1967 Electra - No Tail lights

[dmfconsult]

Need some help tracking this problem down.  When bringing the car out of winter storage this year, I noticed that my tail lights were non operational.  I have signal lights and brake lights, but no tail lights or licence plate light.  Simple problem I thought to myself, just the fuse, it looked fine but replaced it anyway... no joy.  Next step was the headlight switch.  Found a spare (untested) switch I had in my parts bin that I took from a parted out LeSabre and put it in thinking again this would solve my problem, but no.  This is a very simple circuit, so what am I missing?

 

I seem to only have time to drive the car at dusk or night these days, which is a problem with no tail lights.  I find it hard to believe that both head light switches I have have failed in the same way, but I guess it's possible.  Before I order a new head light switch, I thought I'd seek ideas here first. The wiring I traced before it goes into a loom looks fine, so I don't think that's an issue.  

 

Thoughts?

Edited August 13, 2023 by dmfconsult (see edit history)

[JohnD1956]

Any cuts in the wire in the trunk or top cylinder area.

 

[dmfconsult]

The wire goes into a loom with all the rear end wiring into the quarter panel and then under the carpet.  I've chased it back a little, but haven't pulled the back seat to check the wiring throughout.  I presumed (maybe wrongly) that given it's wrapped with many other wires, that it's unlikely been cut.  I did check what I could see, and all looks fine.  I'll admit to trying to avoid a full interior dismantle to track the problem, so I'd likely order a new head light switch first as it's only about $40 and pretty easy to swap out.   The switch I put in there was not tested, so I don't know if it was "good" before...

[JohnD1956]

Did you check for voltage at the rear lights (just in case there is a huge coincidence with all those light bulbs back there? You could also test your original light switch now that it is out of the dash. I am no electrician but I believe you can hook up a small 9 volt battery to its power terminal and then just use a volt meter to see if the other terminals have power as needed. 

 

[EmTee]

Do you have a schematic?  I would try unplugging the headlight switch and applying 12V to the tail light wire (brown wire?) directly, bypassing the switch.  If the lights work, then check the 12V input at the switch.  If that is good, then replace the switch, otherwise trace the missing 12V feed, or the wiring out to the tail lights.

 

Edited August 13, 2023 by EmTee (see edit history)

[dmfconsult]

Ok thanks for these. Both good ideas. I did check bulbs first and was getting no voltage at the 3rd taillight only bulb.  Soon after that my multimeter crapped out too. 
 

I like the idea of running 12v directly to the correct wires to the tail lights. I’ll pull the plug and try that. I do have the schematic from the chassis service manual and there isn’t much to that circuit.  Might have to go for a drive tomorrow first though. 
 

I’ll also give the 9v battery a try, at least once I repair/replace my multimeter.

Edited August 13, 2023 by dmfconsult (see edit history)

[bhambulldog]

The grounding may be bad or weak. 

[dmfconsult]

Ground was my first thought but strangely the chassis service manual shows a ground for LeSabre and Wildcat but not for Electra. It may be ground at or near the Licence plate lamp but I couldn’t find one.  

[Bloo]

Well it has to have one whether it has one or not. In the 60s it was still pretty common to just rely on whatever metal was nearby to be a good ground. It often wasn't good, and today it almost never is. If there is a question, test by attaching a wire to some solid ground like the negative battery post or the block or something and touching the other end to the shell of the bulb socket.

 

Are you sure there is not a connector somewhere in that wire harness that runs from the front to the back of the car? I don't know if Buick did that on the 67 Electra, but it was common practice in the 60s, and it would kind of surprise me if they didn't. If the connector is there and has been wet, you might find it's blades reduced to a bunch of blue powder.

 

[Frank DuVal]

4 hours ago, dmfconsult said:

but no tail lights or licence plate light.  Simple problem I thought to myself, just the fuse, it looked fine but replaced it anyway... no joy.  Next step was the headlight switch. 

If the front parking lights were working then the light switch is OK. In 1967 the front parking lights come on with the headlamps, so they share the rear running lamp circuit. Not that I can confirm this on the Team Buick provided shop manual online. I can confirm that the front cornering lamps are powered from the Brown taillight wire off the headlamp switch. So if they work, then the headlamp switch is good.

[EmTee]

6 hours ago, Frank DuVal said:

In 1967 the front parking lights come on with the headlamps

I don't think so - that's not the case on my '67 Riviera.  I think that started for Buick (and GM in general) in 1968.  If the brake lights work It seems the ground is OK.  I think there may be a connector for the rear harness somewhere under the car.  Look along the left side between the gas tank and quarter panel.

[M1842]

Spent many hours working on my 55 to find wiring and ground faults with a multimeter.  Makes trouble shooting more scientific.  Check power and ground at the socket.  Check continuity of the power wire.

 

I always start simple, is there a problem with the bulb itself?

