burning points...D17

Try a different coil. Measure across the coil terminals and see if you have about 3 ohms. Some coils say "12 volts with resistor." It's a clever way of disguising what's really a 6 volt coil.



Edited by DougS - 16 Sep 2019 at 6:56pm

12 volt systems on automotive run on 6 volts for points but 12 volts to start. To do that an external resistor is used or resistor wire(GM cars). But they start on 12 volts so you have wire from solenoid to accomplish that. So two wires on positive side of coil. The 12 volts is only when starter is cranking. Is your system positive or negative ground?

Edited by Ed (Ont) - 16 Sep 2019 at 8:54pm

What series D17 is it?        MACK

I bought a WD45 that was real hard on points. Had a 12 volt coil on its aid so right on the coil. Eventually I gave up and pulled the coil put a new on on. When I wiped the dirt of that was under the mounting band in small print it said external resistor required. My Corvette has one of those coils on it when you start it 12 volts goes from the starter solenoid to the coil. When you release the start switch. Power comes from the ingnition switch thru a ballast resistor to the coil. If you get the coil from a 57 Chevy that's what your going to get.

That D17 should've had the same setup as the old Chevy's & Mopars had like the guys mentioned. The only difference between the two was GM used a resistor wire that ran in the harness, where Mopar ran the external ballast resistor on the firewall. I saved many damsels in distress at the local supermarket back in the sixties on rainy days cause there Duster or Scamp wouldn't start! When in the crank mode, 12V's is supplied to the coil till the key is let go. Once out of the crank mode, and into ignition mode, current then ran through a ballast resistor to the points. I have an original D17 harness that I use for a pattern to build my new harnesses from, and that has a ballast resistor in the OEM wiring system. It sounds like the Ballast resistor was removed at sometime and that's why you don't get any longevity out of the points JC. What I would do is pick yourself up a new coil (12V/3.0 ohm) with a built-in resistor. This way Mother Nature can't play havoc with the external resistor (like it did in the old Mopars) toss a real set of points and condenser in it like the SMP Blue Streak brand, and let r' rip!  We have all of that in stock if interested, or you can go locally and find a Blue Streak dealer to get everything ya need.  HTH    BTW, Ed thanks for the mention....! Its appreciated!

My '68 gas 4020 had the resistance wire in the harness going to the coil and an extra contact on the starter solenoid to supply full battery voltage to the coil while cranking. The resistance wire went bad and somebody replaced it with a fixed ballast resistor and the wiring near the ignition switch went bad. When fixed it started fine and worked all day on the coil without overheating it.

Gerald J.

Dave is correct. If you're going to change to Neg. Grd., you want a Neg Grd E.I.  Make sure you run resistor/carbon core spark plug wires also when using an E.I.  Solid core wires could spike the electronic module and take it right out. Also to, when charging the Battery in the Tractor, disconnect one cable (doesn't matter which one) before you charge the Battery. Just eliminates possibly blowning the module out while in charge or boost mode. I've had customer's jump up on their Tractors to fire em' up only to have a dead Battery. They hop off and would forget to shut the key off, grab their Battery booster and put a super boost into the Battery only to take out the E.I. along with it cause' the key was left on. That's another way how to throw a little over 100 bucks out the window. E.I.'s are great. You just need to be careful and not forgetful to keep em' in service. We keep all the different E.I.'s in stock if interested.....

It will work fine with a coil with an internal resistor, JC. Of course you'll want to keep the tractor tuned up with good plugs and wires in addition to the points, condenser, rotor and distributor cap. This would be true for any gasoline tractor, with or without a 12 volt internally ballasted coil. BTW, it would cost very little to switch to negative ground if you have a generator. No need to change to an alternator. Your biggest expense might be to buy new battery cables with the properly sized positive and negative terminals.

Most old regulators I've seem were labeled "A" "F" and "BAT". Occasionally I've seen a fourth terminal that goes to the light switch. I've not seen a polarity marking unless your regulator happens to have been upgraded to a solid state job. If you have it working now the way yo want, leave good enough alone. Beware of getting water on that resistor when it's hot. I mean they get very hot. A splash of cold water on a hot component may cause it to crack.