Help! Check engine light

[harleysprocket]

I have a 1981 Vette. The check engine light stays on when car is turned off and key is removed. When motor is running the light goes off. I replaced the ECM but it did not fix the problem. I have to disconnect the battery so it want run down. Any ideas???????

 

[Antz81]

The check engine light is powered by the gauges fuse. And is switched on by the ecm providing a ground to it.

The guages shouldn't have any power after the ignition is switched off. If they have a 12v the engine keeps running, so you only have a low voltage there.

Unplug the two pin plug on the alternator and see if it goes out. If it does you have a problem in your alternator.
if that's not it then you need to find out where the voltage on the circuit is coming from. (A short to another circuit or a faulty ignition switch.

 

[harleysprocket]

I pulled the plug on the alternator first thing but light stayed on. with car not running and key switched off and light on, I pulled the wire harness connection to the ECM off the terminals and light stayed on. I think all the gauges are off when light is on but not sure, will check when I get home from work.

 

[Antz81]

I pulled the wire harness connection to the ECM off the terminals and light stayed on.

Which wire harness are you referring to here?