1985 Johnson 140hp 2 stroke - no electrical power?

[louisorr]

G'day!

My 1985 johnson 140hp 2 stroke outboard is having some electrical issues that are quite difficult to describe but I will try make an effort to explain it as simple as possible...

Basically, the engine does not seem to be reacting to the ignition being switched on - at least most of the time. Every now and then while I'm playing around with the engine trying to work out what's wrong, it will spring to life, in that the analogue volt meter on the dash will bounce up to 12.8V and it appears that everything is fine, however, this may only last momentarily OR if i try start the engine or use the trim switch, it will instantly lose all power and the volt meter bounces back down to 0. When I do try start it, if I'm lucky enough to have the engine react to the ignition being switched on, I hear a loud spark come from the outboard and all power is again lost.

I'm inclined to assume that this is an electrical short but for the life of me I have not been able to figure out what is causing it! Any help would be greatly appreciated, I understand my explanation of the problem isn't very detailed but it's very hard to explain as there is no apparent pattern as to when the motor will or won't react to the ignition being switched on.

Thanks!!

PS, i have tested both the starter motor and solenoid and they are working.

[boats.net]

I would start by getting a battery load tester and load test battery and see what voltage reading is, should be 10 volts or higher. Then connect load tester positive lead to positive battery cable at starter solenoid and negative tester lead to engine ground cable to see if get about same loaded voltage as at battery. This will test condition of battery and battery cables, then look at red wires connected to solenoid and regulator for shorted or broken wires. Then test if have battery voltage between red and black wire at key switch and if have battery voltage between purple and black wire at key switch when key is in ON position.