SES light problem

[88 Beater]

I've been trying to chase a problem with my SES light. It's a very strange one. When I first started working on the truck, the SES light would not come on but bulb checked out ok so I looked in the ECM and it had a burned up IC. I replaced the ECM and still no SES light. I tried jumping the A & B terminals on the ALDL and got the light to come on and show me a 12. After that, the SES light came on when turning the ignition switch on. Started the truck and drove it around the block a couple times. It ran slightly better but still pretty crappy. Now the SES light doesn't come on when turning the key on.

I took the bulb out of the instrument cluster and used an analog voltmeter on the bulb socket contacts. It shows voltage when I turn the key on and it shows me 12s when I jump the ALDL but there just doesn't seem to be enough current to light the bulb. BTW, I checked the bulb by hooking to the battery and it lights so it's good.

I'm thinking I have a short somewhere that's letting a small amount of current get to the bulb but bypassing it when an actual bulb is installed. Any other ideas? Any ideas on where to look for the short? I'm not looking forward to tearing the dash apart. Hope I didn't burn up my new ECM.