A Few Questions

[Heavy Duty]

Hello again, I have a few questions about my 76’ GMC K25. Firstly my hazard lights do not work (they didn't work when I bought it) unless I press the brake pedal, then they light up but do not flash. The turn signals work just fine but not the hazards. What do you guys think it could be? My second question is about the gauge cluster. I am planning on swapping out the standard one for one with a factory tach, what all do I need to do to make it work? I am new to these old trucks so thanks for any help.

The poor ol’ k25 was stuck out in the snow this winter...

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[CSFJ]

did the hazards run a separate flasher relay in '76 like the later trucks?

 

[1987 GMC Jimmy]

I’m 99% sure that they did have both flashers, and the hazard one will be on the top of the fuse box where the turn signal one will be on the bottom conventionally. I would run with that first. Both of the signal indicators are supposed to light up when you press the brakes and the switch is pulled. I guess GM thought your brake lights were more important than the hazards so they overrode them when you did that. For the factory tach (not the aftermarket one with the integrated fuel gauge), you’ll need a new printed circuit specifically for tach clusters and possibly a slight repin of your cluster connector. I don’t know what that would look like if you do in fact need it, but I’ll tag someone. I know the aftermarket one from GM Sport or whatever that company’s called that I mentioned doesn’t require any modification, but you lose your 4x4 indicator and another one that I can’t remember at the moment. “Fasten Belts,” perhaps? Personally, I would go the route you seek to go on this. Are you planning to switch to the baby fuel gauge where the clock or the delete would normally go on the bottom left? @chengny

 

[CSFJ]

If it does have a flasher relay for each, swap the blinker relay into the flasher spot to check.

 

[Heavy Duty]

It looks to me like I am missing my hazard relay......

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I feel like an idiot.

 

[CSFJ]

lol. Now you know the first rule of electrical; check the fuse block first.

 

[Heavy Duty]

I’m 99% sure that they did have both flashers, and the hazard one will be on the top of the fuse box where the turn signal one will be on the bottom conventionally. I would run with that first. Both of the signal indicators are supposed to light up when you press the brakes and the switch is pulled. I guess GM thought your brake lights were more important than the hazards so they overrode them when you did that. For the factory tach (not the aftermarket one with the integrated fuel gauge), you’ll need a new printed circuit specifically for tach clusters and possibly a slight repin of your cluster connector. I don’t know what that would look like if you do in fact need it, but I’ll tag someone. I know the aftermarket one from GM Sport or whatever that company’s called that I mentioned doesn’t require any modification, but you lose your 4x4 indicator and another one that I can’t remember at the moment. “Fasten Belts,” perhaps? Personally, I would go the route you seek to go on this. Are you planning to switch to the baby fuel gauge where the clock or the delete would normally go on the bottom left? @chengny

My truck is full time 4x4 so the 4x4 light doesn't matter, the seatbelt light doesn't really either. I would like to find one with a clock, but as long as it has a tach I dont care to much.

 

[Heavy Duty]

lol. Now you know the first rule of electrical; check the fuse block first.

yup, live and learn I guess.

 

[1987 GMC Jimmy]

Well, in that case, I’ll attach the link for the aftermarket one. Pretty much plug and play for that one. It’s $215, though, but I don’t know where you’d be after the other setup. I would guess more or about the same, depending on what kind of deals you got on your parts, but I’ve never tackled it myself.

http://www.gmsports.com/content/new-tachometer-1973-1988-chevy-and-gmc-trucks

 

[chengny]

lol. Now you know the first rule of electrical; check the fuse block first.

And the second rule - which is a corollary to the first - is: When checking a fuse, don't go by the visual indicator - use a meter. Especially with AGC type fuses. The fusible material can be burnt or broken at the very end and be hidden by the metal caps.

 

[Honky Kong jr]

Pull the fuse and put your meter on it. In VW/Audi training we’d be in teams. I kinda gained a reputation. We’d bug cars and switch cars. I’d take blade fuses and snip the load side blade off. **** wouldn’t work but the fuse checked out until you pulled it and looked at it. I would also run a pin threw the Can Bus wires that screwed with everything.

 

[Heavy Duty]

Thanks for the help guys. 1987 GMC jimmy, thanks for the link, looks like I have a few options to choose from.

 

[75gmck25]

You can also swap in a tach cluster from a similar year, but they are hard to find. I believe you can swap in any cluster from 76-79 on your '76, but I'm not positive.

The tach uses three separate wires, so it does not require a different cluster printed circuit (floppy plastic sheet on the back of the cluster). I assume that is why gmsports can convert the fuel gauge to a fuel/tach combo.

I managed to find a '74 Sub tach cluster and swapped it into my '75. I could only use the early 73-75 clusters, since I have a mechanical oil pressure gauge.

Bruce