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1980 - 1986 Bullnose F100, F150 & Larger F-Series Trucks Discuss the Early Eighties Bullnose Ford Truck

Brake light question

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Old Aug 11, 2007 | 03:26 PM
  #1  
ladderdawg's Avatar
ladderdawg
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Brake light question

My son's 1986 F250 has a brake light issue.

When I turn on the light switch, the brake lights come on. When I hit the brakes, there is no difference in brightness. The brake lights work just fine when the headlight switch is off.

Any ideas on this?

Dan
 
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Old Aug 11, 2007 | 03:45 PM
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Chances are a short in the switch or wiring that feeds that circuit. It is supposed to receive a lower amount of voltage for the normal running lights then receive full voltage when the brakes are hit.

I took a look at my schematics and I believe it is most likely a bad switch. At the very least that is the easiest thing to try.
 
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Old Aug 11, 2007 | 05:01 PM
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Do the turn signals and hazard lights work normally with headlights both on and off? The taillight/stoplight bulbs have two filaments (small one for tail, the large one for stop/turn/hazard). The bulb itself has three electrical connections, one for stop, one for tail and the third is the ground (bulb base shell) common to both. This is the only common point for the two circuits unless somebody has tried to add trailer lights, etc. and got the wiring crossed up. One thing to try: remove the taillight/stoplight bulbs an make sure they are reinstalled properly and are the correct number. It is possible to force them into their sockets with the wrong orientation which can cause some strange symptoms.
 
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Old Aug 11, 2007 | 11:08 PM
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Yes, when you turn the headlight switch on, the brake lights should not come on. The smaller filament in the bulb should come on, which is the taillight filament. This circuit is the darkbrown wire, and it feeds both taillights and the license plate lights.

The brake lights are the same as the turn lights, and these are different filaments in the bulbs, and there are two seperate colored wires running to the rear for the left and the right.
 
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Old Aug 12, 2007 | 11:44 AM
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Thanks for the help!
 
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Old Aug 12, 2007 | 01:21 PM
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From: LaFollette Tn
Hi Piffery1.Does`nt his truck still use the 1157 bulb?If so,there are only TWO contacts on the bulb base.IIRC,the bulb grounds through the copper part of the bulb to the socket.

Leo
 
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Old Aug 12, 2007 | 02:02 PM
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Woodbutcher05, Reread my post. I said there are 3 connections, one for each filament (total 2) plus a common one (shell) for ground.
 
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Old Aug 12, 2007 | 05:00 PM
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From: LaFollette Tn
Yep,done goofed.Heat has me half asleep.

Leo
 
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Old Aug 12, 2007 | 09:00 PM
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by any chance has someone wired in trailer wiring if they have there could be a wire hooked up wrong if it does try cutting the trailer wiring off and see what happens
 
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