The SES light has been coming on and off in my Bonneville lately. It tends to come on when I'm on the gas, and usually turns off in about 10-20 seconds when I take my foot off the gas and brake down to a fairly slow speed. I dug under the dash and did the whole paperclip trick to read the codes and it just gave me a code 26 (Quad driver module "A" Circuit )... which is great... but what the hell does that mean? Thanks.

Well, on the 93 it is telling you that you are receiving an incorrect voltage from:

1. Charcoal canister purge solenoid
2. High temp lamp
3. Low speed fan relay
4. Brake switch
5. Torque converter clutch apply solenoid.

Not sure if your year is the same.

'89 .. yeah, beats me too.

Number of electrical failures will trigger a 26 but most will also set a different code. (TCC will usually also set a 39).Exceptions are the cannister purge line and a cooling fan failure (fans not operating is usually pretty obvious).