If my brake light and ABS light come on in my dash and I think that it might be the vacum pump how do I test the pump??

 

You will know when you apply your brakes. If you keep steady pressure on them, they will work properly. If you pump them and the pedal gets extremely hard with NO stopping power, you can bet its your vacuum pump. You can also start the truck and pull the line off of the back of the pump, I don't know how much vacuum it should pull, but you'll know by putting your finger over the hose. It should grab your finger pretty good. Mine had very weak suction, I put a new pump on it, (about $125), worked like a charm.
That was on my 97' F350 PSD.

 

On the 7.3 IDI it should be about 20 inches Hg.

Torstein