1990 Crew Cab Dually

[TravisMartin]

I just picked up (rescued, really...it was being abused...) an R3500 with 454 and TH400 and most options. Drives pretty good but has been cowboyed almost to death. Planning to bring it back to nice if I live long enough.

It has had an aftermarket mechanical oil pressure gauge installed...I can't find the wire from engine harness for the oil pressure sender. I believe it is a tan wire, but the sender is gone...where should it be mounted? The mechanical gauge is connected just above the oil filter. Doesn't a TBI motor have to have an oil pressure switch to maintain the circuit to the fuel pump? It runs fine and I hear the fuel pump relay click after a few seconds after the starter has been operated so I'm assuming the oil pressure switch is there...but where?

Next question...it would be a far more enjoyable truck with a 4L80E in place of the TH400. Has anyone done this swap with original components, much like the fairly common retrofit of TBI into carbureted trucks? Looks like it shouldn't be a big deal if you had a 91 up donor. Is the transmission controlled out of the ECM or is there a separate box?

Thanks,

Travis