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Brake lights always on

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Old 11-24-2012, 07:14 PM
mnkeeking mnkeeking is offline
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Brake lights always on

Need help. Have a '68 F100 flareside. My brake lights are always in the "brake" position, meaning it looks like I'm standing on the brakes. This only happens when I also have the lights on, even in the parking light setting. So I spent the last two days re-wiring from the fire wall to the tail lights. Found some mushy 4-wire connections in the bay, fixed them too. Put a new fuse in, turned on my lights, turned my key to ON. Had turn signals at this point. Hooked up my brake switch with my finger on the plunger keeping it off. Let fly on the switch and the 20A fuse blew. Began chasing wires thru the dash, but it's getting dark and I can't think straight after chasing this ghost in the machine. I read the other posts and someone suggested the turn signal switch. Is this correct? With the blown fuse I have ON brake lights, none if the key is off. Hook up the brake switch, and either blow a fuse or start a fire if I try to jump or tin foil it. I need help, this is driving me crazy.
Thanks,
Joe
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Old 11-24-2012, 09:41 PM
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I would investigate the turn signal switch. Maybe unplug it and test the wires. With no power, see if you get any leads to go to ground with an ohm meter.

There are only 4 wires going to the rear of the truck for the lights to function, so if you fixed that already, then it is likely inside the truck.
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Old 11-25-2012, 05:47 AM
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Joe to add to FT, have you done any work on the electrical anywhere on the truck?

You might want to check at the master cylinder, with the ign switch on, one wire should be hot the other not, if both are hot the brake light switch is bad, allowing current to pass at all times.




John
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Old 11-25-2012, 06:33 AM
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Quote:
Originally Posted by mnkeeking View Post
I have a 1968 F100.

Hooked up my brake switch with my finger on the plunger keeping it off.
If the switch has a plunger on one end, it's round and has threads below the plunger.

This switch was used on 1969/72 F100/350's only. So, you either have a 1969 F100, or someone changed the brake pedal.

1967/68 F100/350 uses a totally different switch. Pushrod has a hole in it, switch (it's rectangular) has two holes, pushrod fits in between them.

Bolt passes thru switch-pushrod-switch then thru hole in brake pedal, nut retains it.

Post the last 6 digits of the VIN, this will verify the year.
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