i am trying to put a 91 instrument cluster in my 88 gxl. the problem being the 91 has three plug-ins and the car has only two plugs. i suspect the problem maybe the fact that the 91 is from an automatic whereas my 88 gxl is a standard. i thought if i could figure out which two plug-ins to use i might be able to use the 91 instrument cluster. any help would be appreciated.

i think that 3rd plug is just for the 'prndsl' lights

I heard the S4 gauges are more accurate.

Ronin's right. The temperature gauge on an S4 is more linear, whereas the S5 gauge is center weighted (like most other modern car gauges). The S5 gauge can be made to work in a linear fashion. The San Diego Rx-7 Club website has a “how to” write up.

that is if the sensors and wiring isn't old and faulty...