My neighbors ,97 dually has an ABS light on all the time. I plugged my OBDII scanner in and it did not show any codes. He has an analog odometer so there's no chance for the key trick. Any suggestions? Is this maybe an OBDI or something.

 

No OBD2 first look for the simple things like a leak in the vacuum lines check the dash controls if his air and heater blows out the winshield vent all the time its a leak in the vacuum sys if it don't it is the ABS sensor in the diff hsg right on top of the diff hsg.

 

my 98 does the same thing, its been 4 years now. does he hear a ticking up near the mastercylinder when the brake pedal is pushed in? I can hear it on mine. every one thinks Im nuckin futz. but the noise goes away sometimes.

 

Does it have RWAL or 4WAL ABS?
He will probably have to go to the dealer and get it scanned unless somebody knows if there is a trick to jumping a few terminals and getting the light to flash a code.

 

Check the fuse's mine came on and it was a blown fuse

 

I checked the fuse on the side of the dash, it's good. We looked under the hood and there was no 20 amp fuse where it showed one on the diagram. He said it never had one so that's not the problem. I think it's only RWAL because there's no relay under the hood either. The light will be off when the engine is first started then it comes on as soon as the brake is applied. The speedo works so I'm not concerned with the wheel speed sensor on the diff either. Could this be worn rear brakes? He said he hadn't had them done for some time and he pulls a huge fiver with this rig. Thanx for the replies folks..