Mysterious electrical problem on a 1988 mercruiser 4.3

[Classic88]

Im restoring this old boat and am running into a phantom electrical problem. Some gauges aren’t working, but in investigating, I’m finding that their power supply is fluctuating and maxes out at something like 11.2 volts with the engine off but a fully charged battery. The bilge pump is new but only sometimes can pump strongly enough to clear the bilge, so I’m assuming this is a power problem too. Where should I look to try and track down the source of the difficulty?
thank you!

 

[GA_Boater]

Clean all power connectors, including grounds. Sounds like an electrical corrosion issue or loose connection.

 

[wellcraft-classic210]

Yes -- not to b overlooked on checks is the ground wire back to the engine -- often bolted on the port motor mount

 

[Bondo]

Clean all power connectors, including grounds. Sounds like an electrical corrosion issue or loose connection.

Ayuh,....... Welcome Aboard,...... Especially the grounds,.......

All yer connections need to be clean to shiny metal Clean, from the battery, onward,.....

 

[Classic88]

Thanks, everyone, for these great tips. I’m cleaning connections and think there’s already an improvement. But here’s a question: I’m noticing that voltage is about 12.6 at the fuses at the helm, but after the ignition it drops to about 11.6. Could this mean a faulty ignition?

 

[Eastboundndown]

Im restoring this old boat and am running into a phantom electrical problem. Some gauges aren’t working, but in investigating, I’m finding that their power supply is fluctuating and maxes out at something like 11.2 volts with the engine off but a fully charged battery. The bilge pump is new but only sometimes can pump strongly enough to clear the bilge, so I’m assuming this is a power problem too. Where should I look to try and track down the source of the difficulty?
thank you!

Sounds like a bad ground to me. I would make sure you have proper voltage at battery 1st to rule that out then I would unmake, clean and remake any ground terminals and or connections that look suspect.

 

[Eastboundndown]

Thanks, everyone, for these great tips. I’m cleaning connections and think there’s already an improvement. But here’s a question: I’m noticing that voltage is about 12.6 at the fuses at the helm, but after the ignition it drops to about 11.6. Could this mean a faulty ignition?

Bad connection on load side of fuse panel. Either 1 of 2 issues. Either load side terminals of panel are compromised or bad terminal connections.

 

[GA_Boater]

One way to chase ground faults is to use a long piece of wire connected to the ground post on the battery. Use the wire as the negative for your meter and set it on a low OHMs scale. Probe the the ground connections with the positive meter lead. You are looking for high resistance.