I have a boat which is a center console.
When I give the boat’s engine direct power, it starts and the tilt trim works. But, when I connect the battery to the terminals, it’s no good – it won’t even crank over nor will the tilt trim work.
I have tested the isolator switch with a multimeter and it seemed to be fine.
What else do you think I should do?
Test the switch and cables with the engine connected while you are trying to start it.
It is very common for cables and switches to read fine with a meter, but as soon as you draw current down them, there is too much resistance in the wire/switch and the engine will not start.
Since the meter draws a very small current, it not cause the huge voltage drop problem that you are seeing.
Hope this helps,
So do you think I should buy and try a new isolator switch?
I would test the voltage at the battery switch when you are trying to start the engine. It may be the boat battery cables.