Taillight question

[njoconnor]

I've been waiting for Sgr Marelli to finally come a'calling, and today he did. In fairness, when I reconnected the battery, and flipped the light switch, I was amazed at what DID come on! Both front parking lights, 3/4 side markers (R front is way corroded, replacement in bound), both brake lights, and the R rear tail light. Turned ignition on, and got headlights (reg and bright), two speeds of fan ( ), lighter light, and the damn key in ignition buzzer. Plus the car starts and runs fine.

Issue the first: Left tail light does not light. I'm getting 11+ volts at the end of the yellow supply wire, and 7 and change off the brass bulb spring. Carefully touched the yellow positive wire to each of the other fixtures' positive terminals with the following results: Back up light, good (same in the right). Tailight, nothing. Turn Signal, nothing (also: same on the right side). These are the late 72/73+ 4 bulb light fixtures, using single pole bulbs in all positions. Last winter,, I did have turn signal response when I keyed the ignition and flipped the lever. Now, nothing (I have a new flasher for LED bulbs already). I get nothing when I trip the hazard light either. All connections have been dremel brushed to shiny, and I cleaned up the tail light grounds as well.

I figure I need a new flasher, and will see if the local auto folks have a generic, before I mess with the LED's bulbs (Note: I do NOT have the Speedo/indicator lights re-installed as yet). But does anyone have any ideas on further trouble shooting the left taillight, and/or how to repair the individual fixtures?

Thanks.

Neil

[njoconnor]

Well, an update of sorts. After reading (a lot!) of past posts about tail lights and things, I noted the recurring theme of the "reverse light switch". Hmm, sez I. Wonder if that's why my back-ups aren't working?

Crawl under the car, and at least I don't have a bolt inserted into the tranny. Switch was there, missing both electrical contact blades, and the wires were present and intact, if more than a little greasy. Checked the other trans I have, switch is there, but missing one of it's blade contacts. So, that switch went onto the list of things to order next.

Still headscratching the left tail light. My guitar bud suggests re-doing the already wire brushed grounds, and trying a jumper wire from the fixture to the good ground to test if it's bad ground on the fixture, or bad internals on the fixture. Turn signals will await the install of a new flasher can. I suspect that's the issue there.

Still interested in other observations/ideas.

Thanks

Neil

[SoFlaFiat]

I think your bud is right. Recheck the grounds! If you can jump straight from a know good B+ and ground to test the light itself! that will help determine where the issue is.
Good luck Neil! Chase those gremlins!

[Kevin1]

One more thing to check, as was pointed out to me by a friend last summer...

The bulb holders are riveted to the circuit board, and the rivet is what makes the connection to the underlying metallic strip. Clean these up, and then either: A: Make sure the rivets are making a tight connection, they can corrode and loosen over time. B: Solder the connection between bulb holder, rivet, and underlying metallic strip.

Assuming clean/good grounds this will eliminate almost all tail light issues.

[njoconnor]

Alan, Kevin: Thanks for the encouragement! In the 72's, Kevin, we don't have a circuit board; individual power (positive) leads to each bulb socket, with the negative grounds daisychained to a mounting bolt ground point (and it's wirebrushed shiny). As far as the brass rivets, all are tight and nothing is loose, so I have that going for me...

So. Following Alan's and Jim-the-guitar-bud's suggestion, I fashioned a jumper, turned the light switch to "parking" (middle) position, and using the taillight (yellow) power lead, checked each of the fixtures on the left rear assembly. Back up light: works! No power through its lead, since I already know the tranny switch is toast and disconnected. Tailight: nada. Still 11 and change on the inbound side, 7 and change through the socket, even with a good individual ground. Stoplight: Works! With both the yellow lead and it's own lead (when brake pedal pressed). Turn signal: works when using the tailight lead, but does NOT work when using the turn signal stalk (uh-oh). Note on the grounds: I tested the fixtures with the daisychained grounds , then again with the individual jumper to ground. Got the same results, above, with both methods. Right side is the same, except tail light always works when switch is on. Assumption: something is amiss, internally, in the left taillight socket. Any suggestions on getting in there?

Turn signals. Last winter, I could get them to flash and hear the clicks with ignition on. Now, silence. I replaced the flasher can (40 years old) with a new generic can from the local parts store. No change: silence. There is no power coimg off the power leads at the back of the car with the stalk in right or left position; ditto fronts. Bulbs are all incandescents, and all are "good" bulbs. Rear bulb siockets have been wire brushed clean; haven't gotten to the front sockets yet. Squrted contact cleaner on the column switch leads which are visible. No change. I hate to ask, but.....time for a new column switch? Remember: this is the steering wheel which will. not. come. off. I'm going to go back and check for power at the can ("P" terminal), but I'm fearing wheel wrestlingis in my future.

Thanks in advance.

Neil

[SoFlaFiat]

This may be off but it might be worth pulling the steering column cover and inspecting the wires there. It is possible that they have been pinched...

[njoconnor]

Cover is already off, and the wires look fine to initial inspection (also got a shot of cleaner....). Spoke with Csaba last night about something else, mentioned this, and he recommended checking power to the flasher can. He's thinking power might not even be getting to the switch, much less the lights. So....when time allows....back under the dash with good lighting and a multi-meter!!

Anyone ever disassembled an early taillight fixture and replaced the actual sockets?

Neil

[JEEPER]

If you are reading 7volts, I'd look suspect a bad ground, with the ground being read through a lamp filament. Take all the lamps out and read the voltage from the socket contact to a known food frame ground or run a wire from the -POST and use it as a ground. Has anyone done any electrical work that you know of? As someone said grounds, grounds, grounds. Current will follow the path of least resistance.

[njoconnor]

Thanks, Jeeper. Only electrical work seems to be the PO's vampire lead to his (former) radio (repaired that by removing the vampire wire and recovering the insulation splice). No changed work evident in the trunk at all.

I did a separate ground wire to the good frame ground, to no avail. I'm beginning to wonder if the connection inside the socket area between socket and ground may be weak/corroded. All the other lights in the fixture, both upstream and downstream on the common daisy chained ground, work with power applied. I'll go back and retrace my steps with the ground, because, yeah, it's the only thing making sense right now.

Neil

[SoFlaFiat]

I'm feeling for you Neil!!
Good luck !!

[NSFIAT]

I stripped so many things apart trying to chase a bad ground last year. All of my brake lights and signal lights would work if the headlights were off. With the headlights on, nothing else would light up. It took a while to find it (checking other grounds, cleaning up the bulb holders, etc), but the culprit was a very very tiny break in the circuit board itself. I soldered a wire over the break and haven't had any issues since.