Left rear lights out even with new wires

[Geoman]

Well now that I've accomplished what I wanted to get done with the engine and brakes, I'm onto the electrical. So while the engine is running I checked the function of the exterior lights. It appears that all are working except the left rear trio, at least the left two (haven't checked the reverse light). Here's what I've done:

1. removed entire assembly
2. found a good size nick in the common black ground wire that connects all three lights
3. completely replaced this wire: new connectors, new wire
4. removed the corrosion on all male tabs on the light assembly
5. removed corrosion on/in the light sockets
6. installed new bulbs
7. reassembled unit

Still no luck.

The other side works fine. I noticed that the right front turn signal only blinks when the headlights are off. When you turn the headlights on, the turn signal stops flashing. Also the right signal blinks at a slower rate than the left one.

Any suggestions as to where to begin? Thanks!



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[Farace]

My problems with the rear lights (well, the front and sides, too) have all been caused by poor grounds. The "run a screw through some ring terminals into the sheet metal" method of grounding seems unreliable. What I've done is to make sure the ring terminals are clean, the screws themselves are clean, and I've scraped paint away around the screw holes where the ring terminals contact the body.

Mind, you should invest a few bucks in a simple test light. Clip the alligator clip to a known good ground and probe with the other end and follow the power into the lamp unit. You'll be able to confirm that you're getting power into the sockets. But I'm betting on the ground connection to the body. If you have an ohmmeter, you can test for continuity between the grounds on the lamp unit and the body.

[Geoman]

Thanks Bob for the tip! I'll check the grounds tomorrow.

[Geoman]

Update: The grounds under the left front corner of the dash were very corroded, including the area of the metal to which they attach. I ground down the metal so it's clean, installed new washers, screw, and ring connectors....and the rear turn signal is back! The middle light still no go. I used a multimeter and found continuity between the common ground of those rear lights and the ground to the other set of lights. Perhaps the socket needs to be checked. Now I'm cleaning up the two sets of ground just in front of the radiator for the two front lights, we'll see what happens.

[Geoman]

Ahh ha! When I removed the other set of rear brake lights I found electrical tape wrapped around the wire supplying power to the right turn signal. Thinking that's odd, I unwrapped it and found that the wire was crimped and the copper was exposed. Nothing like a PO to "fix" an electrical problem for you!! After replacing the wire, the blinking rate was back to normal (was very slow before) and for an added bonus, the left high beam was back! Gee, what else will I find....