Rear Turn Signals and Reverse Lights

[mattyd7]

I just bought a 1979 Spider and want to get it on the road ASAP to enjoy the rest of the summer. Unfortunately, I have one issue to solve before I can pass inspection. Wanted to throw it out to you guys in case there is something Spider specific that this is indicative of, before I go and pin-out all the wires to figure out where the fault is.

The rear turn signals and reverse lights do not light up. Either side. The brake lights do work. Also, the front turn signals both work, so the signal is going out, just not making it to the bulbs. The previous owner passed his last inspection, so all of these went out recently, and either at the same time or about the same time. Since this means 3 separate signals stopped working (left turn, right turn, reverse), I find it very weird. If the brake lights also did not work, I would assume a ground fault, but they all share a common ground (black wire in rear), so I'm not convinced that is the right place to look first.

Also, it seems like it would be unlikely for the circuit card to fry all three of those paths at once, right? I would expect all paths or just one.

Thoughts before I dive in with my multimeter?

[azruss]

the reverse light is actuated with a switch on the back of the tranny. I think this grounds the circuit.
The light circuit cards can look okay and be a problem. The connections between the bulb sockets and the card are mechanical. First, check the bulbs and give the bulb sockets a good clean. check the sockets with a meter using a chassis ground, not the card ground. There are old age issues with the card and sockets. They are a mechanical connection that goes south with age. You can use a jumper wire to bypass each connection to see if you get light. I had to solder 3/4 of my board connections, both on the power side and the ground side.

[bradartigue]

The setup of those rear lamp assemblies and boards is both simple and stupid, combined with a poorly made circuit board. For starters you have a single, weak ground at connector C43 (on the wiring diagram), which is the left side circuit board connector. Find that ground and test it, clean it, replace it, augment it, whatever. It has a lead to the body then another lead, via connector C42, to the right side tail lamp. The right lamp is not otherwise grounded. You can splice that line and ground it before it goes into C42, which really helps with things. So while you are right saying it has one ground, etc., it has one ground that is jumpered over to the other side, and you have to test the whole thing.

Test the ground and the leads in. If the +12V leads are dead then you need to:

- Test at the hazard switch. It controls all kinds of stuff and can partially or completely fail. Easiest way to test it, turn it on. If it works then move along.

- Test the flasher itself. FIATs flashers have their own pole sequence so an off the shelf flasher usually won't work. Electronic flashers cause all kinds of problems b/c they never get enough power.

- Test that you have the right bulbs in every position, even the fronts. I once had dual filaments in the fronts that the car didn't like and it was maddening to diagnose until I pulled them. Any burnt or missing bulb seems to make things miserable.

If you know anything about electronics and how power flows these cars may drive you insane. The grounding and high resistance of the body metal seems to cause phantoms, turn on a front light and a rear light turns on because the side marker bulb is out. Weird stuff...

[mattyd7]

I just wanted to give an update on this for anyone it might help. After the replies I got indicated that I just needed to get in there and start working on it, I took bradartigue's advice and bought a full set of bulbs for the car. When I took out the circuit cards for the rear lights, I could see that there was a lot of built up corrosion everywhere. I cleaned all the contacts for the connectors and then removed all the bulbs, which were covered in corrosion. Used a dremel with a mild abrasive tip on low speed to shine up all the bulb sockets. Checked continuity from the edge connectors to each sockets to be sure there weren't any shorts or opens. Installed all the bulbs with dielectric grease. Hooked it all back and now all my lights work! Thanks guys, I guess I should've just started there, it was a lot simpler problem than I was assuming. I guess it was just weird luck that the same lights were out on both sides.

[bradartigue]

That is fantastic, and a good lesson to the late Spider owners: that "circuit board" needs a good cleaning now and then.