656 Ignition Coil Voltage

I have a 1970 656 that uses a resistor wire to the coil. Reading at the coil is 8v. It starts hard in colder weather. Engine pops once or twice and then crank, crank, crank. As an experiment, I ran a jumper 12v wire to the coil. Pushed the starter button and it popped right off. I'm thinking about installing a momentary "on" toggle switch with 12v to be used momentarily during starting only. Do any of you electrical gurus see a problem with that?

Thanks in advance for your response.

Most are wired at the starter solenoid to by pass the resistor for starting.

I'm surprised your 656 isn't already wired like that. Most vehicles when they went from 6 volt to 12, kept the 6 volt coil just for that purpose. When you hit the starter button, the resistor was bypassed and 12 volts went to the coil, as soon as you released, it went back to 6 thru the resistor. Your reasoning is spot on!

Look at the solenoid and if it has 1 big wire which is the battery cable and 2 small wires it should already be wired that way but just because it is wired that way does not mean it is still working like it should be. 1 small wire is the start circuit and the other small wire if it has 2 is the resister by pass wire

Here's the info straight from the IH GSS-1310 "Electrical" Blue Ribbon Service Manual...

Ignition resistor bypass wire connects from ignition switch side of coil primary to "R"(esistance) terminal on starter solenoid.

<img src = "http://oi67.tinypic.com/o05her.jpg">

Thank-you all for the replies. Bob, your diagram shows a ceramic style resistor and two wires on the + side of the coil. I fully understand the starting concept. I don't have the ceramic style resistor and only 1 wire at the + side of the coil. I believe this single wire to be a resistance style wire reducing 12v down to 8v. Where am I going wrong?

The resistance wire and the ceramic resistor can be used interchangeably. If there's an small terminal marked "R" on your starter solenoid, simply run a wire from there to the ignition switch side of the coil primary.

(Typically Delco marked the starting bypass terminal on the starter solenoid with an "R", Ford and likely some others label it the "I" terminal.)

Bob, I know what you're saying and thought about running the extra wire from the solenoid to the coil as you suggest. But, if I do that the extra wire will get a back feed of 8v from the coil to the solenoid. I'm concerned the 8v might engage the solenoid. If this makes no sense, I'll try to reword.

As Bob said if you have the R terminal hook that to the coil and NO it will not back feed since it only has power on it when the solenoid has power to spin the starter.

I or R terminal has no internal connection to the solenoid activating coil. That terminal is completely disconnected internally until the solenoid is activated.

A late mode 656 will have a resistance wire instead of the white ballast resistor. However, the resistance wire is in the wiring harness between the starter solenoid and a junction block under dash and from junction block will be plain wire to ignition switch. Easy to tell by looking at the wires going to wires at starter solenoid. If the ignition terminal on the solenoid has two wires hooked together , it has resistance wire in harness. You will see about 5 or six volts at that terminal with engine not running , switch on and points closed drawing current. When you hit the starter you should see battery cranking voltage at that terminal as well as at in put side of coil terminal which should be about 11 volts. If you do not see increased voltage when cranking the internal contact is not making connections to that terminal feeler inside solenoid. You should definitely not hat an added resistor be it ballast resistor or resistor wire from starter solenoid to ign coil and you should have a 6 volt coil marked for use with external resistor. That wiring diagram shown is for an early 656 and I don't think IH ever published one for the later models. Just bulletins or letters.

Thanks Pete. I do have 2 wires going to the same terminal on the solenoid. So, resistance wire. I'll check the voltage there tomorrow. I understand that when cranking the voltage at that terminal should be around 11v and if not, not making contact internally in the solenoid. P/n for that solenoid is 1114356 and available about everywhere.

I would pull both the small wire off the solenoid and then turn the key to the start position and see which wire has power and which one does not. I'll almost bet the one with out power should be on the I or R terminal that is not use at this time and is the ballast resister bypass wire

According to the page from the IH manual, which is also true of most tractors with resistor/coil setups, you should see 6 volts at input to coil with switch on, points closed. The resistance across coil primary should be 1 1/2 ohms and resistor should be 1 1/2 ohms.

If you have 8 volts at the coil I would suspect that you have too much resistance between ignition switch and input to coil. Possibilities are a defective resistance wire, someone has added another resistor in series with the wire, or someone used an alternator conversion kit that came with a resistor that had too much resistance.

Specs in a book often look good but they over simplify what you actually will read. After all the years I have spent checking voltages at various sources you learn what is acceptable and what is not. I have never seen any voltage reading at a coil that was exactly six volts after coming through a resistance wire or ballast as just the temperature of the resistor and the coil make for different readings let alone the condition of the entire wiring system.

?Specs in a book often look good but they over simplify what you actually will read.........?

I agree 100%. Voltage readings given in most old manuals are nominal or ?ball park? readings and not intended to be minutely specific.

I always assume that ?6 volt? and ?12 volt? are approximate and not specific. A full charged ?6 volt? battery is around 6.3 volts and a full charged ?12 volt? around 12.65. When being charged by generator or alternator I would expect them to read approximately 15% above that.

I spent about 35 years in radio and tv service. Back in the tube and early transistor days ?real world? voltages within + or ? 10% of that given in the manual were often considered to be within tolerance. I would consider the same to be true in the old tractor world.

When vcr, microwaves, and other computer controlled devices came along it was a different world entirely, as some of those circuits had to be within as little as a few hundredths of a volt of the reading given in the manual. That discussion is beyond the scope of this time and place.

When the original post for this topic stated that there was 8 volts rather than 6 at the junction of coil and resistor I consider that to be out of normal tolerance and worthy of troubleshooting to find out why.

In looking at the original post, I would bet he got the 8 volts at the coil when the engine was running and alternator charging and then that would be normal for all I have checked. I would guess he would have more like 5 volts when not running. Other wise, all bets are off.

You mention microwaves, hey, I just ordered a micro switch for ours as door switch broke. Not my usual repair item though.

Oh, yes, micro switches on microwaves. It will be just like some parts on a tractor, not hard to replace.......once you can get to it!