So I got a new turn signal switch after 2 years of using hand signals. I have everything working but the hazards don't flash with the key on. I still have power to the switch, fuse and flasher but they don't flash. Turn the key off and they work. Is this normal? This truck has had a lot of backyard repairs to the harnesses, including an ammeter bypass, and I've been cleaning it up as I go but I don't want to go searching for something that is supposed to be that way. Any help would be appreciated. I have a FSM for a 77 model year but it's not here at the house. Right now I'm pretty happy to have turn signals AND brake lights.

Um. I will check my '79 and see if it's the same.

Thanks Larry!

The only way turning on the key should effect this is if the turn signal for either side is on. Power for the 4 way is battery power and should be present at the flasher all the time, key off or on, power goes from the flasher to the switch, trace that wire and conform. There is a function internal in the switch, with key on, that if 4 ways are on and you turn your switch to left or right signal, the 4 ways are by-passed and that signal should flash. I have found a couple times where the switch is not doing this correctly and is cancelling the 4 ways with key on even though neither turn signal is active.
With key on, turn signal lever in center of off position, turn on 4 ways and just wiggle turn lever, sometimes this will make the 4 ways work, if so the switch is not fully centered all the time not allowing them to work proper. if this is the case,loosen the 3 screw's holding the switch and wiggle it around, re-tighten and see if this fixed it, if not, live with it or replace switch again.

The switch is not bolted into the column yet, I'm still playing with it. I still have power to the hazard switch with the key on but nothing out. Turn the key off I get power out. I squeeze it, wiggle it, nothing changes. Doesn't make sense. I'll pull the T/S fuse and see if it changes.

Did you check both sides of the flasher? Something might be putting 12V on each side with the key on, which would not let the flasher work.

Pull both flashers. Verify 12 volt battery hot at the 4 way flasher input and keyed 12 volts at the turn signal flasher input.

You got a faulty switch !

I thought about that but no.

I checked that also before I posted. But now here is the strange part. With the truck running they will flash but it's really slow. I cleaned the body grounds but that didn't change anything. These harnesses have been so hacked up that I don't know what is going on. The front park lamps are on when the key is on but they don't come on with the switch key off.

Probably among other things. When I pull or push the flasher switch they flash one time with the key on.

At this point I'm not worried, I have turn signals and brake lights and I can get the hazards to work if need be. It's all temporary anyway until I can get all the 93 dash, column and harnesses in.
Thanks to all for the help.

Have you tried swapping the flashers to see what happens?

Yes, I went and bought two new ones as only one of the originals worked.

The park lights should not be fed off the key. You have something very wrong. That is a simple system. Be careful on using the 77 fsm as there are differences between the 74 and 77 trucks. What does the fuse box look like? Maybe burned and melted. Or wired wrong.

The fuse block looks fine, I have not pulled it out yet though. I know someone wired the park lamps to the key to get daytime running lights on the aftermarket headlamps. I just don't know where they did it yet but that's the least of my concerns right now. I don't think that it is part of the problem though as the hazard/turn signal circuit is separate. The 77 manual is as close as I can get right now.

i wonder how much resistance you have across the terminals at the bulkhead where the alt feeds into the cab. that usually feeds everything in the cab, you mention the ammeter bypass, is the bulkhead ok?

I did finally get home and check my '79. Flashes with key off, continues flashing when I turn key on, stops flash when brakes applied. My ammeter is bypassed.

I looked at that too and cleaned it with contact cleaner but I don't have an ohm meter here at the house. It looked ok.

Thanks Larry, my 92 is the same way.

So I drove the truck a little the day I replaced the switch and repaired the dome light as well. Today I take it to the store and the hazards are working correctly key on and engine running also. I didn't do anything to repair this, it's just all working now.