12V replacement coil for 1971 Mercruiser 165

[Howard Sterndrive]

I have a 1970 or 71 Mercruiser 165 here. It has the 2 ceramic heater type ballast resistors in series. They are a mess... brittle wires, corroded nuts on the back.
I want to ditch them and find a nice 12V coil that I can just run the ign wire to @ 12V. Will that affect the points?
Suggestions?
One that would fit in the stock barrel type clamp would rock.

 

[6meter]

Re: 12V replacement coil for 1971 Mercruiser 165

You can't put 12v to points for very long before they burn up. Thats why there was a resistor block or resistor wire in all point dizzy engines. You want 9v on the coil.

 

[essveedub]

Re: 12V replacement coil for 1971 Mercruiser 165

I upgraded my coil on my '76 Mercruiser 140 to a 3.0 ohm internally resisted coil. I was able to bypass the resistor wire in my setup and run straight 12V to the coil. However, I also put in an electronic ignition kit at the same time, so I don't know how removing the ballast resistor would affect points/condensor. From what I've found the resistors protect the coil from overheating, so I'm assuming the points may not matter?

Info I got mentioned that you could run the 3.0 ohm coil on 4 & 6 cyl.

 

[Howard Sterndrive]

Re: 12V replacement coil for 1971 Mercruiser 165

I thought the resistor protected the coil, not the points so much...

I wonder if there is an electronic ballast resistor or good aftermarket plate mounted resistive unit.
kinda freaks me out having this heater coil in the engine compartment.

 

[dbkerley]

Re: 12V replacement coil for 1971 Mercruiser 165

I bought a stock 12v externally resisted coil for a '74 chevy pick up and added a ballast resistor to get the ohms right for a 6cyl and then put the pertronix unit in. I think the required resistance for a 6-cyl is over 3 ohms across the coil.

The resistor is for the coil and not the points. The resistance requirements also vary from 4-6-8 cylinder engines. I ran it without the resistor for quite awhile on the points and didn't burn them up any faster than otherwise.

 

[Silvertip]

Re: 12V replacement coil for 1971 Mercruiser 165

It is not a heater. It is a resistor and it is wire wound. Ballast resistors have resided in the engine bays of cars and trucks for decades and later as a piece of resistance wire built into the wire harness. Replace the dual units with a single of the same combined resistance and go boating.

 

[windsors03cobra]

Re: 12V replacement coil for 1971 Mercruiser 165

My boat had no ballast resistor and had a coil for use with an external one. well that coil got flaky on me tone time. Last ride it took.

Went to Napa and a coil for use without external resistor. Been running like that for almost 2 seasons now with the same set of points. Starts great.

 

[achris]

Re: 12V replacement coil for 1971 Mercruiser 165

There are 2 different coils commonly available. One for use with an external resistor and the other that can be fed raw 12volts.

The reason for a 7 volt coil and an external resistor is to allow a bypass feed of the full battery voltage during crank of the engine, when the available voltage is lower than 12 volts (due to the load of the starter motor). Use a 12volt coil (internal resistor) and during cranking you will have a weaker spark, especially if the battery is a little low.

Chris......