Trying to chase down an issue with the hazard lights on my 78 F250. When I put the hazard flashers on with the truck on and in park, nothing happens. But if I put my foot on the brake pedal, my two turn signal arrows on the dash light up and stay on until I take my foot off the brake (no flashing though). I replaced the turn signal switch, the hazard flasher plug thing behind the dash, and the brake light switch on the pedal. Anyone have any ideas as to what could be going on?

 

You put a new hazard flasher in place? It is separate from the signal flasher you know.

 

Yup. They look exactly the same, so I unplugged one and tried the turn signals. Turn signals stopped working after I did that, so I knew the other flasher was for the hazards. That's the one I replaced, but still no working hazards.

 

with the hazards off, do both rear brake lights work normally when the brake pedal is depressed?

 

Just checked, and yes--with the hazards off, the brake lights do work normally. Here are the brake/hazard combos I've tested and the outcome:

1. Brake pedal depressed, hazards switch off: Brake lights on, no dash lights (works as it should)
2. Brake pedal depressed, hazard switch on: Brake lights on, no flashing, turn signal arrows on dash illuminated but not flashing, headlight hazard lights are on but not flashing. As soon as I take my foot off the brake, all headlights and taillights turn off.
3. Brake pedal NOT depressed, hazard switch on: Brake lights off, no lights on dash, all headlights and taillights are off.
4. Brake pedal NOT depressed, hazard switch off: Brake lights off, no lights on dash.

So basically, there's no signs of my hazard lights working until I put my foot on the brake, which causes both turn signal arrows on the dash to illuminate but not flash.

 

 

That's awesome--thanks!

 

As I was going through the testing protocol in those documents, I realized my fusebox is different from all the 1978 f250 fuseboxes references I can find. The previous owner of my truck swapped in a 460. I wonder if they used the wiring harness/fusebox from the donor vehicle. If so, I wonder if there some wrong wiring given the weird occurrence when I put my flashers on and step on the brake.

 

73 to early 77 has got the smaller fuse box, that looks like a standard late year 77 to 79 fuse box. No need to swap in a different fuse box for a 460 engine swap. I have some electric diagrams in the (Ford Truck and then some) info thread up in this red stickies.

 

Have you ever just reached in and turned the flashers on ... then walk around the truck checking all 4 flashers? Do they in fact flash?

Fusebox in post # 8 above looks normal to me.

 

Yea I should've included that in the third one. It should read:

Brake pedal NOT depressed, hazard switch on: Brake lights off, no lights on dash, all headlights and taillights off.

But, I just noticed something else weird. When I have the hazard switch on and the brake pedal depressed, the flasher lights illuminate on the front of the vehicle, but don't flash. As soon as I take my foot off the brake, they turn off. The rear brake lights are the same. hazard switch on and foot on brake...the brake lights light up. As soon as I take my foot off the brake, they turn off.

I'll edit the post you quoted tbear853, to reflect these.

 

All brake light, turn signal light, hazard flasher light power is coordinated there on the steering column.

• A turn signal will take precedence over a brake light, which is why you can signal a turn with the brakes on.
• A brake signal will take precedence over hazard flashers, which means if you step on the brake pedal while flashers are on, the flashers go solid ... all 4 corners.

It is intended that hazard lights be used only when a vehicle is stationary and a hazard to other drivers, and brake lights are of more value to other drivers when they only come on and stay on solid so others know intent.

I walked out to check my memory after posting last, and yes ... when my hazard flashers are on and I press the brake, the 4 hazards stop flashing and all 4 go solid ... as do the green arrows. I've rarely looked at it like that, but I do recall police cars doing it the exact same way back in the days before we had bar lights when I often used the hazards with my bubble on the shoulder of a highway. This today test is likely one of maybe three or five times I've tried it on my '77 since 1986.

 

Interesting! So that makes me think this green highlighted path is working as it should. Basically when I put my foot on the brake with the hazards switch engaged I get power to my brake lights and front lights, and guessing the way it's wired makes it so the flasher doesn't flash. That leads me to believe there's something going on with this other path--the Red/White wire (#383). Not sure how to check that. Maybe I'll check the fuses first to see if any of those are blown. If not, then maybe I need to replace some wires between the fuse box and the flasher.

 

Did the flashers them selves work? Might need a mirror or other reflective surface in dark unless you get a helper. The green indicators nor hazard flashers should flash with the brake applied, but the arrows should light up with the hazard flashers ... steady on when the brake is applied..

 

Like in the other thread, is that a missing flasher there? Was it missing when you were testing?