The 1991 350 SDL (anti-slip differential) has a problem. The dash light does not go out when engine is startes (it should). When on ice the small light within the speedometer does not light when wheels spin (it should). Also, the system does not work.

In attaching an electronic tester, it indicated that the brake switch was bad, we replaced it and get the same report. Next we replaced the relay with the two red fuses, still get same report and system malfunctions. We did all prescribed voltage and continuity tests and all components seem to be OK. We suspect the about $500 computer for the system but do not want to replace it and find it is not the problem because it is not returnable. Any help out there?

Bob