Ballast resistor question Mercruiser 4 cyl

[Fishermark]

I just purchased a Pertronix electronic ignition kit to upgrade from the points on my Mercruiser 4 cylinder. (1986 Sportcraft with 3.0 liter engine). The instructions say if the original system is equipped with a ballast resistor, not to remove it, but to install the red wire from the ignitor to the switch side of the resistor. Sounds easy, but I have a few questions:<br /><br />1) CAN I ASSUME I HAVE A RESISTOR? I assume I do. Here's what I have - I have two wires on the positive side of the coil. One wire leads to the starter, (giving it 12 volts at start I'm sure). The other wire has 12 volts when the key is on, and 4.5 volts when checked with the points closed. (I read in another post that the resistor will only "work" when current is flowing).<br /><br />2) WHERE IS THE RESISTOR PHYSICALLY LOCATED? I have a 56 Chevy, and the ballst resistor is a bulky unit located on the firewall. I see no such "unit" in the engine compartment of the boat. Is it somewhere else? Or is it a special "resistor wire"? If it is a wire, would it be in the harness on the engine itself? (In other words, after the big main plug harness at the back of the engine). I need to know because if it is, I guess I can just splice into the wire before the main plug harness, and be good to go.<br /><br />3) IS 4.5 VOLTS TOO LOW? I am wondering if that is sufficient voltage. I realize the voltage needs to drop, but that seems mighty low. Could the resistor be bad, and if so, does it need to be replaced? Or will this be a moot point when I change to the electronic ignition?<br /><br />I know that's a lot of questions.. but what can I say? I'm confused, , and you guys are the best "unconfusers" around! (Pertronix has a toll free number, but it isn't available till Monday morning).

 

[rodbolt]

Re: Ballast resistor question Mercruiser 4 cyl

hello<br /> you have a bad coil, bad points or a failed ground in the primary circuit<br /> points closed and everything clean and tight you should have a close to zero volt reading. with points closed you are checking the voltage drop acrossed a wire. your system uses a resistance wire. its the actual wire that feeds the + coil primary. your kinda right on the current thing. no current and there is no need for a resistance.<br /> points like 6.5 to 9.5 volts during sustaied operation. makes the contacts last longer. Points have been about forever and are still severly mis understood.<br /> the petronix is nice but really wont give any benifits on that motor if the points and related parts are kept in top shape. electronic will however tolerate more degrading than points. but I have never paddled or walked with points <br /> good luck and keep posting

 

[mati]

Re: Ballast resistor question Mercruiser 4 cyl

you may have an external resistor or the resistor maybe built into the ignition coil. When cranking the motor the ignition system is getting 12v. The moment the engine starts and release your switch to the on position the voltage gets kicked down by the resistor. If you continuosly run 12v into your points you'll burn up the contacts prematurly thats why the resistor and lower voltage.

 

[fireship1]

Re: Ballast resistor question Mercruiser 4 cyl

Hello, I have practically the same setup as you and I also have since converted it to electronic so I can speak from experience! Here goes!<br /><br /> Yes, you have a resistor in your ignition circuit. It is not the same resistor like the one in your car. It is a resistance wire. The resistance wire color is purple. It connects to the alternator output wire a little after the large cannon plug at the back of the engine. The alt output wire is also purple. You will see 12 vdc when the key is on and you probe this wire. The resistor wire is not a great setup. I had problems with mine changing voltages as the wire heated up. It drove me crazy because the engine would run great for about an hour and quit. The wire was changing resistance and letting the coil overheat. Then the motor would quit! You could change the resistor wire or just add a ballast resistor from auto supply. The Pertronix system is made to use the original coil and resistor setup. If you keep the stock coil you need to use some kind of resistor or you will overheat the coil. I would do this instead, Ditch the original coil and pick up a flame thrower coil from pertronix. Or get a 12 volt universal coil with brass terminals (so they don't rust) Find the purple wire where the resistor wire connects (remember they junction right near the cannon plug) and clip the resistance wire there. Tap that spot for switched 12 volts and hook up that to the positive side of the coil. Hook up your pertronix ignitor wires to pos and neg of the coil and install the ignitor in the distributor and you will be all set. No more resistance wire and fickle Mercruiser stock coil. The pertronix likes straight 12 volts as opposed to the 6 to 9 you will find at the end of a resistance wire. You will eliminate a bunch of Gremlins doing it this way! Good luck!

 

[Fishermark]

Re: Ballast resistor question Mercruiser 4 cyl

Thanks all,<br />Fireship - that's pretty much what I've decided to do I believe - go the internally resisted coil route and bypass the resistor wire. I'll keep you posted!

 

[rloucks3]

I have a 120 horse with a balast resistor and electronic ignition I only seem to get 8.8 volts cranking and 12 volts not cranking.