Problems with starting, thought it was the battery

[wolfman]

I'll try not to confuse people here, but I know the more specific the better chance of troubleshooting. I have a 50HP 4 stroke Mercury on a pontoon boat. My wife went to start and the motor turned over like twice, but then the battery was dead (or at least power). They put another battery in, it started, they made it about 50 yards and it died. She tried to restart, nothing, made sure neutral, still nothing, so she go towed home. Later in the night she thought she'd try the boat again and it started, but kept it tied up. I came home checked the voltage on the first battery and it was like 12.3V. Put it on the charger and got it to 12.8, so I put it on the boat. Motor started, turned it off. Next day nothing. Pulled the battery and it shows 12.5V. Threw the 2nd battery on to see and it starts but I disconnected everything. I used to have a problem with something draining the battery, or kids playing with switches, so I never hook up the accessary wires, just the 2 main cables. So I can't understand if I have a drain with just those 2 hooked up. But with the battery showing OK voltage, why the intermitant starting or dying? Is there something in the gear shift regarding neutral? Alternator? Where is fusible link? It's really a pain to go find a trailor and get it in, so I'm hoping to be able to troubleshoot. Thanks

[brumbyvet]

It sounds like it might be your kill switch, maybe a loose wire. Or it could be in your electronic ignition, once it warms up it cuts off power.

[ToonGuy]

Sounds like a starter on the way out to me...

[badmoonrising]

How old are the battery cables ? Many times, a hole develops in the casing, the copper corrodes inside leaving you with a few good strands. Will fire up cold and as the remaining strands get hot, will not start.

I've seen this MANY times, in boats and vehicles.

[wolfman]

Thanks for the input, I have figured out a few more things which will either help things or complicate them. At first when started the tach would show 4000rpm while idling, usually around 1500. I replaced the fuse on the accessory (+) cable even though it was good just corroded, and connected the accessory cable also. All the lights worked, radio worked, but no horn, and...it wouldn't start, no trim either. Disconnected the accessory cable and it started and trim. So that must mean something is shorting that out? The dealer out here said muskrats have been chewing up wires, so I looked underneath and sure enough, part of a wire is eaten to expose a small piece of wire, which was under water. I can't follow the front of the wire, but the back end goes down to the lower unit, it's about the diameter of a pencil. (What is that?). So then when looking at the wiring behind the dash, I did see a brown wire hanging with an exposed end. I can't tell where it went, it's under the radio and behind the speedometer and ignition. I'll try to post a pic to see if you happen to know. So I did find a few things out, the only problem is these things were happening even before I hooked up the accessory cable, so I don't know if it's related or another problem. Put a meter on battery 12.7 off, like 13.4 running, and tach is showing 1500rpm