wally74

Hello all,

My Cutlass 350 1975 has a strange electrical thing.

It has something to do with the taillight I think....


With headlight OFF the turnsignals on the front and tail are funktioning.

With the headlights ON only the rightside (passengerside) is working BUT then the bulbs on the tail are flashing after eache other.
The frontside is working only at the PS (same as the tail)

The hazardlights are okay when the headlights are ON.

Whith the headlight ON the brakelight on PS is working double so bright as normal and the DS brakelight is dead.


I thinks it has to do something with a bad ground or so.., but because I'm a electrical I ask you guys for some help and advice.

Btw
I hope you can understand (read) my "english"discription of this problem

Wally

oldcutlass

Do the brake lights work, because what your describing is a bad lamp or possibly a contact problem in your lamp sockets creating an open circuit with your brake/ taillights.

joe_padavano

That, or a bad ground. The 1157 bulbs have two filaments with a common ground. If the ground is bad, the circuit will find a ground through the other filament. This works with the lights off. With the lights on, that other circuit has +12v on it, so there is no ground.

svnt442

I'd take a close look at the tail light sockets. That was a big issue with these cars. I had two 75's and a 76 and all three of them had issues with the tail lights.

wally74

Thanks.

When the headlights are ON the brakelight on the ps shines for two while the other brakelight is dead.

Also,
If I pull one bulb out the socket then there's a very slow turnsignal in the remaining bulb. (also the front blinker) When I put the bulb back, both bulbs shine very weak.

Joe;
How can I test this bad ground?


Wally

wally74

hi there,

a small update:

3 wires in the taillightsocket; brown, yellow and black.
when I pull black ( ground) out of the socket the bulbs are still glowing or with the headlight OFF, flashing.....
There is 10V on brown and 4V on the yellow wire.

Randy:
Where do I've to look for?
I looked at the socket and there was nothing strange for me to see.
That dosn't mean anything because I don't know how a perfekt socket should look like.

wally

Rocket Richard

Just general advice:
If you don't have a service manual for your car you should get one. Wiring diagrams are your friend. I'm no expert, but when I have an electrical problem I use the wiring diagram to see where all the wires go. I can check to see if the juice makes it from one end of a wire to the other, and check all connections and make sure everything is clean and the way it is supposed to be. Sometimes I use the wiring diagram to make a simple sketch of the circuit I'm working on. It makes it easier to look at, and I'm not draging the manual with me as I'm crawling around the car looking for wires.

For problems with lights I guess I generally work backwards from the light bulb to the fuse panel checking all connections and continuity in the wires. There are obvious things like a dead battery or a blown fuse to check too.

Volt meters are good to check if a wire is carrying juice from one end to the other, or if the juice is spilling out somewhere because the wire is shorting out. You can also use them to check that your grounds are good. A test light will work for these checks too.

Hopefully this helps you.
-Rich

Edit: oh for testing that bad ground at the front, use a volt meter to read the resistance from the battery negative terminal to the ground connection on the bulb socket. Or use a test light: connect one end of the test light to the battery positive terminal (or a good source of 12V) and connect the other end to the ground connection on the bulb socket... if the ground is good the light will be nice and bright.

svnt442

Pull the sockets out and pull out the bulbs. Check for any signs of corrosion or rust inside the sockets.

wally74

mission completed!
I found the bad ground....at least...

thanks for your advices.
Wally