Help with Oil pressure gauge, and other speculations

hey guys,

I recently picked up a 1989 mighty max with the g63b, manual trans. Dash says 186xxx. I didnt know much about these trucks when I bought it. I was looking for a small pickup to run around town in and found this little gem on craigslist near me in SoCal. When I went to look at it for the first time, I was pleasantly surprised. It had a FRESH paint job (a good one too), after market radio, A/C and heat worked great, no body damage alarm system....it was sweet. Once I bought it, I did a few things like replaced the water pump, new plugs/wires/coil/distributor cap, the oil pan was leaking so I replaced the gasket on it and got her all sealed up. From what I know now, it has a Sport gauge cluster installed and everything worked great except for the tach and the oil pressure gauge. I just got the tach working the other night by connecting a wire from the negative terminal on the coil to the screw on the back of the cluster labeled IGN -. So this got me thinking "Why wasn't the tach hooked up already? this gauge cluster must be an add on". Now my question is - If anyone has swapped out the stock cluster for a sport cluster, is there a way to get the oil pressure gauge to read on the cluster and how to do it. The truck has an oil pressure sending unit coming off of the filter housing. When I got the truck it had a small sender on it, and I've replaced it with a new large sender, but still no reading. Thanks for the help guys.

The only thing I can think of is that somewhere on the wiring harness the wire to the oil pressure gauge got cut or something. The wiring harness for these trucks already has the plugs to connect other accessories like the tach cluster, AC, and the like, so if it didn't work when you plugged it in I'd run down the wiring. It may also be a good idea to pull the gauge cluster out and look at it. They have one of those printed-circuit things on the back. You may check to see if the section running to the oil pressure gauge is damaged

The oil pressure sending unit needs to match the ohm of the gauge. The sending unit is a variable resistor. I'm not sure what the ohm measurement should be. But it should be listed in the first gen manual we have in the manual section.
To use the sport cluster you just need the cluster and there should be a plug under the dash already there.
If not you you just need to run the wires down. That info is in the first gen manual.