My 1989 f-250 7.5 2wd has a rear antilock light that comes on when I get up to 40mph and stays on until I shut the key off. I have found a thread that said to check the brake fluid (done that) change ABS sensor on rear end (done that) check fluid in rear end (done that) all ok. We have found that the pinion nut was loose so we tightened it up. There were fine metal shavings on the magnetic plug on the rear diff we have been watching it closely. I hope I'm not losing a rear end.

 

Solution:

Step 1: pull the dash light cover

Step 2: pull abs bulb

Step 3: reassemble dash

 

A loose pinion nut is bad news, and usually indicates bearing damage. Does your speedometer work correctly? Does it bounce around at higher speeds?

 

The speedometer works perfectly and my dad has 2 other fords and had to tighten up the pinion nut on them too. He believes that it is common for those to back off after time, but like I said we are keeping an eye on it.

 

Try bleeding the ABS unit.

 

From Steve83:

Flashout Codes

Whenever the yellow REAR ABS light comes on during normal operation, a flashout code may be obtained to aid in problem diagnosis. If the vehicle is shut off before the code is read from a RABS-I module, the code will be lost. In some cases, the code may reappear when the vehicle is restarted.

More information:
RABS Codes

RABS Flow Chart

RABS Troubleshooting

All courtesy of Steve83

 

Ok I will look into this, my grandpa has a OBD1 ford Lincoln Mercury code reader.

 

That will not work to read RABS codes. Read the info in the links I posted earlier.

 

Ok, where is the RABS diagnostic connector usually located?

 

Read the information in the links. Most everything is there to answer your question.

 

You'd be done by now if you implemented my solution, just sayin!

 

This should help locate the test lead: Pulling RABS Flashout Code. This routine should be good from 87-92.

 

+1 for 89F2urd's solution and I would add pull the ABS fuse out of the fuse box. RABS on these trucks is dangerous, IMO. Mine has been disabled for about 10 years or however long I have had this truck.

 

Best thing you can do is just unplug rabs module believe me!

 

What makes them dangerous?