Need help with electrical issue.
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2nd Gear
Joined: May 2024
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Need help with electrical issue.
I have a 78 F100 Manual transmission. Recently purchased to fix up with my son for his first car.
The headlights low an high beams are working. Blinkers front an back ,Tail lights, break lights, backup lights, a cab light are not working.
Replaced the blinker switch, checked fuses, a the grounds at the taillights. Lost at this point any help appreciated!
The headlights low an high beams are working. Blinkers front an back ,Tail lights, break lights, backup lights, a cab light are not working.
Replaced the blinker switch, checked fuses, a the grounds at the taillights. Lost at this point any help appreciated!
Last edited by terry87309; May 20, 2024 at 09:00 AM.
Lead Driver
Joined: Jul 2017
Posts: 9,606
Likes: 1,175
From: San Jose, CA
A few things could be related, or they could all be separate issues.
Given that you just picked up this truck, and someone could’ve neglected it for years, they could easily be separate issues.
I would start at the front turn signal/running lights, or rear turn signal/running lights. Pull the lenses or housings out, and check for power with voltmeter at each of the terminals, with the headlight switch in the first position.
No sense in draining the battery needlessly while you’re puttering around, so the first position on the switch should work.
There is no headlight switch fuse, and we know the headlights are working, so you will have power to the headlight switch. Power for the brake light switch comes from the headlight switch, so check one of the wires coming into the brake switch. One should have power all the time, while the other only has power with the pedal depressed.
But you could be dealing with something as simple as burned out bulbs or bad grounds.
I think, not personally having run into this issue with my trucks, I don’t have a known common denominator.
Given that you just picked up this truck, and someone could’ve neglected it for years, they could easily be separate issues.
I would start at the front turn signal/running lights, or rear turn signal/running lights. Pull the lenses or housings out, and check for power with voltmeter at each of the terminals, with the headlight switch in the first position.
No sense in draining the battery needlessly while you’re puttering around, so the first position on the switch should work.
There is no headlight switch fuse, and we know the headlights are working, so you will have power to the headlight switch. Power for the brake light switch comes from the headlight switch, so check one of the wires coming into the brake switch. One should have power all the time, while the other only has power with the pedal depressed.
But you could be dealing with something as simple as burned out bulbs or bad grounds.
I think, not personally having run into this issue with my trucks, I don’t have a known common denominator.
Tuned
Joined: Apr 2023
Posts: 363
Likes: 108
cab lights as in the ones on the roof? those should share the firewall ground from the engine to the firewall and the main power wire goes through the A pillar up from the headlight switch unless they are aftermarket and have their own switch (common) i don't know when ford switched, but for a lot of years the lights were not fused. there was a built in circuit breaker in the switch itself.
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