gauge cluster wiring

[sweat90lx]

my car is a 90, my gauge cluster is from an 89(it was free)
i had an 85 mph speedo and my tach was way off
i have the wiring diagrams for both 87-89 and 90-93
my question is i dont want to rewire all 28 wires, i know i will have to rewire 2 grounds, high beams, both blinkers, illumination; can i leave everything else the same or should i cut the rest(i have mechanical water temp and oil press)
my altenator has stopped charging, is this because its grounding in this cluster?

 

[trbkrb]

Is the 89 cluster a 140 MPH V8 model unit? If so, I'd sell it and buy a 90-93 unit that will plug right in. You could probably make some money on the deal and get the correct fitting cluster. Especially since the 89 model may not fit right with the airbag steering wheel (flat bottom vs arched bottom to clear the later model steering colum).

And yes, the cluster completes a circuit for the alternator, signalling it to charge the battery.