|Can't say if your ABS system is the same as mine,but... |My 99 F150 ABS light went on steady. Been like that for 1.5yrs. Finally got |info from a CarX shop. |Since mine has no connecttor to read the codes, I had to find a black wire |with an orange stripe in the harnesses in the passenger kick panel area. |Disconnected it. connected a wire to it. |Grounded the wire after turning key to run ( did not start engine). |ABS light begins flashing. |Count the flashes ( including the long one on the end. | |Mine was 9 . |As Bomar said, it was the rear differential speed sensor. |cost all of $13. |The big problem was finding a parts place that had any idea what I was looking |for. |AutoZone wanted $40. Even CarQuest was asking $36. Fortunately the CarQuest |part never showed up and a different counter man located the right part . And |it was cheaper.
Monitoring this thread, as my '94 has the same problem as the OP. Looked up the diff sensor, jobber price is $13.84 in Raybestos, and it shows to be selling pretty well. I'll just grab one and skip the wire-cutting part. Thanks for the tip.
Rex in Fort Worth