What would cause this?

[Razorback_Fan]

Ok I know that a hundred things could cause this but all info appreciated. Turn signals and brake lights do not work. As soon as you step on the brakes the fuse blows this also happens as soon as you use the turn signal. Any ideas? I got a feeling the signal switch is causing the turn signal problem but curious on what would cause both fuses to blow.

[bpmcgee]

Okay, the stupid answer to your question:

There's too much current going through the fuse, and that causes it to blow.

I know, I know, not very helpful. But, if you think about it, maybe it leads somewhere.

Something is wrong which causes an over-current problem only when you use the switch. Is there current flowing through it when the switch is off, which causes it to go over when you use them? Or is there a short someplace which causes too much current to flow only when the switch is used?

Could the turn signal switch be bad? Both the brakes and the turn signals are wired up into it for the hazard light function.

Sorry, that's all I can think of,

Brian

[solidaxel]

Look for a SHORT to ground, or a pinched wire, follow the wire loom from the firewall to the rear and try and isolate it from the front or the rear lights. Keep looking you will find it !!

[TROYLV]

you are on the right track solid axle. the wire to the brake light runs from the turn signal fuse thru the brake switch to the the turnsignal switch in the column. then down the column to the bulkhead connection out to the wires back to the rear brake/turn lights. also goes to the front ones, but your brake light switch will not cause them to light up. designed that way in the turn switch. sooooo if it does it with the brake applied and or the turn switch then it is in the rear part of the wiring. could be anywhere from the turnswitch, down the column to the rear wires. again solid axle is correct, a bad ground will cause high resistance which causes high current. so check the grounds also.

[TIMSPEED]

Razorback,
Trust me, there's a SHORT! I COULD NOT figure out why my B/U Lap fuse kept blowing, which in turn would cause my blinkers not to work. So, I remembered that I *SORTA* burned my wires when I cut off my bumpstops...so, I ran a few new wires, and good as new!

[Razorback_Fan]

How can I check the switch to see if it is bad? I had a mechanic adjust the switch because I could not dim my headlights after that is when the problem started.

[phantom dually]

Use a test light and put the clip at a 12v source. Probe all of the brake light wires at the dash. The wire that makes the test light come on is the one being grounded. Most tailights ground at the rear of the truck therefore you should only have a few wires that get 12v of power. I would suspect the wire that is for the brake light only. You said the lights work fine until you hit the pedal so its not the running light wire. Try to turn the signal on only and eliminate each wire one by one. Find the one thats grounded out and trace it down and repair as needed. Start in the rear and look for bare wiring. Good Luck

[wHATANERD]

Is your truck wired for a trailer Harness, I've seen some bazzar wiring behind the lisence plate, and if tape has came off it could easily cause a short

[Bobs76]

Trust me it is the turn signal switch. They do go bad, My dad has a 72 that did that, I heard from a mechanic that that is what it does and sure enough that fixed the problem.

[phantom dually]

In this case unplug the harness then probe the wires at the harness plug. Check for a ground.