I have a 66 f 100 that has a emergency flasher. I notice the terminal at one of the switch powers up when brakes applied. But have no brake lights. Are one of the other terminals suppose to power up also? The four ways do work at least the fronts and the cluster lights. Can the switch be causing the inop brake lights?

 

The 4 way switch could cause no brake lights and the signal light switch also. I read where you say, stepping on the brake puts power to the 4 way switch. You say, fronts and clusters (green dash indicators) work. Are you saying the rear brake bulbs are NOT working, when 4 ways are on?? Do your tail lights illuminate brightly when parking lights are on and nothing else?? You've tested both rear, stop n tail bulbs out of their receptacles and both filaments work on each. Tests below are simple and a process of elimination.

A couple tests. 1 all lights off, emergency flasher off, signal light switch in center, not in a turn position. Remove the 2 wires from the brake light switch on the master cylinder. Jump the 2 wires together, a cotter pin works well or the shank of a nail with head cut off or what ever you can come up with. Go look see if brake lights are on, yes-no?? If No, turn the ignition key to the on, run position. Not sure on 66 but some trucks the ignition has to be on for brake lights to operate. Work with key On, yes-no??
Is your 4 way a red plastic push pull knob?? If yes does red knob illuminate?? If no, see if red knob unscrews from the switch, see if there is a bulb under knob, verify the bulb is good. Your 4 ways should have a flasher of their own, I'm assuming it's good as you say fronts and clusters flash. Just operating signal lights only, key on run position, left then right, do the rear signal lights work?? Just trying to verify that wiring and grounds are all good for now. Cap

 

Hi right" the rear bulbs dont light when 4 ways are on. The tail ights shine brite when i have the headlights on. All the turn signal lights are good, like I said when I apply brakes the red with blk stripe applies power to one of the terminals on the 4 way switch but dosnt seem to go any further then that. I was wondering if the switch may be bad. Its just funny that the it flashes like it should but no brake light. I did order a turn signal from Carpenter but haven't installed it yet. Haven't had chance to try what you suggested .

 

Although I have not found a schematic with 4 way hazards, the 810 red with black stripe is also the power into the signal light switch. With sig switch in center position the 810 wire feeds both wires to the stop bulbs. As 4 ways were an option, my 66 does not have. I would wait and put in the new signal light switch. Meanwhile if you choose, you can check the 810 wire at the sig light harness connector to be sure it is reaching the wire there when stepping on the brake. I've added the link, I hope, to the schematic I checked. I will continue to look for schematic with 4 way.

http://www.fordification.info/tech/images/wiring/66extlight2s.jpg

 

Hi Rich Update I repl

Hi Rich Update I replaced the 4 way switch with new OE switch but the same thing happens With brake applied terminal frt left terminal powers up. From what im hearing is the turn sig circuit is totally separate from 4 way circuit. There is 2 wire diagrams for each circuit in ford manual . My question is what is suppose to happen with power flow when brakes applied on 4 way equipped trucks. The power is getting to 4 way switch but then stops there. Update I replaced the 4 way switch with new OE switch but the same thing happens With brake applied terminal frt left terminal powers up. From what im hearing is the turn sig circuit is totally separate from 4 way circuit. There is 2 wire diagrams for each circuit in ford manual . My question is what is suppose to happen with power flow when brakes applied on 4 way equipped trucks. The power is getting to 4 way switch but then stops there.

 

There were some 4 way/ hazard systems that would stop working when brakes applied and might even keep the front signal bulbs on steady. Not sure it that applies to our 66's as mine has no 4 ways.

I had asked you back a bit if you have the in dash switch with matching push pull knob like the rest of controls or the red plastic knob with a bulb under the knob. Maybe someone reading this thread that has a 66 with 4 ways working properly could add how they work when brakes applied.

DID YOU get and install the new signal light switch yet?? I think that is where your problem is.

As mention, the same red black wire powering your 4 way switch ALSO powers the brake lights THRU the signal light switch when brakes applied. That is why I asked you to find the red black wire at the signal switch connector and with a test light or DVOM see if the 'wire has power when brakes applied. If yes then, the two wires, Yellow/Black 283 and Green 282, that go to the brake lights should also have power. If they DO NOT, then there is a failure in the signal light switch. Sig switch has to be in the off position. The schematic shows those two wires, the Yellow/Black and Green May be in a separate connector of their own.

Want to mention this. Not knowing the history of the truck, see if you can verify that wire colors match to each other each side of the connector. Also when you go to change the signal light switch, the connector body may be difficult or not fit thru the hole in the column, which means you might have to remove the wires from the connector and reinsert them after feeding the wires thru the opening. I know that is kinda dumb, but remember trying to remove switch from my parts truck and it still sits out back with the switch half out. Cap

 

This link delves into your problem some. Although the OP just needs info to hook into an aftermarket wiring harness he is installing. There is much, much reference to original wiring and parts with pictures from the responders about the Ford installed 4 way system. It might help answer your questions. Please keep us up on your progress. Cap

https://www.ford-trucks.com/forums/1590581-hazard-switch-wiring.html

 

Update I replaced the 4 way switch with new OE switch but the same thing happens With brake applied terminal frt left terminal powers up. From what im hearing is the turn sig circuit is totally separate from 4 way circuit. There is 2 wire diagrams for each circuit in ford manual . My question is what is suppose to happen with power flow when brakes applied on 4 way equipped trucks. The power is getting to 4 way switch but then stops there.

I have an update of my brake light issues. I replaced the emergency light and turn signal switch. Although i bought the turn sig switch from Dennis carpenter I found that the wires were not the same wire colors as the wire diagram. I used the old switch to plan the correct way to wire it. Eventually I found the correct way and perm spliced all connections. Thank you to the replys .

 

fs1957, Assuming all working correctly now. Hope so that would be great. You're welcome on the replies. Helping out with problems is good for knocking the dust of these old brains.
Enjoy your Truck, Cap