Two battery switches

[Bobkat]

I have a 72 with 454 Crusaders two batteries and two battery switches.
No one I have asked can explain why two switches. Both are on-off-both. I have left them both swithced on both.
If anyone knows I would appreciate some help.

Also if there is a good reason for two switches a proper wiring suggestion would be really helpful.

She was repowered by the previous owner who knows if they were hooked up as they should be.

[Bruce]

If you want to isolate the engines from each other, then two switches are needed.

If you had one switch and had an electrical short on one engine, you would have to shut both engines down to disconnect the battery, leaving you stranded.

If you leave the swiches on both and have a drain on one battery, it will drain both.

With the both style switches, if your primary battery is dead, it allows you to connect to the good battery to start.

The way I wire them is #1 is the primary battery for each side. #2 is the opposite side battery.

That way you just leave each engine on 1 instead of both.
You'll need to check the wiring to see how they were wired. I have seen all kinds of crazy stuff.

BTW the common terminal goes to the engine.

[In Memory Walter K]

Basically, you have two independent dual battery systems. You should/could start the engine on either battery 1 or 2. Should your battery for any reason be discharged to the point that you can't turn over your engine, you can switch to the other one. Neither side of batteries affects the other. "Both will charge them both. Walter

[Skipper Dick]

I have a 4 battery system. Two batteries are for the port and stbd. engines and two batteries are in parallel for the house battery. All three circuits are isolated by a battery isolator and I have a battery switch for each circuit. If the port battery dies while out 50 miles, I can switch to both and draw current from the stbd. battery to start the port or visa versa. The two house batteries are independant of either the port and stbd. battery. Each circuit iis fused by a Blue Sea 50 amp breaker and the stbd. battery powers the bilge pumps direct through a separate circuit breaker bypassing the battery switch..

It sounds a little complex, but it really isn't. The only thing I'm not happy about is that I started with group 24 instead of group 27 batteries. I did use group 27 battery trays though.