1979 MERCRUISER 140

[electricamp]

Hello, I have an electrical problem. I run the boat for 30 min, and the boat shuts down, won't wont start until it cools off. During this time, the COIL is REALLY REALLY hot. I had a guy swap the wiring and everything to the coil and change the COIL and still no luck. What direction should i be looking in now?

[daveswaves]

Hi, the most likely problem is that your coil is wired backwards, that is the the Plus terminal is connected to ground and the minus terminal is connected to power. The coil will overheat and cut out, then when it cools down the whole thing will start over again. The wiring should go from the inition (bat) to the + of the coil. The neg of the coil should go to the distributor (points). The points then ground the coil when they close. You may have cooked the coil.

[electricamp]

I just had a mechanic rewire it. We had recently put electronic ignition in and got rid of the points. What else could be wrong?

[DJ]

elictricamp,You may also be running 12 volts to the coil. It should only get about 9.5 through a ballast resistor.

[Yepblaze]

Sounds like the coil is overheating. It may require a resistive wire feeding the coil. Standard and pointless coversions. Need either to have a resister before the coil or a coil with an internal resistor. You will have to make sure you have one or the other. So if you see full battery voltage to the plus side of coil, you should make sure the coil is of internal resistor variety.

[electricamp]

so If i get a full 12v at the coil and i have an Internal Resistor coil, that is bad? thanks

[daveswaves]

You do not say whether everything ran fine after the switchover or if this is a new problem. I know the mechanic re did it all, however, its easy to mix up the wires. The guys are right on with the voltage, if you have 12V at the coil term then you better have an internal resistor coil. If you dont have an internal resistor coil then you will have to install an external resistor. I know you no longer have points, however the electronic "box" you installed is doing the same thing as the points, too much voltage or incorrect polarity will heat up the coil and it will cut out.

[Trent]

Check this link out and maybe it will help??? web page

[electricamp]

After the Mechanic installed the new coil and wiring, it ran the exact same as before. Runs great for about 30 min, then it shutsdown, and the coil is real hot. Would it run in the first place if the wires were backwards? thanks

[daveswaves]

Hi electricamp, yes the engine would still run with the coil reversed, the coil just heats up and quits because the polarity is wrong. There is a possibility that your old coil was wired wrong and the mechanic simply copied what was there. If he is not familiar with boat wiring etc. he may have "played it safe" and just moved wire for wire. Should be easy to check, the coil terminal should either be marked with a + or a "bat" marking. the other term will be - or gnd.