instrument cluster swap

[Sprinkler-Man]

My truck 80 GMC K1500 donor truck 79 Chevy 1500.
The donor truck came with a factory tach setup that I would like to use in mine but my truck did not come with a tach.  What is involved in getting it to work?

[LTZ C20]

Well it's going to be fairly easy. There will be some small electrical work required but shouldn't be to hard. First off lets get some stuff figured out. Your truck has what gauges? Top left: voltmeter, top right: oil pressure, bottom right: coolant temp, bottom left: no gauge or a clock, middle left: speedometer, middle right: fuel level? Is this all correct?

Now I'm guessing with a tach the donor truck has the same setup. Except that the fuel gauge is moved down to the bottom left where the empty slot/clock is and the tach is now next to the speedometer. Correct?

Being that both trucks are late 70's, you should have an HEI distributor in your engine right?

[bake74]

     This Thread  clearly states that a 78 - 80 would work, earlier has a different oil gauge.
     This Thread  is really helpful, pay attention to the last comment by CaptKoas, "IF you get the whole cluster from a 78-up for your 80 it will technically plug in.  Verify the wires though."   I also believe you need the printed circuit board to swap also as pointed out by Capt. in the same article toward the top of the same page.

     Here are 2 pics showing 2 different places to put tach's.  The big RPM gauge that is on the right of the speedometer, they actually sell an aftermarket one that has a fuel gauge built into it if you wanted to add a clock to the bottom left corner where the small gas gauge is in this picture.
     ( the pics are from the second thread by the way)

[LTZ C20]

Bake74. Your "Thread" in green is a link I'm guessing and it doesn't appear to be working. I tried clicking on it multiple times, unsuccessfully.

[Captkaos]

His links worked for me.

Chris Lucas
73-87chevytrucks.com
captkaoscustoms.com
squarebody.biz

[bake74]

Bake74. Your "Thread" in green is a link I'm guessing and it doesn't appear to be working. I tried clicking on it multiple times, unsuccessfully.

 
     I just checked again and they are working for me also, I am no computer expert to tell you what to try and make it work on yours, sorry.

[Sprinkler-Man]

Well it's going to be fairly easy. There will be some small electrical work required but shouldn't be to hard. First off lets get some stuff figured out. Your truck has what gauges? Top left: voltmeter, top right: oil pressure, bottom right: coolant temp, bottom left: no gauge or a clock, middle left: speedometer, middle right: fuel level? Is this all correct?
yes..thats correct

Now I'm guessing with a tach the donor truck has the same setup. Except that the fuel gauge is moved down to the bottom left where the empty slot/clock is and the tach is now next to the speedometer. Correct?
yes...correct

Being that both trucks are late 70's, you should have an HEI distributor in your engine right?
yes

I have the entire cluster but someone has told me that i may need the original connector also.

[LTZ C20]

Good. Now I would follow the link that Bake74 provided. Like he said you will need the printed circuit board, the reason being most of the circuits are the same, however they differ slightly because of the added tach and relocated fuel gauge. Also double check all your wires.

Now for the wiring. Because you don't have a factory tach you will need signal from the distributor. On the side of the cap were the plug is and the battery wire. There is an unused plug, it is labeled "tach" simply put a female spade connector on a wire and plug it into that empty slot. Now run that wire away from the engine and through the firewall. Under the dash, run the wire to the tach signal wire in the new plug for the new cluster. That will provide signal to the tach to show rpms.

[Sprinkler-Man]

why would i need a circuit board if i am going to swap the entire cluster?  The new one already has a circuit board.

[bake74]

why would i need a circuit board if i am going to swap the entire cluster?  The new one already has a circuit board.

     The printed circuit board is usually considered a separate part, but if you are getting it with the new cluster you do not have to worry.

[LTZ C20]

Ditto on Bake. Only because it is removable and can be bought separately.

Now. Bake or someone could check me on this. The plug that goes into the printed circ board in Sprinkler Mans Chevy is set up for no tach. The GMC donor is tach. So, to make the signal for the gas gauge work properly, couldn't he remove the terminals for the gas gauge  and reinstall them back in the plug were the new printed circuit would have gas gauge signal leading to the small gauge quad? Also, couldn't he just pull the connectors out of the donor plug for the tach and insert them into the now empty spaces on the original Chevy plug and just run the wires to his new wires for the tach signal, power ground and distributor signal?

This means he wouldn't really need the new plug, he just swaps some terminals around and puts in a few in the empty spaces. The plug already had empty spaces because it had no clock or 4th small gauge. So in easy words, move the fuel gauge wires of the plug to the empty slots for small gauges and put in new wires in plug for signal to tach.

Does this all make sense??? LOL Sprinkler Man, are you confused yet? 😜

[bake74]

     I have not done this swap yet, I plan on doing it and read a lot about it, but from the 2nd thread in my first post, CaptKoas said it is just a plug into new board and go, so taking him at his word (I know he has done it a couple of times), you should just need to plug it in and go.
     Sprinkler-Man, please keep up updated on how and what you had to do to make it work.

[KWKENUF]

Yes LTZ C20,  you are correct in your statements about not needing a new plug.  To change from a non-tach cluster to a tach cluster,  you DO need to re-pin the plug,  even if the clusters are from the same year.  Printed circuits are different between the cluster types also.  Get an electrical schematic from both years and cross-reference all the wires you are dealing with.  The printed circuit from the 79 "should" work with the 80,  as long as you understand and get the wiring correct for the components you are dealing with.

[LTZ C20]

Ok sweet. That's what I thought.

There ya go Sprinkler Man, that should be everything you need. Just gotta re-pin the old plug.

[Sprinkler-Man]

Wow...my head is spinning.  It almost seems like it would be easier to put a after market tach where the clock would be.  I really was hoping it would be more of a plug and play swap.  I will keep you all posted on my progress.