Originally Posted by
34nineteen
Or put a voltmeter across the battery terminals, try to start it and watch the reading. If the battery is faulty, it will likely drop the voltage very low when the starter button is pressed, as the starter motor will be acting as a makeshift load tester. If there is little or no drop, the issue likely is in the wiring/switches/relays etc.
Also, that jumper cable ground trick is very effective for bringing a grounding issue to light. My dad taught me that one back when I was a teenager with my ‘66 VW Bug chasing a really weird electrical problem. Turns out I neglected to attach the ground strap to the transmission and the electrical system was trying to complete the circuit through the clutch cable, accelerator cable and other parts.