My truck is an electrical nightmare. Here's the story. When light switch is OFF everything works fine except when I press the brakes my front turn signal lights and roof marker lights light up with the brake lights. When my light switch is ON my brake lights are stuck on, left rear turn signal works, right rear doesn't, roof marker lights and front turn signal lamps get brighter when brake is applied. And sometimes when light switch is on everything works fine BUT I have no rear running lights (tail lites). AHHHHHHHHHH!!!!!!!! I've been pulled over 3 times and next time I get impounded. HELP ME PLEASE!!!

Thanks

 

Oh ya I forgot....'81 F150 4x4

 

OK, I had almost the exact same problem on my Cougar. Best part is, it's an easy fix.(cheap too). Just change out both of your taillight bulbs. What I believe has hapened to you is that the two filiments in one of the bulbs have shorted together. That is why you are getting a crossover between the Brake/turn system and the park lights. Go try it, let me know if thats it. I tore half my dash apart trying to figure mine out when all it was was a bulb!

Hope that's it, let me know !

 

Already changed the bulbs! Did nothing.

 

You most likely have some electrical ground problems . Electricity will always take the easiest route to ground if it cant ground like its supposed to . Using a wiring diagram see what is common to all the affected circuits & go from there .

 

OK, Well I think the problem is the same, It's just not in the bulb. I would pull the right light, and start following the wires back under the truck. If the insulation is crusty and starting to come off, then the park lgts could be shorted to the brake lights, creating a crossover. Also, is there a trailer light plug? If a wire came apart inside, that could cause your problems too.