I hate to say it, but what your considering is masking a problem. I may come back and bite you in the way of a fire while driving down the road.
A Cranking motor can draw close to 1800 amps with a cold engine. If you are going to go ahead with the idea anyway, I would isolate the power after the starter. You have to make sure that there are no other power paths. Backfeeds can cause all kinds of headaches.
Another hazard is if the switch fails while driving, it can cause a voltage spike that can burn out any electronics, like the alternator, and radios.
Far better to get to the bottom of the problem.
Friday, January 31, 2020 12:45 PM by