a clamp model 12 v ac dc ammeter solves a lot of fussing around while trying to diagnose weird things (like why the on deck windlass quit working... why all the 12v lights blew... ) don't buy the fluke ac dc voam w clamp ac dc amp function, $340, mine kicked the bucket just after the 1 yr warranty expired. ' " ( clamp function is not repairable, said fluke: we'll give you a discount price of $220 on a new one..' )