Mercruiser 165 ballast resistor?

auscarter12

Seaman
Joined
Jun 19, 2015
Messages
59
Took my 1971 Aristocraft to the shop to seek out an ignition issue. Found out the ignition coil was bad (only 1 year old). It has a Mercruiser 165 straight 6 engine. My question is this: does this motor use a ballast resistor for the ignition coil? If so, where should it be located? I'm thinking maybe mine doesn't have one and that is why the coil went out prematurely.
 

thumpar

Admiral
Joined
Jun 21, 2007
Messages
6,138
It should either have a ballast resistor or wire. If it is the wire type the wire is the actual resistor.
 

auscarter12

Seaman
Joined
Jun 19, 2015
Messages
59
It should either have a ballast resistor or wire. If it is the wire type the wire is the actual resistor.

I'm not very good with electrical work. How would I know if it had a resistance wire? Where would it run from and to? Is it a thicker gage or a different material? Also, if I added a ballast resistor, is there a certain resistance rating needed for this model?
 

GA_Boater

Honorary Moderator Emeritus
Joined
May 24, 2011
Messages
49,038
The resistance wire is between the run position on the ignition switch and + on the coil. The resistance wire is bypassed to supply full battery voltage to the coil for a hotter spark when cranking the motor over since using the starter usually drops the voltage. After the motor starts and the key is released, the resistance wire drops the coil voltage to roughly 6 volts because the hot spark isn't needed then.

Not saying BT's idea of an internal resistor coil isn't good, a simpler circuit and longer coil life, but if your motor isn't in good tune the weaker spark may make for harder starting. If you can't find the resistance wire or it's bad, use an internal resistor coil.

Not the best pic below - The resistance wire is white.
165reswire.PNG
 

achris

More fish than mountain goat
Joined
May 19, 2004
Messages
27,468
The resistance wire looks just like any other wire. You need a GOOD QUALITY digital multimeter to find it (something like a Fluke73). It's in the engine harness, between the main 10 pin Canon plug and the + side of the coil.

If it's faulty you can either replace the resistance wire with normal wire and an external ballast resistor or a new resistance wire from Mercury, part number 84-94227A2, still available. I would not put an internally ballasted coil in for the reasons GA pointed out. The voltage drop from the battery during cranking will reduce the spark power just when you need it most....

Chris......
 
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