I just bought a 1986 F150 4.9L. The brake lights don't work, changed the brake pedal switch, verified bulbs as good and am looking for a wiring diagram to trace the wire. I've looked at Hayne's and Chilton manuals, but they are both wrong as they show the 86 years as being EFI and the 4.9L was not. I'm also in need of one as the A/C is not working and the A/C drier does is does not have it's connection. I cannot see where it is and grabbed one from my local pull it place, but no sure where to splice it into the wiring harness. Please let me know if you all know where to find one or have any advice. Thanks!

 

302 trucks were fuel injected in 85 and 86. They try to put the diagrams that will be the most useful to the majority of the people out there. If you want a real diagram for your truck, you can look on ebay or go buy one at Service Manuals, Owner Manuals, Wiring Diagrams, Service Bulletins - Helm Incorporated.

I believe this diagram from Autozone should match up mostly to your truck. The lower diagram shows a computer like you should have on your six.

 

Thanks for posting and sorry for my ignorance here, am trying to learn and figure this wiring out, but would the "Back up light" be the same wire for the brake light? The lights going to the brake lights are pink and black that's why I'm thinking so, but wanting to verify.

Also, do you know where the 'Low Brake switch' should be physically located on the truck? I'd like to test this to make sure it's good.

Any and all help is appreciated as I'm wanting to learn this truck inside and out to get it working properly and keep it running for our family vehicle. Thanks again for posting this!

 

No, not the same. The black/pink are the backup lamps (physically separate bulbs) and the tail & brake/turn-signal lamps are green and orange, while the parking lamps (different filament in the same bulb) all share a single brown-wire circuit.

 

So to be sure that I understand correctly:

Backup lamp = 1 bulb; black/pink wire

Tail/Brake/Turn Signal/Parking lamp = 1 bulb, different filament's; green/orange wire

All of them[Backup, tail, brake, turn, and parking] are on the same brown-wire circuit, is my understanding correct?

Thanks for setting me straight

 

Kind of
Black/pink splits to 2 wires-1 to each side
Orange/blue is right signal/brake
Green/orange is left signal/brake
Brown is common power for all parking lights in rear (this includes liscense plate)

 

Also there is a connector around inside framerail at drivers rear tire. This feeds the orange, the blue, the brown, and i think the black from reverse switch. You can unhook this and test continuity from connector to lenses and from cab connector at booster back to this connector.

I had a similar issue a year or so ago. Mine ended up being broken ground wires in a perfect looking case.

maybe something in this thread can help too

 

Don't you have that reversed?

I thought green/orange is left side, orange/light-blue is right side - at least that's what the diagram shows, I just seem to remember green and orange on the left on my own truck...

 

Yes Chris, good call i had them backwards. Fixed, thanks!

 

You haven't got it yet.

Circuit 1. The brown wire. This goes to the running/taillights and the license plate lights. One brown wire goes back, has several splices in it where it goes to the left and right sides and the license plate lights. After it goes through the lights, it returns to the battery by the metal frame ground(black wire). The brown wire goes to the dim side of the dual filament taillights.

Circuit 2. Left turn/brake. This wire goes to the left rear taillight, goes to the brighter filament in the bulb, and is a lightgreen/orange wire. It returns on the ground also(black wire).

Circuit 3 Right turn/brake. This wire goes to the right rear taillight, goes to the brighter filament in the bulb, and is a orange/lightblue wire. It returns on the ground(black wire).

Circuit 4. Back-up lights. This wire goes back to a splice where it splits and goes to each side to each back-up lamp. It's a pink/black wire. It uses ground also.