Power drops at console when hitting switch/turning ignition

[dieffer]

HI all- Working with a 1990 Larson All-American 170 with a Mercruiser 3.0 Litre engine. Something was draining the battery and causing issue with starting. Now none of the switches work and nothing happens when you turn the key. I'm getting 12.7 volts at the fuse box under the console, and if I unplug the 8-pin wiring harness coming from the back, get 12.7 volts there as well. However, as soon as any of the switches is flipped or the ignition is turned to the run position, power readings at the fuse box drop to 0. What would cause the power to drop like that? Needless to say the result is that nothing on the boat is working other than the trim. Brand new battery, reads 12.7 volts at battery.

 

[dwco5051]

If you haven't done it already remove and clean your battery connections. Sounds like a corroded connection or the main wire off the battery is corroded at the connector. You have just enough of a connection to power a voltmeter but any higher amp draw fails. Just ran into the same type of thing on a motorcycle making it's first run after sitting in the garage all winter.

 

[mike_i]

Go back and measure the voltage at the battery while cranking the motor to confirm the voltage is stable at 12.7ish and not dropping.