Resolved Power to CAS 1g location

Travis Grant · Apr 29, 2026

Hey guys, I’m missing 12v going to my CAS on pin 3 at the connector.

I was trying to search on the forum and can’t find where pin 3 gets power from. I’m sure it comes from the MPI relay but can’t find which pin. I have power to pin 10 at the relay which is fed from the MPI fuse.

Any help is appreciated! Thanks !

Tyeler18 · Apr 29, 2026

Pin 4 or 5 from the MPI relay supply the CAS 12v, they're red just like pin 3 of the CAS. It also supplies the o2 sensor, injector resistor, all the emissions solenoids, ECU and majority of the engine. If you're only missing 12v at the CAS I wouldn't bother testing at the MPI because your open is somewhere well down the line from there.

steve · Apr 30, 2026

I posted these a while back in https://www.dsmtuners.com/threads/1990-engine-ecu-mpi-circuit-diagrams.540595/ but perhaps you didn't find them.

You can see on page 73 that the MPI relay sends power when it's on to the ECU and to circuits off that page marked "A" which is on page 75. That's where it's shown that it goes to pin 2 (not pin 3) of the CAS (We are talking about a 1990 car right or have you converted to the 91+ CAS?)

It would be helpful if you had profiles for you vehicle(s).

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Travis Grant · May 4, 2026

thanks for the responses yes I did switch to a 91+ cas. Ended up finding the corroded wire from pin5 at MPI relay to pin 3 at CAS. Very much used to looking at GM wiring diagrams on much newer vehicles than I am at following old school paper diagrams LOL

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Resolved Power to CAS 1g location

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