little advice
Do you have access to the wiring diagram and a multimeter? You can throw parts at it and that might find the problem eventually. That's going to cost you alot of money and time. It's a bear to take that brake system apart and bleed. I've been there. I had a grounding problem at my motor relay which was caused by defective pressure switch not grounding the circuit. It took me about an hour and half to just replace that switch(that include walking to the cooler for more beer)Diagnosing the problem will take a couple hours, but that is time not spent wating for parts that you might not need. Good luck and just remember, some guy put this ~~~~ together once before. Just figure out how it works. mike