Turn signal short? F250 1987

Asked by Fred Jul 01, 2022 at 05:10 AM about the 1999 Ford F-250 Super Duty XLT 4WD Extended Cab LB

Question type: Maintenance & Repair

1987 Ford f250 extended cab lariat 4wd with 460
carbureted auto. My passenger side turn signal indicator
dimly lights up without a relay with no exterior signal lights
on passenger side when function when headlights and or
running lights are powered on. Turn signals and indicator
for passenger side function correctly without headlights or
running lights . There's also a slight amount of  power
going to the dash illumination running lights when
passenger side turn signal is engaged. There's no relay or
exterior lighting but a dim indicator. Driver side turn signals
function normally in all situations. Just replaced both front
turn signal indicator sockets and cleaned grounds. Baffles
me to the indicators will work until exterior lighting is
activated and cannot find in a wiring schematic a direct
link. Operating on Independent circuits. Any clues? Scooter

4 Answers

40,015

everything needs a ground , you need a multi tester to see what has power/ground and what don't

310,255

Still sounds like a grounding issue. There are grounding points all over this truck, in the front, in the rear, battery to engine, engine to frame, frame to body. On my old Ford truck I ran some ground straps from frame to body.

310,255

I just remembered something I ran into back in the day, to make it short, check the 4 way switch, it might not be fully seated in the off position causing a feedback or loss of proper current, cycle it a few times and make sure it works as it should. Then check everything.

I found the fix to be with the driver side rear tail light bulb. It had an internal short across the running lights and turn signal brake lights circuits. It produced approximately 5 volts of power feeding into the running lights circuit causing the flasher relay circuit to safety and putting low voltage into the illuminated dash running lights. Creating a closed low voltage circuit between signals and running lights produced questionable circuitry wiring schematics as they are both independent circuits until a bulb has internal voltage bridging. Independent circuits are always dedicated circuits until introduce to a light bulb. Simple fix confusing diagnosis. Thanks for all your feedback. Scooter

Your Answer:

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