Corrected title.... Original tachometer cluster in a 1991 K3500. Fuel gauge not working.

[Hershel W Cecil]

Good Morning Everyone,
I bought this 1991 K3500, 454 V-8 meshed with the 4L80e transmission. It is a tow truck and does not have the original bed on it.

The previous owner definitely knew how to cheat and short repairs in the sloppiest way imaginable. Here are a few things I found, just for laughs and then I'll post my question.

Wiring to the transmission were just twisted together and not protected from shorting out.
Fuel pump assembly was RTV'ed into place.
A fuel pump switch was installed on the dash, when the only thing wrong was the pump relay.
Exhaust was hacked into 6 pieces and left hanging. I think they did this to work on the transmission.
They didn't use butt connectors for any electrical repairs. My collection of wire nuts is building the more I work on it. lol
The fuel fill hose was ran in such a way that the neck was kinked to almost closed and rain could easily get into the tank.

OK, maybe you get the picture.

Now, I'm going thru and "tinkering" with this truck in my spare time and the latest focus is the fuel gauge.
With the RTV mess they left on the fuel tank and pump assembly, I just replaced both. Don't have the patience to try and clean it up.
The new sender is putting out proper ohms, got rid of the fuel pump switch on the dash and got that system working correctly, But the fuel gauge is now showing full grounded condition..

Ok, now, I haven't pulled the cluster out yet but doing some research, this gauge cluster is not from a 1991 truck, but rather a 1994 truck. With the other "repairs" I'm finding, I'm almost scared to look behind the cluster. lol

So, I've looked thru the Chilton and can't find the electrical schematic for the 1994 instrument cluster but do have it for the 1991 but I know the connector is different between the 2.

Simple question... Is the wire for the fuel gauge on the '94 purple like it is on the 1991?

I'm hoping I don't have another tweeker repair behind the cluster. lol
I'll be able to look at it this Sunday and just want to go in with some information I can't find in the Chilton.

I had a 92 and 93 GMC pickup and dash clusters were repeatedly replaced under warranty because on of the gages seemed to always be non working or erratic. So in my experience the clusters are frequently non working. There are a number of repair shops that will repair them if that's the issue.

 

[someotherguy]

88-94 the PRNDL is a simple mechanism operated by a cord that attaches around the shifter bowl of the column. Most common issue is the clip on the column has popped off or someone broke the cord while carelessly pulling the cluster out.

Richard

 

[DerekTheGreat]

Careful with the moonie cluster, it's not a plug and play swap unless you get one from a 1990.5 truck. You'll need to swap wires around in the harness to get it to work correctly. That and I think it'll take your tach signal wire and run it straight to ground, which will trash your coil. Personally, I'd just leave the stock cluster in it and deal with the fuel gauge another way until properly fixed. Tracking mileage is one of them.

 

[someotherguy]

Careful with the moonie cluster, it's not a plug and play swap unless you get one from a 1990.5 truck. You'll need to swap wires around in the harness to get it to work correctly. That and I think it'll take your tach signal wire and run it straight to ground, which will trash your coil. Personally, I'd just leave the stock cluster in it and deal with the fuel gauge another way until properly fixed. Tracking mileage is one of them.

I'll disagree with the 1990.5 statement and say 1991. In 1991 both style clusters were available - moonie and needle - and they do swap. You are 100% correct that 1988-1990 clusters do NOT swap with 1991, and of course vice-versa. There are 3 wires that need to be moved around in the connector to go either direction.

Furthermore, any cluster swap on a 1988-1991 truck will potentially involve needing to recalibrate the speedometer since the configuration is done right there on the cluster. That is, unless you just get lucky enough to score a cluster from a truck that had the same axle ratio and tire size that your truck came with. Buy a lotto ticket..

Richard

 

[DerekTheGreat]

Yeah, that's the right ticket. I forgot what the cut off is timeline wise. I haven't had to do one of these swaps in six or so years. Funny enough, I've done it twice and in both cases, the speedo calibration suited my application. I buy lotto tickets every time I get gas and still not able to retire. Oh well, it's better than wasting money on cigarettes.

 

[Dajain]

Careful with the moonie cluster, it's not a plug and play swap unless you get one from a 1990.5 truck. You'll need to swap wires around in the harness to get it to work correctly. That and I think it'll take your tach signal wire and run it straight to ground, which will trash your coil. Personally, I'd just leave the stock cluster in it and deal with the fuel gauge another way until properly fixed. Tracking mileage is one of them.

So, you're saying the Tach trucks had special wiring from the factory?

Sounds far fetched and odd from Chevy back in those days, That's something Ford would do,

 

[Dajain]

Yeah, that's the right ticket. I forgot what the cut off is timeline wise. I haven't had to do one of these swaps in six or so years. Funny enough, I've done it twice and in both cases, the speedo calibration suited my application. I buy lotto tickets every time I get gas and still not able to retire. Oh well, it's better than wasting money on cigarettes.

That made no sense whats so ever
Thanks for the input though

 

[Dajain]

I guess Ill update whether the moonies work for my truck. They are already ordered AFTER the expert advice chirped in,,,,,,

Never imagined Chevy would take Fords lead on this/SMDH

 

[89RCLB]

As @DerekTheGreat noted, unfortunately, you can't just plug that moonie cluster in. There are, in fact, three wires that would need to be moved around in the connector that the cluster plugs into. Moving the wires around is actually rather involved!

I've never tried it, but you might be able to take the fuel gage motor from the mooonie cluster and swap it to your tach cluster to test. Removing the needle is easily done with the tines of a kitchen fork. Getting the gage reading set correctly after swapping the motor would be the real challenge but not all that difficult.

 

[DerekTheGreat]

That made no sense whats so ever
Thanks for the input though

Read someotherguy's post (#24) and then reread mine (#25).

So, you're saying the Tach trucks had special wiring from the factory?

Sounds far fetched and odd from Chevy back in those days, That's something Ford would do,

Not exactly. Ford, unlike GM, was already in with the tach program pre '87. So when Ford restyled their trucks for '88 (the generation I'm familiar with), swapping a cluster with a tach into a non-tach truck was a plug & play deal from 1988-1991. GM? Nope, you had to add the wire and possibly move some around depending on the year as described earlier. Like GM though, Ford got goofy after '92. Despite the clusters looking the same from '92-'97 (F250's and such), you could not easily swap a cluster from say a '95 into a '92 without wiring changes, as Ford moved them around for whatever F'n reason.