I'm having some issues with the interior lights/blinkers on my '71 Mach 1. It's never been fully restored and I'm just now trying to finish everything. I replaced the fuses, but the 4amp in the third circuit keeps getting blown, and I can't figure out why. It powers the blinkers and the interior lights, both of which don't work. It's not my flashers, and all other contact points but the third one are hot. The third isn't hot in either place. I think it might be something under the hood, maybe outside the firewall? I really have no idea and I'm not fantastic at electrical stuff so any ideas anyone might have would be greatly appreciated.  

check the grounds at the front turn signal housings and up the wires to the core support...

pull the bulbs with the power off and clean the sockets with a 1/2" copper tube cleaning brush...  then use some electrical contact grease out of the little packets next to the cash register at many auto parts stores...

do the same with the tail lights....


when the front turn signal lamps are not properly grounded... they feed back through the turn signal indicators on the dash...

what you will get is when you turn on the headlights.. one or both of the turn indicators on the dash board will light up... when you turn the directional signals to that side.. the dash indicator will go dark then seem to function properly....


be sure that you have working flashers... there are 2 on that car... i try to use 552 flashers instead of 224 or 536's or what ever number is in there...   552's will flash one or 6 bulbs...  the others will only flash the number they are designed for...

when the tail lights circuts  have bad grounds... the brake lights work opposite from the way they should...

so with the tail lights on... one side may be dim... when the brakes are applied... and the brake light  circuts get powered up one side goes out and the other get bright...

this tells you that ground wires are important.. they are half the circuts to light the bulbs....   by the way... for everybody reading... electrons from from (-) to (+)...