Hello. Im steve, got a 1990 chev. Suburban gas 4x4, speedo is working, power to pink/black at panel, no sings of vaccum leaks, external condition of servo is fine. Truck is not rusty, verry good condition. Just got it from florida. The abs light must of been lit, they did something to the wiring in the surrounding of the booster and main connector at fire wall (wondering if there is something to do with it)i removed the rest of the system for passing inspection purpuses. Ive got a scematic but no explanetion for diagnostic, I am a truck mecanic with good skils to find that problem but_____ hopefully you could give me a hand with youre knowledge or direct me to a most complete trouble shooting shart. Thanks alot for your help, your time and professionnalism. Ps sorry for my hand, im french.