1991 Ford F150 headlights

Hi rbguy1,

I would like to confirm 1 thing with you, does the hazard works when headlights are turned on?

After checking through the circuit diagram, there don't seem to be anything that can cause the problem except poor ground or loose connections at the fuse block.

Do the following test with headlight on.
1. power supply to brake switch.
2. Turn on hazard light to see if they work.
3. Test for power output from Turn signal, either Light Green/White (left turn) or White/Ligght blue.

The Hazard lights do not work with headlights on. When I push the brake pedal they still do not work, however the dash light indicator for the turn signal/hazard is dim when the hazard and head lights are on, when I depress the brake the dash light indicator brightens to full strength but does not flash.

Hi rbguy1,

Seems there is not enoough ground for the lights and they are reverse flowing neutralising the power saupply to each circuit.

I would suggest checking the rear groundings at taillights, especially the Black color wire.

I'm not entirely sure what you mean by the grounds, can you explain where and what they are?

Hi rbguy1,

Sorry for getting you confused.

Grounds = earthing points to body (negative)