2004 f350 6.0l. Abs light is on cruise doesntwork andspeedo doesnt work.

?????

 

Maybe VSS (vehicle speed sensor)? Think it's in the rear differential.

 

I think it might be more than just the vss, or even the harness. If there is a failure in the rear vss, the pcm then looks to one of the front abs sensors for speed input. And the cruise should work while the abs light is on(that is, if its your rear vss). The cruise and speedo will momentarilly not work with a rear vss failure, but then will start working when the pcm starts looking at the front sensors
for input. At least that was how my truck acted when my rear vss harness went bad.

 

I can't speak for your truck, but there have been many, many reported cases of a failed VSS causing the speedometer to quit working, the ABS light to come on, the Tow/Haul light to flash and the transmission shift patterns to go to hell.

In most cases, replacing the VSS solves this problems. In fewer cases there is a wiring harness issue.

At least that's what I've observed over the years here. The VSS is held to the top of the differential case with one bolt and is not difficult to change.

 

Does any one know how to test the vss

 

About 8 months ago, I had the same problem. I replaced the rear VSS sensor and spent countless hours pinning the harness. Finally gave up and took it to the dealer, turned out to be a burnt circuit board in the windshield wiper motor.
Sounds strange, they replaced it and I haven't had a problem yet.