Going to be wiring the horn to the breaks of a 94 Jeep, so when he brakes the horn goes off as a gag. He's got a 4 pin trailer plug, and i thought i could just tap into that intead of going into the break light itself. At my first attempt the horn made a low noise and i blew the brake light fuse (i may not have had a good ground coming from the pin), anybody ever done this, got any tips?

Ive heard it could me more complicated then that, crap about needing a relay and such...

 

Clearly the horn + brake lights takes more amps than the brake lights alone.

Temporarily insert a higher amp fuse into the brake light slot.

 

I can already smell a disaster ahead...

 

I agree, which is why I was a little reluctant to respond.

I hope this is not on a street driven vehicle. Oh, and a fire extinguisher might come in handy, lol.

OP might want to consider another prank with less chance death or dismemberment. The possibilities are endless.

 

Yea thats why i was asking, blowing a fuse is one thing, but i dont want to fry his wiring.

 

you need to do the relay method. you need to use the brake light (or brake switch) as a signal wire and have a 12v live wire to the relay

 

can i use the green or brown wire from the 4pin trailer wires as the signal?

 

Yeah you should be able to use the 4 pin trailer wire as the signal because that will just be turning on the relay. So it shouldn't blow any fuses doing it that way because all you'll be doing with the signal wire is powering the relay coil which doesn't use that much power. Then all you have to do is run power to the relay that you will use to power the horn when the relay is activated.

 

brown wire is park lamps last I checked. green and yellow are left/right (i forget which order) stop lamps which should be same as brake.

 

In trailer wiring, brown is the running lights. Yellow and green are the turn/stop lights.

 

sorry, meant to say yellow or green. So i went a got a 40amp relay hooked it all up, and worked like a charm...thanks!

 

You are devious! I like it, be sure to get some pics or even better video!!!!

 

wait! before you juice up the 12v signal going to the horn circuit with a relay....its a high probability that the horn wire under the steering column is a negative trigger...basically sits at 12v and goes to ground when activated. the brake is obviously 12v trigger, so you would need the relay to change the voltage from 12v to ground in order to activate the horn relay.

for a 1994 jeep wrangler, the horn trigger is black/red (-) at the steering column, and the brake switch wire is white (+) at the brake switch!

the relay would go like this......85 to ground, 86 to the brake wire, 87 to ground, and 30 to the horn wire.

what i did once to my old manager was wire up an alarm siren...he had a hilarious drive home lol

 

nice, its already been done and worked, but i wired like said above, but straight to the positive side of the horn.

 

ahhh nice lol......prob scared the crap outta him lol