internal or external resistor in coil?

I forgot to add resistor, internal or external does it matter?

If you have a resistor in line you do not need a resistor coil, and you do not need resistor plugs that I am aware of, someone else will know for sure but i think i am right

most are a porcelin box that will be on the hot side of the coil were the power comes in to the coil

All 12v systems need a resistor.  If not the voltages are to high and will burn the coil up.  If you have a 6 volt coil, you need to add a balast resistor, available from NAPA.  If you have a coil labeled for 12v use it will have a resistor built into the coil itself.

Resistor spark plugs or resistor plug wires have nothing to do with a tractor, their more for radio interference suppression on autos. 

If you switched to a 12volt negative ground then it should go from the switch, to the positive coil terminal, then from the negative coil terminal to the distributor

How do you know if it is neg or pos ground system.  I am no good with electrical stuff.

If there is no external resister then use a multimeter to check the resistance(ohms) as shown earlier.

a negative ground system will have the negative post cable go to ground(the tractor frame)  and the positive cable will go to the starter.

A positive ground system should be the oppisite, but most 12v systems are negative


Edited by firebrick43 - 12 Feb 2010 at 10:27pm

Weren't all D17's already 12V? Are you converting from generator to alternator?

Not sure what you have there, but, not all 12V systems use a resistor. The GM HEI is one system that does not. When it comes to coils, I always try to persuade my customers to run a coil with an internal resistor. Main reason why is Mother Nature plays havoc with external resistors with moisture. External resistors cause engine misses, hard starting, and other running issues. The external resistors didn't work under the hood of 60's automobiles, (especially on rainy days) they sure as heck don't work well hanging out in the elements on a Tractor. Your system should have been 12V Positive Ground with Generator accompanied by an external Voltage regulator. If you're upgrading to an Alternator, you'll want to change over to Negative ground, and use the simple "SI" series Alternator to do the charging chores. This has a built-in regulator, so the external regulator can be put aside or disgarded. The D17's wiring will suffice for a 12V conversion providing its in GOOD condition. In the "D" series wiring systems in general, AC used a "stacking" method of utilizing mulitple circuits off of the same Ignition terminal. It worked, but as the systems aged, the stacking causes more resistance in certain area's of those systems, as well as the light load Ignition switches that were used, and electrical failures were not uncommon either downstream or at the Ignition switch. If a new wiring system is out of your budget, make sure the OEM wiring is in good shape first, and replace anything that doesn't look good or has the wire jacket cracking or peeling off from age. I offer an upgraded Ignition switch which incorporates a plug rather than a pile of female connectors which are used to "stack" circuitry. This plug design eliminates the stacking, and makes a much cleaner and better operating wiring system at the back of the dash panel where it can get like spaghetti.  Hence, the problems that occured over the years with the "D" series wiring. If you would like some help in figuring out which way to go, just give me a call. Be happy to help you out as I did with a lot of the forum members over the years here. Wiring information and guidance doesn't cost you a dime....
Steve@B&B        (973) 632-5596 

I rewired the tractor with new wire, The old wire was all cracked and corroded,it is 12 volt neg ground with altinator. The volt reg i took off tractor, I used plastic flex tubing to act like harness for all wires and tie strapped them up. My coil, on the inside is cracked and does not give good contact, (after many years of being out in the adverse weather)  so its time for a new one. Good Idea on the switch, keeps ends from touching or arcing I imagine.