Quad drivers operate high load components like cooling fans, egr valves
solenoids, tcc solenoids and the like, you need to look at all the
solenoids controlled by each quad and eliminate the circuits until you
pinpoint the copmponent. This may not be a job for a dyer, without a good
diagnostic trouble tree like Alldata provides. Look for pinched or burnt
wires where you last woked on the car and other related components. Also
next time post year make and model/engine!