Diagonal turn signals not working.

[silverlock]

Yes, an odd failure mode!

The front right (passenger) and rear left (driver’s) side turn signals suddenly stopped working on my ‘78 SC. I’ve made zero changes to any lights, relays or the dash/stalks on this car in the last 18 months.

1. Turning the hazards with the key off = no change. The front left / rear right work, but not the front right / rear left.
2. When using the indicator stalk, BOTH turn signal indicators in the odometer light up and stay lit (they do not flash).
3. Bulbs are OK — inspected and flushed the sockets with some contact cleaner for good measure.
4. Flasher relay is OK — clicks every 1s + this would be a strange failure mode given how the relay works internally.
5. Connectors in the engine bay are seated.

The car has the relay kit, and fuses all seem intact.

What am I overlooking / should I look at tomorrow?

[zuch]

Turn signal switch?

[rowingone]

try cleaning the terminals on the flasher relay behind the instruments . . and clean the fuse contacts as well.

[silverlock]

Current status:

* Key out, hazards on now seem to work for all three corners bar the rear left.
* Makes me suspect the flasher relay (since it is powered at all times)
* Ign on, Turn signal right = works, clicks at normal speed, right arrow flashes.
* Ign on, Turn signal left = rear left still dead, clicks slowly, both arrows lit & static. Usually this indicates a bad ground.
* Relay was a pain to pull out — really didn’t want to come loose. Pin C (to the tach) looks a bit black but the socket appeared OK. No obvious corrosion. Pulled it out of its grommet, flushed it with contact cleaner, and letting it evaporate on a rag.
* Ground G4 behind the fuel filter looked acceptable, but put a wrench on it to free it, soaked it with contact cleaner, and am letting it evap.
* Ground G3 near the battery box couldn’t look better + no other electrical issues with the car.

Have some errands to run today but next steps are to re-check the rear ground, put the flasher relay back in and see what works.

Next next step if no luck: new flasher relay ($15) + test ground between the left rear light housing + engine ground with the turn signal on to see if it lights up. Other lights that share that ground (parking, brake) are OK though.

[PopsRacer]

You know the ground on the flasher is ok bc otherwise the hazards would not work. If the left front works, it’s safe to say you have good power to the fuse, and the fuse is good and you have solid connection out of the fuse panel to the front. I think it’s also safe to say the flasher is fine. The other wire from the left-side signal fuse runs from the low side of the fuse into the body harness and then rearward. The next stop is Pin 2 of the connector T14 (left rear light). See if you have continuity from the fuse panel to the rear lamp connector, and then to the actual socket - or start with the socket.. whatever is simplest for you. You can run an aligator clip to a section of wire to get a continuity test from end to end on the car. The chances of the body harness just “going bad” are pretty slim ime. Remove the signal bulb so you don’t get odd readings as you go. Most likely culprit IME is the socket due to exposure to the elements, but if the car ever had bodywork it is also always possible someone cut the lighting harness to remove the housing and then taped it up afterwards. I used to see it all the time. gd lk!

[silverlock]

PopsRacer — thanks for that. Helped narrow it down.

The left rear turn signal bulb was OK (first thing I checked!) but was no longer seating as tightly in the socket.

Flushed it out with contact cleaner, used a pair of needle nose pliers to pull the spring contact forward (gently) so that it pushes on the bulb more, and we were good to go. I suspect some solid rally miles, 15 miles of dirt track & a lot of rain at an event in WV didn’t help.

(I also now know a lot more about the external lights & have a useful ground test cable)

[PopsRacer]

nice work!