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1973 Chevy 3/4 chasing electrical bugs

7

73chevy3/4

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Vail, AZ.
Hey everyone. I'm have an issue with my truck and wondering if I could some advise with.

I just got the truck to start running right due to carb getting hot and was boiling fuel.

Two days ago the running lights, brake lights, dash lights and flashers stopped working in the truck. What's confusing is that the blinkers still work.

I thought it might be the headlight switch so I replaced... Didn't change
I replaced all fuses that i could find, and none where blown... Didn't change

Both front and rear running lights don't work so I would think the issue is under dash...

Any advice would help....
 
Ok, might have to think about this one for a little while. In the meantime, we need to clear up some terminology.
You say the flashers don't work, but the blinkers do.

Which is which?
Are the blinkers the turn signals and the flashers the emergency flashers? I figure that is so, but want to make sure.

The brake lights use the same bulbs and wires as the turn signals, so its puzzling that one would work without the other.

Sounds like a main wire connector may be loose somewhere, but I will have to check my schematics to see if I can work it out.
 
Well, the good news is, I may have found your problem. Bad news is, I have no idea what the heck I am looking at.
Worse news is, I'm betting I can't show it to you.

I have got a ton of stuff going on right now, had just a couple of seconds and checked my schematic.
Saw a connector that looks like most every thing goes through, although I may be wrong.
I am having to write this between phone calls and arguments with other folks about some equipment that is down.
I will post the picture, but I don't think you can see it unless you are a member. Don't know for sure.

If I get another minute, I may try to e-mail it to you, or maybe somebody else can post it in a way you can see.

The connector is that triangle shaped connector just to the right of center. it may be the turn signal switch, not sure until I get a chance to study it more.

73-76_cab_inter.jpg
 
yes, the turn signals work, and the emergency flashers don't.

I just took apart the main fuse block and checked the connections there everything looks good no corrosion there. everything tighten back up and still nothing.

I can't see the picture...
 
Do you really think its the turn signal switch? I was thinking maybe brake light switch, due to the fact the the turn signals are still operating.
 
There should be two canisters, one for turn signals and one for hazards.

If you're missing one canister, that would 'splain it right there. I can post a pic of the fusebox with the locations of 'em if required.

Otherwise, if you have two canisters, swap them. If the turns then fail and the hazards work, get a new canister. If the problem doesn't follow the canister, then you're off to check wiring, etc.

-- A
 
its not just the flashers and turn signals...

its also the dash lights and brake lights that are not working...
 
Ugh. You're in for some fun.

Your BEST bet will be the real factory electrical manual, either $$ from Helm @ http://www.helminc.com/ or lots cheaper on Ebay.

However, to get you started I have some non-year-specific stuff on my Brochures site (link below). Pick "Wiring" under "Technical Info".

-- A
 
ok i swapped the cans out... yes the emergency can is bad...

but if the turn signal and brake light use the same wires why would u think its wiring?

would you think its a switch?

wouldn't wiring cause the fuse to blow? haven't blown any fuses yet...

this one has got me stumped on where to start looking...

there is no running lights either, both front and rear...
 
if i forgot to mention that all lights and signal where working prior to this... no fuses had been blown either.
 
A shorted wire will make a fuse pop, sure. An *open* one, i.e. one that's disconnected, won't. It just won't work.

Could be a loose or corroded connection anywhere along the line, and the turns and marker lights are annoyingly interconnected, including the negative side being switched some places.

-- A
 
what gets me is that the turns signals, and headlights are working, but nothing else is working...

what would cause the dash lights to go out?

where should i start looking first?

i live in az there's not much corrosion on any wires and connections. there is a lot of dust but not much else.. lol
 
Could be a broken common ground, retrace your steps from working on the truck and look for broken grounds around engine compt.
 
ok, I just replaced the brake light switch and still no luck, so it probably a bad ground, but would it be in the cab or outside of the cab? through the fire wall it looks like the light circuit is split in two, so could it before the circuit splits?
 
This seems to be a strange problem. Most of the parts have little in common. The thing I was looking at was the turn signal switch.
Use a meter or test light to make sure that one side of the brake light switch is hot, and if it is, then its probably going to be your turn signal switch or the hook up to it.

This is a pretty old truck. You might suspect bad bulbs in a lot of the problems. These things will sneak up on you.

I just had the exact same thing happen to me. I have two cars that are pretty much identical.
One of them had a problem with the brake light switch which let the brake lights work, but not the antilock or cruise control.

I replaced it and all was well. Then, two weeks ago, I was driving the other one and a guy told me I had no brake lights at all.
So, I ordered a new brake light switch for that car.

Didn't fix it.
Turned out, both brake lights were burned out. Probably one had been burned out for a long time, but no one mentioned it.
When the other one did, a guy was motivated to tell me when he almost hit me.

The dash lights on that truck are dim on its best day, if the bulbs have been burning out, maybe the last one went.
And maybe even some of the exterior bulbs.

Otherwise, there are several connections that might be bad to kill parts of what you have.
My schematic shows that they are there, but where they are.

Try holding the brake down while wiggling the turn signal switch if you have power to the brake light switch and the flasher switch.
 
That still don't make sense. All of the bulbs going bad all at once, remember the bulbs still light up when the turn signals are on. All the light in the interior were working also. but what I don't get is that the rear and front come out of the fuse block in two different circuits, and they are both not working. I replaced the headlight switch and brake switch, and still nothing... its got to be either the turn signal switch or a bad ground in the cab. But the turn signals work, so i'm guessing it a bad ground in the cab... just can't seem to find were that circuit is all grounded at.
 
Im no expert, but your common theme is everything thats out does not run thru the key switch. They all will operate with the key off. There is a main power wire that runs from the fire wall into the cab. I cant remember if it was a fusable link that far back or not, but Id look around and make sure you have power there as well.
 
I would look and see if its had a trailer hitch installed ,many times the wiring under the truck gets hacked when someone puts one on,or the harness plugs that were factory installed corrode and cause intermittent troubles...but that wont affect the dash lights...................................................................I would check ALL the fuses,sometimes one not marked for the curcuit thats giving grief powers some part of the curcuit..see if all the fuses have 12V at both ends with the key on...sometimes the old glass fuse boxes got wet and corroded between the two halves where they bolt together too,that might be a possible cause.................................................................................if the "instrument panel and gauges" fuse is good and there is power there at both sides of the fuse,perhaps a ground wire that grounds the dash near the E-brake release has come off,or the printed curcuit board may have failed. (pretty rare though)...the rehostat built into the headlamp switch also dims the dash lights,many get corroded and may not let them come on at all...
 
Ok, so everyone knows... I took it to my local guy that knows more about the electrical side of this truck than me. He found some corrosion behind the fuseblock and we were about to get them working... Thanks for all the suggestion.

Time to put out the cash and rewire the truck. He said the PO had really hacked up the wires in the cab.
 
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