Have a 86 F150 flatbed 4wd with the 300 inline 6 with the 4 speed tranny, her names Clementine. Recently noticed that with the headlights on the passenger side rear tailight stays bright as can be like the brakes are applied which causes the blinker filament to not be noticed when its blinkin all you see is a light pulse. The driver side has no problem. The brake light comes on when applied and goes off when brake is released. and everything cooperates when the headlights are off. Whats the problem here?

 

Those kinds of symptoms... dim lights etc.... is almost always caused by a bad ground somewhere.
The circuit then seeks its ground through other bulbs etc.

 

Yup. Track the ground from the bulb back to the connector thats near the drivers rear tire. Squeeze it between your fingers, stretch it some . Its got a kink or broken wire somewhere in there or make a new ground.

 

How bout if i just cut the grounds outta the bulb n ground it right there to the frame

 

That can work just fine. But not really the best. You should have 1 ground from the connector at the rear wheel to i think a connector near the bumper. Been awhile since i was under my 86. There the ground splits and goes to each bulb. If its only your brake/turn light its fairly easy to find. You may even be able to cut and strip the break and use a butt splice to reconnect it.

 

Here is the connector. The orange and the green are your + wires. Black is your reverse lights. Brown is your grounds.

 

Another

 

Thanks ill have to look into it a lil harder Im in no hurry to fix it just tryna fiqure it out nothin is grounded on this truck. it has been stripped of all the emissions n smog stuff. electrical is back to basics but the idiot didnt reground anything. but got a broken shock n someone stole the front driveshaft at lowes so theres more $

 

Hit a junk yard for the front shaft. Should be a dana 44. Fresh u joints and you should be good for under $50.

If you need a wiring diagram lmk. I can snap a pic of a schematic from a haynes manual.