LT1 check gauges pin out / other stuff

[JD1964]

On the 94 LT1 pcm, is there a specific pin that illuminates the check gauges light on the instrument cluster? I’ve looked in the schematics and have not found it. Although I will have a voltmeter gauge in the car, I’m wondering if I can have the pcm light the gen light on the 79 Malibu dash as well.

I suppose the check gauges light could be lit by other things like low oil pressure or high coolant temp, but those stock LT1 sensors will not be used in this swap. Oil and temp gages will be old school mechanical.

I see the tach out signal pin. Can I use that to signal my old school Autometer tach or do I need to just hook the tach up to the coil as usual?

[NomakeWan]

The "Check Gauges" light is connected to the CCM and the Oil Pressure Switch. It's not connected to the PCM or any other computers in the car.

[lionelhutz]

Yes, check gauges is not a PCM function because the gauge sensors didn't connect to the PCM.

You can connect the MIL or malfunction indicator light (check engine) which is pin D9 or pin 9 on the blue connector. It grounds to turn on, so it could use the alternator indicator light.

[JD1964]

Thanks for the replies. Sounds good. I was contemplating using the Malibu gen light as the the new MIL indicator and one of my future questions was how the pcm triggered. Now that I know the pcm creates the ground I’ll use the gen light for MIL.

So, if there’s a problem with the battery or charging system, will the pcm recognize the condition and trigger the MIL to come on?

[NomakeWan]

DTC 50 is "system voltage low" and sets when system voltage drops under 8 volts. That's all you get from the PCM.

[JD1964]

Thanks for the info. An MIL at 8v is better than nothing

[lionelhutz]

Not much better, the battery will be completely dead before reaching 8V so there's no way it will still be running by the time the light comes on let alone run for a length of time after the light comes on.