They make a tool called a Power Probe , that when hooked to.a battery you can touch the pointer on it to a positive terminal/wire and then depress the switch which will send power to that item . It will also put a good ground to that item if you depress the toggle the opposite way . Bad ground is the same as a bad positive . It also displays the exact volts that you are drawing from . Or make some long jumper wires and power up the engine compartment motor to see if it's good or on its way out .
