hey everyone, just recently picked up an 87 f250 with a 5 speed 302 and 140xxx paid 2000 for it, pretty solid but i am from for vermont and its a vermont truck so its not perfect body wise, I have discovered a wierd problem and i dont know where to start, when my headlights are off both my blinkers work fine and the dash lights blink accordingly but when i turn my headlights or parking lights on the blinker idicators on the dash stay lit as well as the blinkers outside, and when i hit the turn signal the blinker lights on the dash just dim a bit, and the blinkers dont flash, im not sure what to check or do. thanks for the help.
-Ben

il try to get some pics posted soon

 

i have the same exact problem. i noticed tonight that with my headlights on, my diectionals blink slower than normal. so i got out and checked and noticed that with either my left or right directional on, the back of the truck shows my hazards flashing. also, i noticed that my backs weren't flashing with my fronts at the same time. however, when i turn my headlight switch completely off, everything works fine. so, i'll start there, tomorrow i'll install a new headlight switch. the only thing i cant figure out is, "do any of my directional wires happen to run through my head light switch harness"?

 

Either switch or flasher module in fuse block.

 

You might have a bad ground on your headlights, so it is somehow using the ground for your directionals and activating your flasher on the fuse panel. Did you check all the fuses? Just a guess, good luck. If you remove the flasher and your headlights dont work then it probably isn't the headlight switch. You may also just need a new flasher, Mine started doing funky, unpredictable things before it finally quit. It would just stay on, it would blink slow, then it would blink fast, then it just died.
One other thing to consider; do you guys have alarms on your trucks? they are wired into the headlights and directionals as well. If you find a 9 volt battery somewhere under the dash replace it.

 

nah, no alarm for me. however, i think i did pull my flasher relay and i think thats when my driving lights on the rear started working again. well, that will be first tomorrow. thank you

 

alright sounds good il check that fuse and also see what happens if i pull the blinker bulbs, thanks
-ben

 

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i got it. i tried replacing the relay today, no success. i pulled the taillights and checked the contacts. something was crossing over somewhere, with the lights on, brake pedal pressed down, and with the directional on caused my driving lights to blink. it looked like my hazards were on. i replaced my headlight switch and congratulations to me. solved the problem. the switch was 15.99 at pep boys. the only thing that sucked was that i needed channel locks to rip out the old switch stem that the **** is attached to. good luck. you're looking at a 15 min job including a cigarette break. lol