I know this is old thread but my brake/ABS lights went on too. Speedo is working fine and not throwing any codes.
I rekon my sensor needs replacing. This is a combo sensor? (ABS / Speed sensor)

When that was happening to my truck (ABS + Brake Lights on), it ended up being because of bad wheel cylinders.

Just food for thought.

Also, if those lights are on, you do not have ABS.

I did remove the rear proportional valve to install air springs.
I replaced the valve with a hose.
When I bled the brakes, I had a bleeder that was plugged up. I will try bleeding the entire system and replace the bleeder and see if that helps.

huh? ..........

Didn't some of them have a height sensing proportioning valve on the back?

Yep. I removed mine and put in a brake line per TSB.

Yes, my 2000 has that. I replaced it , with the same part from Minton Motors. Not a hose. (whatever that means).

http://dodgeram.info/tsb/1998/05-04-98.htm

Removed valve and rod because I installed air bags.
Installed 52009575AB HOSE, Brake

OK, sorry. You should have said/posted that to begin with.

No worries! Hard to explain. I should have!

Anyway. My manual say the module stores a code. I have to disconnect the batteries to get the light to go out.
Says to ground something and then count the flashes. Manual does not tell me what to ground but gives me flash count codes.
Any ideas anyone!