ABSlight and Brake light come on and off, but

Some vehicles speedometer works off the ABS wheel sensors. Have the codes checked for the ABS system. Check the fuses for the ABS also.

Try checking for codes....no speedo with other problems usually vss (vehicle speed sensor) shot

If the red brake light and the ABS light are both lit up on the dashboard, do NOT drive the vehicle. It indicates a major malfuntion with the brake system. The red light indicates low brake fluid or the parking brake engaged. The yellow ABS without the red light, indicates a problem the computer found and it disables the ABS system while still having conventional brakes. Since both are lit, it needs the brake system repaired. What you replaced on the rear diff was probably the rear ABS sensor. The vehicle speed sensor for the speedometer should be located on the rear of your transfer case if you have 4WD, or on the rear of the trans if you have 2WD.

Fuse 12 (10 Amps) may be burned out. Its located in "Junction Block". Losing
fuse 12 would kill the ABS systems and light the ABS dashboard light.

Fuse 11 (20 Amps) may be out. Its located in "Power Distribution Center". Losing fuse 11
would kill the brake lights, and light the ABS dashboard light. If fuse 11 is blown,
check your (3) brake light sockets for shorts of any type, or fuse 11 will just blow again.

Here's your ABS Indicator Light wiring diagram:

Possible problem with one or more wheel speed sensors, or the vehicle speed sensor, or the related wiring connections. I have found rotted out wiring harnesses or connections on wheel speed sensors numerous times. Hope this helps.

Brake light probably means that either your pads are low (if your truck has wear sensors in the pads) or that you have a brake/taillight bulb out. The ABS light is because either you have an ABS/wheelspeed sensor that's gone bad or the ABS actuator is bad. That should be able to be cleared up with a scan of the car's computer. If the module is bad, it's usually very expensive to buy one. Check out www.modulemaster.com - many of the guys in the Audi world that I know have had ABS modules rebuilt for $200 or less, and returned within a couple days, with a warranty. They have a great reputation.

Probably either your PCM or Vechile Speed Sensor. The VSS sends an AC (alternating current or sine) wave to the PCM and according to the frequency of the wave, tells the PCM the speed with which the vehicle is moving. It will be mounted to your transaxle, and I would look into this before the PCM.

sensor in rear diff may need replaced

The first step in diagnosing this problem is to hook it up to an ABS scan tool and see what trouble codes it has put out.

No definately the speedo....