73 gauge cluster swap question

[Hertzdaddy]

I have a 73 Jimmy and I'm considering swapping in a 73 factory tach cluster. I have a few questions though.

Can I convert from the current volt gauge to the tach cluster amp gauge with a simple pin swap or is there more I need to do?

Can my electrical oil pressure guage be swapped in place of the mechanical one on the tach cluster?

If not, any mechanical oil pressure install tips/preferences?

Does anyone recall what other pin swaps are involved (ie fuel guage)?

And last, are there any factory options for a tach that goes higher than 5000 rpm?

Thanks.
Eric

[Captkaos]

If your truck is a 73, it should have a amp gauge and a mechanical sender, which is a 3 year only option. 73-75.

Has someone retrofitted a 76-77 (volt gauge mechanical sender) to your truck.  If so, it is going to take some in depth rewiring to convert it.

[Hertzdaddy]

The truck is a 73 but I guess it has been retrofitted. I'm not sure its a mechanical oil gauge though because I don't see the line going through the firewall. But the engine was removed before I got it so who knows where the line may have gone. I'll get up under the dash and check it out.

If it turns out to be a retrofitted 76-77 then what is involved in swapping over to a 76-77 tach cluster?

Thanks.
Eric

[Hertzdaddy]

Ok here are some picks of the cluster.



Its definitely not a mechanical oil pressure gauge. Also, the pin locations on the harness don't resemble any of the diagrams from 73-76 found on this site. 

Any help with year ID is appreciated.

Eric

[Hertzdaddy]

Ok I think I figured it out. It appears to be a 78 cluster and the pins have been rearranged on the 73 harness to fit the 78 cluster. In this case I would just need to map out the circuits on the repinned connector, diagram it to make it clear, and then re-pin the connector to mate up with a 78 tach cluster. Piece o cake! 

Does this sound about right?

Eric

[Captkaos]

That is a 78-up cluster.  There is no easy way to install that on a 73-75 truck because you can't use the amp pin to operate the volt gauge without melting the wiring.  Was this installed before?

[Hertzdaddy]

Yep. It was already on there. I didn't get a chance to see it run before the engine was pulled though, so I don't know if the volt gauge worked or not. I'll trace the wire and see where it leads.

[Hertzdaddy]

It looks like circuits 105 and 106 on a 73-75 are wired directly from the ammeter to the starter solenoid and the junction block and protected by 4 amp fuses. I'll eliminate those circuits by removing the fuses and/or pulling the pins at the cluster if they haven't already been pulled.

As far as getting a voltage signal, it looks like the 78 volt gauge just goes to the fuse block on circuit 39 for a switched positive lead. I assume I could tap a similar output on my 73 fuse block to make the gauge work.