Bob - Turn signal and brake light problems #782

[DanEC]

Originally Posted by patrickt

Dan, if you disconnect your trailer relay on the 3-wire "car side," and then turn the car on, and touch the brakes, the RED wire should have a 12v continuous. Take your foot off the brake and put on the left turn signal. The front left light bulb should be flashing and you should get a pulsing 12v at the YELLOW wire. Put the right turn signal on and the right front bulb should now be flashing and you should get a pulsing 12v at the GREEN wire. If this doesn't happen, then there is a problem upstream from your trailer relay -- either a wiring fault or the turn signal switch is bad, or maybe something else. But that's your first diagnostic test. If you can't pass this test, then there's no point in actually removing the trailer relay.

I checked voltage on the red wire coming to the relay from the brake light switch and got 12V when I pushed on the pedal.

I disconnected the leads from the turn signal switch and got these voltage readings.

Turn signals off: 1.5 V left side and 1.3 V right side.

Left signal on: 12 V left side and 1.6 V right side

Right signal on: 12 V right side and 1.9 B left side.

With everything hooked up I get peaks of 9V and lows of about 1.5V with the flasher flashing on the left side. From memory that is what I found to be the case last year when trouble shooting a front turn signal.

With the exception that I don't know if some low voltage bleed over through the turn signal switch is normal or not, it looks like the turn signal is OK.

Comments?

Dan

[patrickt]

And the brake lights did not work a few days ago when you had everything wired up? If so, then the relay is clearly suspect since you're feeding the relay a nice clean 12v when you hit the pedal.

[patrickt]

Unless the voltage leak to the turn signal feeds to the relay confuses it to such an extent that it just shuts down. You could test that by just hooking up your brake light feed to the relay, then hit the pedal and see if your brake lights come on. If they do, and then when you hook up your other two wires, they then don't, then it's the voltage leaks that are confusing the relay.

[DanEC]

Originally Posted by patrickt

Unless the voltage leak to the turn signal feeds to the relay confuses it to such an extent that it just shuts down. You could test that by just hooking up your brake light feed to the relay, then hit the pedal and see if your brake lights come on. If they do, and then when you hook up your other two wires, they then don't, then it's the voltage leaks that are confusing the relay.

Patrick - If I unplug the turn signal leads and press the brake pedal I sitll get a brake light on only the left side.

[patrickt]

Originally Posted by DanEC

Patrick - If I unplug the turn signal leads and press the brake pedal I sitll get a brake light on only the left side.

Assuming the circuit to the right brake light is good, then the relay is the only thing I can see it to be.

[DanEC]

I think I solved the mystery today. I got my new relay and started taking the old one apart from the fuses. The green wire on the trailer end practically fell off the crimped connector - apparently the wire was partly severed when the connector was installed and finally broke or it's been flexed a lot as I worked on installing everything and broke. The green wire feeds the right side which is where I had the problem. So the relay is probably good and I may hang on to it for a spare. Should finish crimping and soldering the connections tomorrow.

[patrickt]

Good job. Yep, always solder your crimps.

[1795]

Thanks for the posts. I have been following them diligently, but have not offered any advice because the electrical end is where my knowledge and experience breaks down. It is always important to test every connection for weakness and visually inspect wires for damage. Nice job Dan and excellent advice Patrick.

Jim

[DanEC]

Unfortunately I could not see the break due to the heat shrink insulation. It was only when I cut into it to make sure there was a spade connector in there to unplug from the fuse block that I saw it.

Thanks