hey all/ i have a 1986 F250 4x4 with a 6.9l. my brakes and hazards have never worked (previous owners work) but all the other exterior lights work just fine. i don't seem to be getting power going to the hazards and i intermittently get power to the stop feed wire going to the brake light switch. I installed a new turn signal switch and used the OEM test procedure to ensure it functions properly, what does seem to be strange, i have no power at fuse #1 which is stop/hazards. i looked at the back of the fuse block and there is 1 solid red wire and 1 sold yellow wire on fuse #1, looks like 16 ga or something, Neither of those wires have power and they just go up into the factory harness ( ill need to full take the harness out to see where it goes). i tested the hazard flasher wires and there's no power.

i hooked up a 12V source to the brake light switch so it would feed the brake circuit 12V still no reaction from the rear tail lights. im running out of ideas. any help would be greatly appreciated.

 

Being the fuse for both dose not have power i would pull the fuse put power to the brake light switch so it back feeds to the fuse so you know what side of the fuse is the output side.

So I am thinking if you put power to the other side and install fuse they should work if everything else is fine.
Then you could look into why it gets no power.
Dose everything else work?
Dave. ----

 

Rule #1 when troubleshooting lighting; Use a testlight or if you are using a voltmeter, make sure everything stays plugged in when testing.

You can see in the diagram below, both the brake and hazard circuits are fed from the same fuse on the upper right side of the diagram, fuse #1 like you mentioned in your post. That fuse is hot all the time. Another fuse that is hot all the time is for the domelights, fuse #8 and the marker lights, fuse #4. You have power to these? They have two main parts of the fuse box or what they call "busses". One buss from the keyswitch that feeds the fuses that are hot in run, and another buss that feeds all the fuses that are hot all the time.

 

Forget what I said above, after looking at the diagrams a little more closely, I was wrong. Fuse #1 is not fed from the buss in the fuse box, it has it's own feed wire from a splice in the power distribution yellow wires. You can see it in the diagram below.

 

I suspect fuse link M. See pages 20-21 here:

Charge & Power Distribution - Diesel Engines - Gary's Garagemahal (the Bullnose bible)

The yellow wire at fuse #1 should have battery power at all times. Follow that wire upstream and you will see fuse link M. If that fuse link were to open, nothing else would be affected except fuse #1 on diesel models. (Gas models are wired differently, and that same fuse link feeds a LOT of other items.)

You can see the location of fuse link M here, page 20, figure 1:

Charge & Power Distribution - Gasoline Engines - Gary's Garagemahal (the Bullnose bible)



Hmm, not sure what's going on. Could be a separate problem, or it could be what caused fuse link M to open. Wiring diagrams are here:

Turn, Stop, & Hazard Lamps - Gary's Garagemahal (the Bullnose bible)

I'd suggest disconnecting the plug from the brake pedal switch. On the upstream side is wire #10, light green w/ red hash marks. It is supposed to always have battery power available from fuse #1, presently dead. On the downstream side is wire #511, plain light green w/ no other marks. If you applied battery power to wire #511, and the turn signals are off, the brake lights should illuminate. If that's what you did, I'm not sure why they didn't work. Try removing both rear turn/stop lamps, and check for continuity to ground at wire #511. With both bulbs out, there should be no continuity. If there is, you've got a wiring problem to isolate.

You may find details here to be helpful when troubleshooting:

https://www.ford-trucks.com/forums/1...ing-guide.html

 

The circuit you want to test is the yellow 37 circuit. Shown in the diagram below, it's fed by fusible link W.

 

Ooh, I missed this in my first read. The brake light switch is a funky design that moves with the pedal, and flexes the vehicle wiring each time you apply the brakes. No idea why Ford did this, as opposed to a fixed switch. Carefully check the wires adjacent to the switch. This is a common spot for breakage due to the poor design.

 

What does this sensation feel like? I've heard of it, but have never experienced it.



BTW, none of your pics are coming through, at least on my computer or phone. Not sure what's going on, but today I was prompted to complete an anti-bot capcha before I could even log in. This forum must be the next target of Reddit raiders.

 

The picture below does not show the location of fusible link W, but from the diagram above you can see it's connected to the same place that fusible links R,J,U. The picture below does show those fusible links.

 

I will try links instead. This link shows fuse #1 fed by a separate yellow wire from circuit 37. http://www.garysgaragemahal.com/uplo...85485_orig.jpg

This link shows where the circuit 37 comes from, it's the very top yellow 37 wire and leads to fusible link W http://www.garysgaragemahal.com/uplo...24562_orig.jpg

This link shows the actual picture over by the starter solenoid. They do not have fusible link W shown, Ford's diagrams are full of typos. But it should be over there in that mess of wires in this link. http://www.garysgaragemahal.com/uplo...62877_orig.jpg

 

I got the anti bot yesterday on my pc and many today on my phone.
Between this now and how slow it can get i almost want to give up LOL
Dave. ----

 

One more thought:

What size fuse was installed at position #1? It's supposed to be 15 amps. I'm wondering if some still undetermined fault caused the fuse to repeatedly blow, such as a bulb shorted internally. The mouth-breathing previous owner (always blame the PO) got tired of replacing fuses, so instead of finding and fixing the problem, he went to a bigger fuse. This may have been enough to now blow the fusible link instead, at which point he sold the truck thinking it had some horrible unrepairable problem.

 

Thanks for all the help everyone! that fusible link W was the issue, it was left off the starter solenoid. just hooked it up and everything was good to go!