Technical Fuse pops every time brake is pressed

I was wondering if someone could help me figure out this short in my 1950 Ford Shoebox. 12v. I have a newer wiring harness and cant imagine it having exposed wires anywhere. I have gone over the entire brake wiring.

Can the brake switch cause the power to grind somehow?

I just got a new brake switch and it worked fine for several brake pumps and then boom it pops them instantly everytime the brake is pressed.

Any way you can think of to diagnose and eliminate? Headlights and tail lights work fine it's just the brake light fuse that pops immediatley when brakes are pressed.

Thank you.

Blake

 

Chech the bulbs and sockets.
Elimination process

 

The fact that the fuse doesn't blow until you hit the brakes says that the hot side of the circuit is probably not at fault. To test for the switch unplug the terminal and jump it with a wire, paper clip or cotter pin. If the fuse doesn't blow it is probably the switch. If the fuse blows it is probably in the wiring to the stop light bulbs or a shorted bulb. If you have dual contact bulbs try the turn signals as they generally use the same wire and side of the bulb as the stop lights

 

Remove your brake light bulbs, and hit the pedal. If your fuse stays intact, replace your twin filament bulbs (the right way round), and try again. If this still blows the fuse, you are putting a short to ground when pressing the pedal.

 

It appears that the fault should lie somewhere after the brake light switch if the fuse doesn't pop without hitting the brakes. After the brake light switch, the circuit goes to the turn signal switch before going to the lights in the back. You need to check all this.

 

To save money on fuses, disconnect the wire from the brake light switch, and connect it to an ohm meter. Connect the other side of the ohm meter to ground. Measure the resistance. See if it changes when you move the turn signal switch, or wiggle wires, or take out light bulbs, etc. With the bulbs in the circuit, it should measure a few ohms. With the bulbs out, it should measure infinite. If it's shorted somewhere, it will probably measure less than one ohm (depending on how good your meter connections are, etc)

 

Yep .... take the bulbs out and try it.

 

Blake84, I may be misreading your post but I'm getting the idea that your problem started after you replaced the brakelight switch. If this is the case I'd bet it is the switch causing your problem. Is it an hydraulic switch or mechanical? I've seen lots of trouble with hydraulic switches, but only one ever shorting to ground. If I were you I'd disconnect the switch and jump across the wires and see if it still blows the fuse.

 

Remove the fuse and connect an old head light across the fuse terminals when the short appears the light will light up saves blowing fuses.

 

I had another thought. Check that you didn't mis-route the wires when you replaced the switch. They could have become pinched or chaffed causing the short.