Have a 88 40hp evinrude and every time I hook up the motor to the battery it blows the 20 amp fuse under the hood. All the wires look good and replaced the ones that didn't. Think it may be the battery cables. Tried two new batteries and same thing happens. Has anyone had a similiar problem. If so lend someone who just wants to go fishing some advice. Thanks in advance.

You got a ground short. Start looking for breaks/worn spots on the battery cables any place they MIGHT come in contact with the metal. Chances are good that your 14 year old cables are ready for the trash bin. Could be a ton of other conponents such as start solenoid, starter, rectifier,stator,etc or any of the wiring connecting them. Hope you'er good with a multi meter! Naturally, do all checks with the battery disconnected or you may have a shocking experience

Yeah what I suspected, Luckily I am decent with a multimeter. Where can I get some new battery cables? All the ones I have seen are too short. Probably have to fabricate them myself. Thanks for the reply.

Ebay has alot of new cables from 2-25' in sizes from 6 gauge on up..cheap. Make sure and get them in marine grade or you'll be replacing them fairly quickly. Acad might have some locally. Of course , a marine dealer will have them for high dollar. Use dielectric grease on alll connections.

There are also some wires that go from your throttle control to the motor that if they are shorted they will blow that fuse when you hook the battery up. you should probably check your whole wiring harness, starting with your main battery feed. have fun...