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ABS Light

Michael:
I'm not an expert on blinking codes of ABS lights, so someone else may have a better diagnosis, but...
Early Oilhead with ABS light on is pretty common. I'm gonna guess it's the battery. If your start pulls a few too many amps on a weak battery, the voltage goes down to the rest of the system momentarily during the starting process. This kicks on the ABS light. This early version of ABS had no tolerance for low voltage.
The temporary solution is to warm up the bike and let the battery charge a little by riding around (assuming your brakes still work) then shut it down and quickly restart. It should start without the ABS light coming back on. If it does, it indicates a weak battery. Replace it because it'll just keep getting worse. 

DON'T TRY THIS AT HOME:
I had a battery go down during a trip in colorado and I friction-started my '99 RT. This method starts the bike without the help of the starter motor, so no low voltage unless your battery is really dead.
Get the bike rolling with key on, drop the clutch in 4th gear, then pull clutch in when the motor starts.
If you've already started the bike and want to get the ABS light off, keep rolling, (any speed above 10 mph) pull in clutch, turn off ignition, turn on ignition, let clutch out momentarily to start engine. (This is completely unsafe if there is any traffic around, so use good judgement.)
Warning: Use 4th or 5th gear to do this. Low gears will cause the rear wheel to skid when you drop the clutch. So long as the bike still starts normally, I'd just do this procedure at 30 to 50 mph after the bike has warmed up. With practice, you can do it really quickly, barely losing pace.
I don't think the early ABS needs the bike to be at a standstill to reboot. If it does, you have to pull over and restart the bike with the starter when it's warmed up...starter will pull less on the battery than it does with a cold engine, but it's not as good as friction-start, battery wise.
Both ways are band-aids, but they work. Won't cure the problem, it will just get your ABS light off until you can get a new battery.
My bike turned over very hard one morning while I was touring. ABS light went on. I used this method at 50 or so to get the light off. Next day, in Gunnison, CO, it wouldn't start at all, so we pushed it and I used this method to start the bike cold...lots of work. I used it at gas stops etc all day. One learns to park pointing down hill.
I was on my way to Top o the Rockies rally. When I got there, I bought a battery and installed it at the motel. Next day, I brought the old one back to the dealer for recycling. No more problems.
Do you recall that last battery thread? It was mostly about the new Gel/AGM batteries, but there was some mention of Wesco and Panasonic batteries. The Panasonics seem to work OK, but the Wesco doesn't (or didn't in the old days) have the cranking power to keep this ABS light from going on. Many people with your vintage bike have seen the ABS light problem with brand new Wesco batteries. I don't know if Wesco has fixed this problem or not. BMW AGM batteries and Oddesy batteries work well. I have a friend who liked his Panasonic battery on a '96 RT.
I don't think you'll find any BMW lead acid batteries around anymore. They're all AGM now. Special charger needed for major charging, but I think the small trickle chargers still work for topping them up occasionally in winter.
Your problem could have some other cause, but I doubt it. I'll bow to superior technical people in an instant on this. The slightly weak battery/ABS light problem is really common on early Oilheads though.
I'm remembering that there was an update to the ABS system beginning with '98 models that made ABS less volt-sensitive. Even in my '99 RT, the light would go on during a start in really cold weather.
To my knowledge, you can't update the ABS system to the '98 spec easily. It would involve replacing the ABS unit completely...big job for small, manageable nusiance. 

Hope this helps,
-TB