swap it over to the left side. Do the same for the left going to the right location. Figure out if your problem moves from right to left or stays where it is.

+1 on the grounds suggestion from what I've read here so far.

[Silverbullet]

I had the issue... turns out the socket where it was rivited to the board was loose. I bought really small machine screws with nuts, and put through the rivit, tightened them up, and now it works great... Also I lightly used a wire brush, where the Plug connects to the board...

Try having someone hold the brake pedal down (Key On, they don't work when off) and move the plug and light sockets around....

Craig

[WelmoedJ]

The thread starter still hasn't confirmed there is 12V power on the connector of the non-functional brake lights.
Having power on the other unit doesn't mean there has to be power on the other unit.
A wire could have been broken.

I did not check if the bulkhead connector runs one wire towards the brake lights, or it has two wires in the loom.
Considering one wire, there ought to be a spit somewhere.
Also considering all contacts in the bulb sockets are reported to have been good, the wire to feed the defective lights can be the only cause of the problem.
So check for 12V at the brake contacts of the card edge plug (not the circuit board).

[DMC5180]

The thread starter still hasn't confirmed there is 12V power on the connector of the non-functional brake lights.
Having power on the other unit doesn't mean there has to be power on the other unit.
A wire could have been broken.

I did not check if the bulkhead connector runs one wire towards the brake lights, or it has two wires in the loom.
Considering one wire, there ought to be a spit somewhere.
Also considering all contacts in the bulb sockets are reported to have been good, the wire to feed the defective lights can be the only cause of the problem.
So check for 12V at the brake contacts of the card edge plug (not the circuit board).


Just checked. It's a 2 wire (doubled) output from the black bulkhead connection. So, yes a broken wire from that point is possible.

[OverlandMan]

Try having someone hold the brake pedal down (Key On, they don't work when off) and move the plug and light sockets around....

Craig

I'm 99% sure my brake lights aren't a keyed circuit, in other words they work with the key off or removed altogether. I'm at the office right now otherwise I'd go test to make sure that's correct. Maybe some others can chime in.

BTW - the ground issue I mentioned earlier traced back to the connection between the connector plug and the board. Those plug connector pins are sprung and only make contact on one side of the board if I remember correctly. When you plug and unplug a few times those sprung pins tend to lose their spring and thus bad connections sometime result. Could be ground or any of the (+) connectors as well.

Invest in a power probe if you're planning on doing much electrical work yourself. They'll save you a bunch of trouble in diagnosing problems.

[kings1527]

If you have a willing assistant to press the brake pedal, you should be able to measure whether you have 12V in the socket, which more than likely you do. Then it is a ground issue, as mentioned above.

EDIT -as this is a restoration, have these lights ever worked in your ownership, or is this a new problem?

Hi everyone. Thanks a lot for the responses. Sorry...today has been an incredibly busy day. I've had the car for about seven months and its always had this problem. I just got the car running again about a month ago, so I've just been able to tackle this.


I'm 99% sure my brake lights aren't a keyed circuit, in other words they work with the key off or removed altogether. I'm at the office right now otherwise I'd go test to make sure that's correct. Maybe some others can chime in.

BTW - the ground issue I mentioned earlier traced back to the connection between the connector plug and the board. Those plug connector pins are sprung and only make contact on one side of the board if I remember correctly. When you plug and unplug a few times those sprung pins tend to lose their spring and thus bad connections sometime result. Could be ground or any of the (+) connectors as well.

Invest in a power probe if you're planning on doing much electrical work yourself. They'll save you a bunch of trouble in diagnosing problems.


Just checked. It's a 2 wire (doubled) output from the black bulkhead connection. So, yes a broken wire from that point is possible.

Thanks for the info on this. I haven't had a chance yet to check for 12v power but I have a power probe and I'll check it out and report my findings.

I checked continuity in the board but I have no idea why I didn't think of swapping boards. Great info on the pins on the connector. I'll swap boards around and see what I see. If not, I'll start assessing the double wires and the bulkhead connector.

Thanks again guys! I appreciate it! Let me know if any other ideas come up.

[Jonathan]

Hey Alex,

Don't underestimate how helpful that "tiny nuts and bolts" solution can be for fixing problems on the original taillight boards. I bought a couple little bags of the nuts and bolts from Radio Shack, put them through the rivets on each bulb socket, and have never had another problem.

http://www.dmcnews.com/Techsection/tailights.htm

[kings1527]

Hey Alex,

Don't underestimate how helpful that "tiny nuts and bolts" solution can be for fixing problems on the original taillight boards. I bought a couple little bags of the nuts and bolts from Radio Shack, put them through the rivets on each bulb socket, and have never had another problem.

http://www.dmcnews.com/Techsection/tailights.htm

:thumbup: Thanks Jonathan! I appreciate the link and I'm going to pick up the part numbers you mentioned. I'll install them as I'm figuring out this little situation. Sharing those part numbers makes life incredibly easy for other owners. Thanks again!

[kings1527]

Apparently, the solder connection on the tab of the board had worn off and was causing a bad connection. It was weird; continuity everywhere but ultimately just a bad connection. Moving the board to the other side didn't change anything. The actual pins on the connector looked ok; they weren't bent back or anything. But they wore away the connecting solder on the tab which caused a bad connection 95% of the time (unless I finessed the connection into a certain position, but there's no way it'd stay like that under driving conditions). I went ahead with Jonathon's recommendation and put the machine screws and nuts on all the holders. I'm also going to put a couple small dabs of solder in the connection area on the tab for the brake lights to improve the connection between the board and the pins. Thanks again for all the help, everyone!

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