Thread: 1978 F150 brake light issues

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Hey everyone, I've been gone for a long while but I have been on deployment and just got home. So I bought a f150 before I left and I was driving it around the day I got back with no issues. I parked it overnight and the next day it wouldn't start, I got it jumped and realized that my brake lights are stuck on. I replaced the stop light switch at the pedal with no result. I also removed the trailer light plug that the PO shotly installed, once that was removed my drivers side brake light went out but not the passenger. The drivers side now will not light when the brake is depressed, nor will it blink with the blinker. The passenger side just goes out when the right blinker is turned on. I went through the rear light wiring harness for shorts and ended up replacing all the wires and remaking the entire harness but no result in any of the issues. Has anyone seen this before? Any help would be great.

brake lights and turn signals fed tru the turn signal switch

Turtle, it has been my experience that once a wiring harness begins going South, it's best to yank the whole mess out and completely re-wire it with a whole new system. My very best advice to you is to buy this FACTORY electrical schematic from Faxon and begin purchasing components.
1978 Ford F100 F150 F250 F350 Foldout Wiring Diagram Original
It's also possible that one of the aftermarket suppliers can sell you a complete replacement wiring harness that you could plug and play. Here's a roster of manufacturers....
Automotive Wiring Harnesses

and some other websites....
CLASSIC & MUSCLE CAR WIRING HARNESSES and ELECTRICAL PRODUCTS
Wire Harness Manufacturer, Wire Harness Assembly,Design,Electro-Mechanical,Prototype,Custom Manufacturing GA
https://www.ronfrancis.com/
Painless Performance
American Autowire: Wiring Harnesses, Accessories, & Parts for GM Restoration, Modified Restoration & Custom Street Rod

and let's not forget my number 1 pet peeve, lack of proper grounds. It is not possible to have too many grounds on a vehicle, so grind down to bare metal and ground the motor to the frame and the frame to the body with new ground cables.....
9" from NAPA...http://www.napaonline.com/Catalog/Ca...577_0459880039
13" from NAPA...http://www.napaonline.com/Catalog/Ca...559_0187600146
18" from NAPA...http://www.napaonline.com/Catalog/Ca...465_0459879965

When installing grounds, use star washers that dig into the base material of both parts and lock everything together....
http://www.randyray.com/TMC/images/R...StarWasher.jpg

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Grounds are indeed good.

But the only way you can really know where the problem is, will be to track the voltage.

Get a good multi meter, and a 20' length of wire. 16 AWG stranded would be my favorite, but it doesn't matter.

Put one end securely to the negative battery cable, and the other to your negative lead on the multimeter. I suggest alligator clips.

Now, using a schematic, trace the voltage, from brake light switch all the way to the bulb.

There are doo dads specifically made to pierce the insulation, makes it easier. Or a fine sewing needle works too.

Good luck

Techinspector1- yeah I ended up rewiring the whole rear light wiring harness with new grounds and everything with good heat shrink connectors and new sheathing. Next I'll just have to try firebird77's idea with the long negative lead and trace the source. Thanks everyone

Did you replace the sockets? They have been known to be a source of trouble as well.. I second the ground concerns.

No I haven't replaced the sockets yet, I should though since they are fairly cheap