Ignition Coil Problem

T

tinytanic1

Cadet
Joined
Aug 7, 2007
Messages
13
While my 16ft runabout is running the ignition coil gets so hot you can't even touch it. Then if you shut off the engine, it won't start again. I've replace coil, distributor cap, points, plug wires, and the external resistor wire that connects to positive side of coil. Sometimes, I have a full 12 volts at the coil, other times I only have 6 volts. I should have a reduced voltage at coil due to resistor wire I think? This is 1977 Mercruiser 120hp (2.5L) with 4 cylinders. HELP! I've run out of ideas!
 
wire2

wire2

Lieutenant Commander
Joined
Jun 25, 2007
Messages
1,584
Re: Ignition Coil Problem

You're on the right track. The coil is supposed to get a full 12 volts through the start solenoid circuit, then drop off to 6-7 volts through the resistor for running. If it stays at 12, it will heat the coil. It sounds like a wiring fault to me, as if the resistor is being bypassed through a short. Trace the + line backwards from the coil to see where it comes from.
 
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