76 GMC gauge cluster swap (no tach cluster to a tach cluster)

OldBlueDually

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I figured before I go making a LOT of work for myself, and possibly screwing something up I wanted to ask all of you first (see, I have learned my lesson the hard way in the past!!).


I am going to be putting into my truck (76 GMC Sierra Grande (1 ton)) the gauge cluster/instrument panel from my parts truck (76 GMC Sierra Classic 15 (1/2 ton)). In my truck the gauge cluster had the lower left small gauge area as a red indicator light “BRAKE”. The other small gauges were the typical volts/temp/oil pressure. The two big gauges were speedometer & fuel.


Now, in the parts truck, the lower left gauge is fuel, the others being volt, temp, oil pressure. The two big gauges are speedometer, and tachometer. The tach has its own wire harness, so that is easy to install.


My question is do I have to do anything, or change out wiring…etc. to make this gauge cluster work? The main cluster wire harness plug differences look like 1 wire color difference on one spot between the two plugs (my truck & parts truck), and there is a wire missing in my plug whereas the parts truck has a wire there. I forget which numbered spots, but I could look.


Has anyone dealt with the above, and if so what have you done?


Thanks everyone!!!
 

Big Chip

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It should plug right in and work because the printed circuit is set up for the fuel gauge location but if it doesn't let me know because I have a tach cluster that I was going to install some day.
 

OldBlueDually

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I certainly hope it is that easy! If I have to re-pin a wire or two I guess that is fine too, but I am hoping I don't have to.

Wanted to check before I accidentally make more work for myself :D
 

AuroraGirl

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I think the main wiring changes came after 81 I believe but that's a repin. A tech esp early diddnt use different wiring because twch had it's own. The printed circuit moved the fuel gauge in most instances but there is the rate small in tach fuel gauge
 

Bextreme04

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there are differences year to year, but since you are going from a gauge cluster to a tach/gauge cluster it should be plug and play. I would ring out the parts truck harness to see where power and grounds are located and make sure they are the same on your truck at least. Those are the ones that will let the magic blue smoke out.
 

squarelyfe

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Look at the printed strips compared to each other. You may find one had two empty spaces and another has 3. One may have to be re-pined
 

OldBlueDually

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Good news, now that I can fire up the truck, everything in the cluster works as it should! I need a new sending unit for the temp gauge however, it does not work. When we (my dad and I) grounded out the wire it pegged the gauge so we know the wire works.
 

Sepulvd

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Good news, now that I can fire up the truck, everything in the cluster works as it should! I need a new sending unit for the temp gauge however, it does not work. When we (my dad and I) grounded out the wire it pegged the gauge so we know the wire works.
So was just plug and play
 

75gmck25

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I can’t find my notes to verify, but IIRC the TS6 sending unit worked well with the ‘74 tach cluster I have in my ‘75 GMC. It has the right button connector and thread size, and Autozone had it in stock.
At normal operating temp with a 195 degree thermostat it shows a little more than 1/2 way between 1/4 and 1/2 scale, and will “spike” up to near 1/2 scale for just a minute or two just before the thermostat first opens up.

The correct early GM sending units have been discontinued, so getting a new one to work is not that easy. Most make the gauge read way too low.

I think your cluster still has an ammeter, which I converted to a voltmeter because the old ammeters seldom work correctly. I bought the gauge from LMC and then followed some simple directions I found on the internet to connect it to power and ground.
 
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OldBlueDually

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So was just plug and play

Yup, plug the wire in and go! However, not sure what the sending unit is from, so I may have put something different in than what should be there..??
 

75gmck25

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This is a picture of the gauges in my ‘75 GMC tach cluster where I used the TS6 sending unit for temperature. I also converted the cluster to a voltmeter.

I have the in-dash temp gauge and a separate mechanical gauge since I found it hard to match sending units without any numbers on the on the in-dash gauge .
 

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