How to clear FX3 codes?

[BlackbirdZ07]

I just did a search and couldn't find the details I need... Service Ride Control light in my '90 is on, and when I pulled the codes I found that ALL the codes were set. I think I may have caused that by connecting an almost discharged battery. I'd like to clear the codes and start over.

The FSM only says to ground pin C of the ALDL for two seconds and repeat twice, for a total of three groundings. I've tried doing that many times but no luck... can someone tell me exactly how to do it? I tried turning the key on with the ground in place, leaving it for two seconds, removing it, etc. so it was grounded three times. I've tried waiting for two seconds after code 12 starts flashing. I've tried turning the key on and off three times. I've tried turning the key on and then grounding it, etc.

I also tried disconnecting the battery overnight and driving the car, and nothing has cleared the codes.