OK, here's the deal, I put led bulbs in the rear of my 1984 f150. with help form here, we figured I should put resistors in line to make the bulbs flash, which worked perfect. Now I put the truck cap on and hooked up the third brake light to what I think is the stop light wires, on the drivers side, at the same place I put the resistors in line. In the daylight with no parking lights on the third brake light works fine. but at night, when I run the headlights and parking lights, the third brake light flashes with the blinkers? ( At night the left side where I hooked up the third brake light flashes faster than the right, but in the daylight they both work the same?) what did I do wrong this time? this is like a game of chess, and I am bad at chess...and electrical. the resistor is hooked up to what looks to be, the larger wire which is green with an orange stripe? ( hard to tell with all the rust proofing) and the black ground. so is the third brake light. I did not use the slightly smaller brown wire, nor did I test it as the wire I used flashed when tested. why is the center third light flashing? Once again, I bow to your collective wisdom, and seek guidance. Thanks in advance, vic

 

To my knowledge, the third brake lights didn't come from the factory until sometime in the 1990s and if you want one, you'll have to run your own wires for it.

I'm too lazy to look in the electrical manual right now but I think you're using the RH brake/turn signal wire.

The brown wire is the marker lamps everywhere - all four corners, rooftop lamps (if equipped), headlight-on buzzer on some vehicles (if equipped). This uses one filament in the bulbs.

The brake & turn signals share the other filament in the bulbs and have separate wires.

You'll need to run a wire from the brake light switch to the rear if I'm not mistaken.

 

the third brake light is on a1985 bed cap, by leer. so I have to run a separate wire all the way from the switch? you can't use the stop/flasher wire in the rear driver side? these little jobs just get bigger and bigger...Oh well, thanks ctubutis

 

No because the wire for the rear brake lights is also the flasher wire to the rear, when you turn the signal on the flasher cycles the power thru the brake light wire to the respective side

 

OK, took a look under and it seems the last owner ran a line back for a trailer hook up. looks like it goes all the way up front. when I have time, I'll see if it is still live to use? as it looks like he may have had a trailer brake on this at one time? not there now though... Thanks, again, vic