ot but might be usefull on old tractors

ericlb · Feb 5, 2015

got a 379 peterbilt im driving thats driving me insane,here's the deal the front turn signals have quit working, the truck has had its headlights changed to singles with the turn signal in the side of the light, they did work fine until recently, it still has led turn signals on the mirrors so im still driving it in the county , but i have power to the faulty bulb, the bulbs are new as now, are the sockets, checked with a test light grounded to the headlight mounting bolt, i suspect a bad ground and its being lost thru the tilting hood, not surprising, since it has bushings in the hinges, but,, the test light works, and its a light bulb, so why doesnt the number 57 bulb on the turn signal work when a wire is ran from it the the same bolt the testlight is grounded too, this thing is driving me crazy and i have to get these working!

Jo Bird · Feb 5, 2015

Rather than jumping to the bolt, jump to the outside of the socket with the test light from each post in the bottom of the fixture. You may have a break in the wire from the socket to the bolt or depending on age some wires turn black inside, corrode and stop carrying current.

kansas45 · Feb 5, 2015

Those headlamps need a good ground. As Jo Bird said, check the wires & sockets for power. Also be sure to check the ground wires. A lot of folks crimp or twist the original headlamp wires and cover the connection with electrical tape. This makes a good environment for corrosion to grow.

Guido. · Feb 5, 2015

Hello ericlb,

Take a good TESTED GROUND to the 57 bulb ground side of the socket. Even if you have to get it from the engine. Then from that ground check for voltage at the bulb socket. Either the ground is bad, or power is not reaching the bulb. I'm betting on a bad ground,

Guido.

ss55 · Feb 5, 2015

Try using a volt meter instead of a test light to look for resistance in the circuit. Or take it to a repair shop.

Owen Aaland · Feb 5, 2015

Check the voltage at the bulb with a bulb in the circuit.

If you have a poor connection in the wiring you can have the correct voltage when checking without a load on the circuit but the voltage will drop off when placed under load.

caterpillar guy · Feb 6, 2015

Eric, I have already been through this with the same model truck only mine has the dual headlights. Contact Peterbilt in Finlay OH talk to Rick in Parts. You need to replace the wiring harness from the bumper to the headlight. There is a plug right down by the hinge on the hood.
The number is 419-423-3441. For the dual headlight they use an older model harness and it was only about $35-50 If you use the last six digits of your vin it will tell them what it should have. They will ship to you. I priced the harness in Billings MT one time and they told me 300.00 for the same harness. This was by using the last six.
I could get a test light to light but not a new bulb. The head lights would not go up to highbeam or something also.

ericlb · Feb 6, 2015

going to see what happens today, i ran a separate ground wire to the light housing on each side of the hood, allowing wire length for the hood to go to full tilt, all is working now, but well see what a day of bouncing and jarring does to that, dont know what somebody would assume the lights would ground thru a movable hinge, but thats apparently what it was supposed to do, there grounded for sure now

ericlb · Feb 6, 2015

might be the same folks who assume a trailer will ground thru the hitch ball, it is possible, but not reliable

ot but might be usefull on old tractors

ericlb

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Jo Bird

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kansas45

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Guido.

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ss55

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caterpillar guy

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ericlb

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