I turned 2 junk trucks into one. Everything electrical and mechanical wise is currently from the 94 except for the dash wiring harness and gauge cluster which are from the 92.

Everything is working but the tach and the speedometer. The tach will jump from 0-3k when you hit the gas and eventually go straight back to 0. The speedometer just stays at 0. The harness from the 94 was hacked up beyond repair before i got the truck. The only two connectors not hooked up are on the passanger side in the engine compartment, which i believe are only for abs and air bags. The 94 did not have these connectors and the gauges worked just fine.

the 92 transmission is going in before winter. Are there any differences besides the vacuum vs electronic transfer case?

 

The 92 speedometer is cable driven. Just get the cable that comes from the transfercase. The speed sensor is swappable.

The tachometer could be just a bad connection or a bad ground or power supply.

As for the transfercase the vacuum is only for the CAD Central Axle Disconnect which the 92 has but the 94 doesn't. 93-down had CAD. Depending on which front axle you have, if you have the 94 then you can delete the vacuum system, but if you use the 92 axle you will need it.

The electronic part of the transfercase is just a light switch for the 4wd light shift bezel. I believe on the 92 it is on the front axle.