inop Anti-lock/O/D light

Have a '93 T100 long bed with 260k on it. Great reliable truck, except for the usual problems - seatbelt retractors, chintzy door locks, and sedate engine. I have a couple that I'd like some feedback about:
1) O/D light on the panel flashes sometimes - a leisurely 1 flash every couple seconds. Auto of course. When it starts flashing, it continues until I stop, and shut down. Then it doesn't come back on for a few trips. Tranny seems to perform okay, O/D switch works, downshifts as it should, etc. Fluid is okay. Can't find a reference to this flashing light in my Haynes book and my mechanic is clueless about it. What does it mean? Any experience with this?
2) Rear anti-lock light has been on since I bought this truck a couple years ago. Rear brakes work nicely, except on wet surfaces. Then it can become somewhat tricky -just like the old days in my '83 mazda SE5. I actually put some concrete pavers in the bed just inside the tailgate on wet days to keep my taillights facing generally aft as I brake for traffic signals. Anyone got experience with that problem?

Thanks for any ideas you might have.

The flashing O/D light means you have a problem code stored concerning the transmission. It's probably the speed sensors but I'd put it in diagnostic mode and pull the code to be sure.

Also, make sure yer battery is up to snuff as it can cause other sensors to indicate failures because of the low voltage.

You'll need to pull the diagnostic code fer the ABS... ;) If the speed sensor circuit isn't functioning...it could be the cause fer both systems to not function properly. :(

Are yer back brakes locking up? Are you sure the LSPV (load sensing proportional valve) is working correctly? Block the front wheels and jack up the rear by the differential. Release the parking brake and spin the rear wheels. Step on the brake. Are the rear wheels stopping? ;)