1991 Ford F-150 headlights

RBGUY1

MEMBER
1991 FORD F-150
6 CYL
2WD
MANUAL
160,000 MILES

My 1991 f150 when the headlights are on, the turn signals and brakelights do not work. When the brights are on, the turn signals and brake lights work but I have no tail lights. I have replaced the headlight switch and head light switch connector. The turn signal switch I replaced but that did not solve the problem so I returned it.

5 Replies

KHLOW2008

MECHANIC
41,814 POSTS

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.

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Friday, October 17th, 2008 AT 8:40 AM

RBGUY1

MEMBER
2 POSTS

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.

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Friday, October 17th, 2008 AT 11:00 AM

KHLOW2008

MECHANIC
41,814 POSTS

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.

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Friday, October 17th, 2008 AT 11:18 AM

RBGUY1