Dual battery switch failure?

[dawils]

My engine will not start on battery 1. Clicks like weak/ bad battery. Charged it. Tested it w tester. It's fully charged. Mechanic said to check ground. Looked ok. Said it was likely not bad switch because they usually fail totally. Battery cable connection cleaned and tight. Same. Battery 2 when switched is strong. Seems like must be a bad switch. Any other suggestions? Thank you!

 

[dingbat]

My engine will not start on battery 1. Clicks like weak/ bad battery. Charged it. Tested it w tester. It's fully charged. Mechanic said to check ground. Looked ok. Said it was likely not bad switch because they usually fail totally. Battery cable connection cleaned and tight. Same. Battery 2 when switched is strong. Seems like must be a bad switch. Any other suggestions? Thank you!

Not sure what “tested with tester” means. Was it load (amperage) our voltage tested?

Could have burned the contact on battery one side. Switch battery wires on back of switch to see if problem moves from one battery to the other.

 

[Scott Danforth]

so wire battery 1 direct bypassing the switch. if that works, spend $30 on a new switch

 

[alldodge]

Mechanic said to check ground. Looked ok.

"Looks ok" I think the mechanic has the right answer.
Remove the dang cable from the engine block and battery. Look under the insulation jacket for corrosion