1982 mcm 898 high voltage going to ignition key switch

[Vipguy87]

i replaced my ignition coil, spark plugs, rebuilt the distributor and carburaetor due to a no spark situation. I then replaced my alternator because I wasn't getting any charge out of the old one. took the boat out and everything was fine. We were cruising about 40 mph and the boat just completely died. I open the engine cover and discover that the purple wire coming out of the engine harness going up to my key switch is melted and smoking through the whole thing. get the boat back home and discover that the purple wire that fried is reading about 14 volts while the motor is running. the coil reads 6.5 volts when running. what could be causing this?? I replaced the wire completely from about 2 inches out of the harness all the way to the key switch as well as replaced the key switch and same deal . I'm stumped. also when the boat is running and I turn the key off it doesn't kill the motor now. it dims the dash panel a hair but that's it. any help is greatly appreciated!

 

[stonyloam]

14 volts while the engine is running is correct. The purple wire should be at battery voltage which should be about 14 volts when the engine is running the alternator is working correctly. The coil should be at reduced voltage due to the resistance wire in the circuit. You had a short to ground in there someplace with your purple wire. The purple wires should have battery voltage when the ignition switch is on, except for the coil end of the purple resistance wire. See if you can track down the spot where it shorted.

 

[Vipguy87]

ok. so I should have 14 volts at the key switch. Thanks! I completely replaced the purple wire because it was melted end to end. what could explain the key switch not working now?

 

[Scott Danforth]

The coil is fed by the resister wire (or balast resistor) because its a points ignition. You only get full battery voltage durring cranking

 

[stonyloam]

An internal short could have melted the contacts inside. Or if its short was somewhere else, just the massive current flow you saw could easily have burned the points. Probably a new switch is in order. You still have a potential problem that it could happen again. Get yourself a digital voltmeter and see if you still have a short somewhere. On ohms function go from the purple wire to ground to see if you still have a short.

 

[Vipguy87]

the coil reads about 6.5 volts when running. the purple wire going to the key switch from engine harness reads 14.5 volts when running. also key switch doesn't kill motor when turned off. just dims dash a bit. but motor continues to run.

 

[Vipguy87]

ok when I do that whay should the ohm reading be. and could this be causing my key switch not to function. I replaced the key switch when the original purple wire fried.

 

[stonyloam]

OK I Need to think a bit. Your purple wire goes From the switch to the harness, and on to the electric choke and resistance wire. So when your wire got hot the current was flowing from the switch to the harness and to a short to ground. Now voltage is feeding directly to the coil and it stays running. So disconnect the wire you installed to the harness, turn the switch on and see if you have voltage at the end of the wire, if you do turn off the switch, should go to 0 volts. If it does you have something backfeeding the ignition.

 

[Vipguy87]

so prior to installing the new purple from the harness to the key switch i started the boat and used my meter to test the piece of purple wire that I left sticking out of harness to splice to. it read about 14 volts. so power is definitely flowing from harness to key switch through the purple wire.

 

[GA_Boater]

I think you will find the insulation on the purple wire in the harness melted to another wire. You will have to make a jumper wire to bypass the shorted purple wire hidden inside the harness sheath. The dimming dash kinda tells you there is a short.

That can be checked by making up a long wire from the switch to the purple wire connection termination at the motor after disconnecting both ends of the purple wire. Then try turning the motor off. If it works OK, make the long jumper permanent.

 

[kenny nunez]

Look under the gunnal from front to rear, sometime a rub rail screw will penetrate the harness.

 

[Vipguy87]

thanks GA Boater! I'll check that out when I get home

 

[Vipguy87]

alright so jumper wired switch to purple wire on engine harness. no success key switch still didn't work. I began on taping all the wires running down from the coil to the engine harness and down to the alternator. I discovered that where the alternator wire the electric choke wire the resistance wire and the ignition wire all meet there was some serious corrosion and melted wires. So I cut the alternator wire loose from the other three started the boat and key switch works just fine. So the alternator was powering the ignition coil at all times even though the key switch was off. Man I hate electrical stuff. i rewired the purple wires and everything is fine. Thanks everyone for all your help you guys on here awesome