TACH ON DIESEL MODEL TRUCK

[echo7bravo]

I am swapping the cab from a 1979 diesel truck onto the chassis of my 1986 K10. The new cab (from the diesel truck) has a tachometer in the instrument cluster. My question is regarding the cab wiring. Does anyone know what wire leads to the plug on the back of the tach?

I'm feeling froggy but not quite enough to try and trace the wire backwards.

 

[Honky Kong jr]

im Not sure on these trucks, but most diesel stuff I’ve played with the tach is driven by the alternator.

 

[echo7bravo]

That's what I thought too. But my truck has that GM performance crate 350 with a MSD HEI distributor. I was thinking that there were COIL, GND, and 12v connections on back of the tach and that my HEI had a tach terminal on it. I could be totally wrong.

Was hoping that I could just find the right wire to connect up to my gasoline engine.

 

[Honky Kong jr]

@bucket or @HotRodPC would probably be able to answer better. Me I’d just use a gas tach cluster and sell the Diesel cluster

 

[Frankenchevy]

how high does the diesel tach go anyway? can't be much more than 3-4k unless they were really optimistic.

 

[bucket]

That's what I thought too. But my truck has that GM performance crate 350 with a MSD HEI distributor. I was thinking that there were COIL, GND, and 12v connections on back of the tach and that my HEI had a tach terminal on it. I could be totally wrong.

Was hoping that I could just find the right wire to connect up to my gasoline engine.

You are correct. Ign 12v, ground, and tach signal. Tach signal goes right to the hei cap, it's the spade right next to the big ign spade.

@bucket or @HotRodPC would probably be able to answer better. Me I’d just use a gas tach cluster and sell the Diesel cluster

I think they are the same.

how high does the diesel tach go anyway? can't be much more than 3-4k unless they were really optimistic.

Interested to know this as well. Iirc, my '77 gas tach only reads to 5K.

 

[echo7bravo]

how high does the diesel tach go anyway? can't be much more than 3-4k unless they were really optimistic.

It is a 5000 rpm tach. I thought the tach were all the same just where they hooked into the ignition system.

What I am trying to figure out is where the tach wire travels to once it leaves the tach and enters the wiring harness. What color wire and where it is located when it enters the engine compartment. That way I can tie it into the tach signal spade on the HEI cap.

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[Frankenchevy]

this is what I'm going with for all my gauges...sorry probably not helpful, lol

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[bucket]

The tach harness was it's own stand alone harness. The signal wire just passed through a grommet in the firewall.

 

[echo7bravo]

The tach harness was it's own stand alone harness. The signal wire just passed through a grommet in the firewall.

You don't by any chance know the where and color do you?

Only reason I ask is it is one of the differences between my original cab and my donor cab. And I have no idea what all the POs have hacked off or "deleted" from the donor cab. I think I can pretty much figure out everything else since it should be the similar if not the same as far as blower motor, fuel tank, horn, headlights, etc.

 

[echo7bravo]

this is what I'm going with for all my gauges...sorry probably not helpful, lol

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Not at all. But if I ever find the need for an advertisement for tachometers I will let you know.

 

[crpntr78]

The wire coming off my tach is green.

 

[echo7bravo]

Got up and looked this morning. Tach signal is dark brown.

Pink to 12v and black to ground. Found where the tach wire comes through the firewall. Hopefully all goes well with my install.

 

[highdesertrange]

well if it is a 1979 and it was a diesel that would be the 5.7 liter diesel. I was told the square body diesels never came with a tach. interesting. highdesertranger

 

[echo7bravo]

Heck it could have been added over past 39 years. I just know rpo codes and back of sun visor say diesel. And the diesel idiot lights above speedo. And that there is a tach and small fuel gauge. But it’s about to become a 1986 LOL