Edited August 13, 2023 by M1842 (see edit history)

[dmfconsult]

@Frank DuVal for 67 the parking lights come on initially with the taillights on the first position of the switch, but go off when the headlights are activated while the taillights stay on. The taillights are also on their own fuse. I think EmTee is right that it was 68 where they stayed on. 
 

The wiring harness runs along the floor under the carpet so a few things have to come out to check the length of it.  That car hasn’t seen rain in years so I’m sure there is no water sitting in the floor, the only fluid would be from the top cylinder. The bulbs are fine and four of the six bulbs for the taillights activate for the brake lights and signals.

 

I will test the switches I have once I replace the multimeter as that is the most likely issue, just random both switches failed in the same way. I like to start with the simple things first so that will be next!

 

 

 

[Barney Eaton]

Seems like GM wiring during your time period wired the instrument cluster lighting with the taillights..... it was always a clue if the IP lights were out,  the taillights were also. 

usually a fuse,  are you sure you replaced the correct fuse.......... just trying to help. 

[dmfconsult]

Thanks Barney, and yes I changed the correct fuse, twice in fact just to be sure!  The instrument panel is also on a separate circuit for 67 and they do still work. The taillights and Licence plate light are the only things on a 20A fuse. 

[EmTee]

Is there power at the fuse?  If so, you should have power at the headlight switch - check that to confirm.

[dmfconsult]

I just picked up a new multimeter (couldn’t fix the old one) so will check. I also pulled back some of the wire wrapping in the trunk and found a previous repair to the brown wire so will check that as well. Luckily my son is around tonight so I’ll get him to assist!

[EmTee]

A test light is handy for troubleshooting issues like this.

 

 

8 minutes ago, dmfconsult said:

I also pulled back some of the wire wrapping in the trunk and found a previous repair to the brown wire so will check that as well.

That's a good find!  I'm 95% certain the taillight wire is brown...

[dmfconsult]

You are correct the tail light wire is brown. 

OK here’s the report. Thanks to @JohnD1956 for the 9v battery trick, it ended up saving quite a bit of time and crawling around. As I had the switch and connector, I could simply go through all the wires and test in the comfort of A/C in the house. The trick is that the headlight switch gets power from two sources I believe, battery (red wire) and tail light fuse (brown wire with white stripe).  The schematic shows the brown WS wire coming from fuse to switch and feeding the brown tail light wire.  I’m not sure why it would have two power sources but that’s the way it appears based on the schematic. 
 

 

The bottom line is that the switch works as it should. I also tested the tail light fuse and I have 12v at either side with the lights on.  The repaired wire at the back appears to have only the insulation cut but there is no power to the exposed wire there, so I don’t think that is the issue (although I may look at that again and triple check)

I’ll pull the connector from the switch in the car next and see if I have power to the brown with white stripe wire, if not there is likely a cut in that wire between the fuse and the switch. Looking forward to contorting myself to trace the wire under the dash!  
 

Thanks for everyone’s help so far!

Edited August 14, 2023 by dmfconsult (see edit history)

[dmfconsult]

Here’s the exposed wire in the trunk. 

[Frank DuVal]

Do you have cornering lights? If they work the headlamp switch is good. The feed for the cornering lamps comes after the headlamp switch (as cornering lamps only work when the taillamps are on) on the wire to the rear lamps.

 

Unfused power feeds the headlamp switch for the headlamps, as there is an internal circuit breaker for the headlamps. The rear taillamps get power through the Taillamp Fuse, that feeds the headlamp switch. There may be more sources of power to that switch too, like instrument lamps, but that is not part of the current (pun...) troubleshooting.

 

Since the exposed wire in the trunk already has damage, stick a pin (yes, a seamstress pin) in the brown wire with the headlamp switch on and see if there is power in the wire. On a good insulated wire a small smear of RTV will seal the insulation after the pin is removed. This is a common troubleshooting technique.

[dmfconsult]

I do have cornering lights but at some point in the cars history the signal light switch was replaced with a non cornering light switch. I have another but haven’t gotten to removing the steering wheel to replace it. 
 

I think the cornering lights work when the headlights are on and are independent of the tail lights, but that’s not something for another day. 
 

Good tip with the pin, I’ll do that a few inches behind the cut (switch side) and see if I have power. I guess all I’ve proved so far is the switch I took out was OK so hopefully the one I put in is OK too (the movement is more finite and less sloppy than the one I took out).

[EmTee]

6 hours ago, dmfconsult said:

Here’s the exposed wire in the trunk. 

That tells me a previous owner has likely troubleshot the same issue on this car before.  Since the fuse has power and you have the schematic, you can check for power at the brown/white wire at the headlight switch.  Since this is a convertible, I can't help but think there may be an issue with the harness where it passes through the top well.

[dmfconsult]

Perhaps, but I’ve owned this car for 21 years and this problem is kind of out of the blue. There have been several electrical gremlins lately though, so I’ll just continue to chase them down.