i have an 85 f150. the brake lights are not working. i checked the bulbs, both filiments are working. i have running lights, turn signals, and hazards, just no brake lights. i am confused as to why i have everything else except brake lights. need to figure out what to do next to figure this out.

 

Near the top of the brake pedal there is a switch attached....called the BOO switch. (Brake On/Off) These fail more than occasionally.

 

Yes, check the switch on the brake pedal. After that the signal goes up to the turnsignal switch. It goes through the turnsignal switch, since the filaments in the back for the signals are the same ones the brake function uses.

 

how do i tell if the boo switch is working correctly or not? also how do i check to see if the turn signal switch is good? i got a whole parts truck so if i need to swap them out, unless they are fairly cheap to replace. last i checked the lights and all that worked on there. how hard is it to swap them over?

 

You'll need a voltage light or meter. There will be 12v going in on one wire and with brake pedal not depressed, no voltage on the wire coming out. With the brake pedal depressed, 12v on both sides.

 

im assuming this is for the brake switch

also how would i test the turn signal switch?

 

i just went out there to look at it and to test them but have no idea what im looking for. can you help me out here with a description and step by step maybe on what exactly im looking for? i have no idea how that system works. thank you

 

If you don't know that, you'd better take it to a shop that does...... this is pretty simple stuff...... Here, try this: http://www.agcoauto.com/content/news/p2_articleid/243

 

Do you have a testlight? If so, take the alligator clip and put it on the negative of the battery. Touch the probe on the positive of the battery. This is what you are looking for. Take the alligator clip off the battery and clip it to a good clean piece of metal under the hood. Then touch the probe to the battery +. The light should light. This is because the negative of the battery is tied to the metal of the truck.

Get under the dash and clip the alligator clip to a good clean metal place under there for the negative. Then find the brake switch on the pedal. Don't push the pedal, and probe both wires. One of them should light the testlight. This is power going into the switch. Put the probe on the other wire that does not light the testlight, and then push on the pedal. The testlight should light up when you push the pedal, and go out when you let up on the pedal. This is the signal going out to the turnsignal switch.

 

thank you, thats what im looking for. just saw a bunch of wires that i have no idea where they go. so the wires im looking for are the ones attached to the brake pedal itself (the switch). just looked at pictures online, so now i know exactly what to look for. ill go test it out tomorrow. should test 12 volts on both sides correct? one side constant while the other only when i push the pedal in.

if this tests good, your saying the next step is the turn signal switch. where is this, im assuming in the steering column. how do i test that? hoping i dont have to take it that far but covering my bases ahead of time.

ill let you know tomorrow if the brake switch tests good.

 

The turnsignal switch is in the column behind the steering wheel. You may be able to get to the wires as they come out of the bottom of the steering column. See if you can take readings while the plug is plugged in. Unplugging it will mess the test up.

You said you had a 85 correct? The brake switch wire is lightgreen. This wire will leave the pedal switch and head over and go up the column. If you can poke the wire, you should be able to push on the pedal and then let up, and get the testlight or voltmeter to come on and off(testlights usually have sharper probes for poking the wire).

The voltage for from the pedal goes up and goes through the switch and onto two different color wires that go to the rear lights IF THE TURNSIGNAL SWITCH IS IN THE CENTER POSITION. These two wires are orange/lightblue and lightgreen/orange.

 

both wires had 12 volts to them, and when i pressed the pedal the voltage dropped to 0 and had a few sparks, than no voltage at either one. thinking i touched metal while i was holding it and blew a fuse. but since both wires had 12 volts, why arent my brake lights on constant? i also noticed that the pedal when not pressed isnt pushing in the plunger infront of the pedal. so im thinking thats why both wires had 12 volts, and that needs to be adjusted. need to check for a blown fuse and also taking the truck in to have the switch replaced since im thinking its bad and its only an 8 dollar part. that way they can adjust the pedal at the same time. also need exhaust work done so ill get that done at the same time also.

am i correct in assuming the switch is bad since it had 12 on both sides but brake lights still dont work? remember the turn signals which run off the same filament work just fine along with hazards. tail lights work also but seperate filament.

and yes it is an 85.

 

You may be looking at the wrong switch. Make sure the wires are lightgreen(I think one is light green with a red stripe). There are other switches, for the cruise control, etc. The one you are looking for is a weird looking thing that rides on the pedal pin itself. It's not mounted to anything, it rides back and forth on the pedal. It's a strange design, but Ford has used it for years on all it's vehicles.

 

Ok ill have to double check it than

 

Franklin this is how I'm testing my brakelight switch, but I have the opposite problem. The switch works when not on the brake pedal at all, it's hard but when I push the spring up I get a reading, I put it back on the brake pedal and press the brake and the circuit won't close . I've tried putting it on different ways.


is there a chance the switch is worn to the point that the pedal won't close it, is there a chance it can be put on the brake pedal wrong.?