Need help wiring points on a 77 140

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Need help wiring points on a 77 140

Postby David C » Mon Jan 07, 2013 11:34 pm

Hey guys I could use some in depth help repairing a botched rewire on my 140 I just got. It has a "made in china" key switch. and an original alternator with a resistor mounted to the back of it.

My problem is it doesn't utilize the resistor like it supposed to.as seen in the picture, the bottom of the resistor(2 wires) has power coming from the key switch and then goes to ign coil. it has a FULL 12 + volts all the time thus making the coil get very warm/hot! Isuspect it is missing a wire and or the correct key switch...can y'all help me out as I cant find a correct diagram and switch...
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Re: Need help wiring points on a 77 140

Postby Jim Becker » Tue Jan 08, 2013 12:25 am

I don't have a wiring diagram for that versio of a 140. The Case-IH parts site is down right now, so can't look there either. So this is all just a hunch, need other verification.

I suspect the original ignition coil was a 12-volt no-ballast-required coil. The ballast resistor on the back of the alternator is not for the ignition but rather to feed the excitor terminal of the alternator. If so, the "I" terminal of the ignition switch should be directly connected to one end of the resistor and the coil. That is what you have. The other end of the resistor should go to the excitor terminal of the alternator. The other small terminal of the alternator should have a sense wire, which may be what the other wire there is. I am unsure about whether terminal 1 or 2 is the excitor. Maybe the 2 wires are backwards on the alternator.
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Re: Need help wiring points on a 77 140

Postby Eugene » Tue Jan 08, 2013 5:23 am

Disconnect tractor battery. See if the the wire plug at terminals marked 1 & 2 will fit if turned around.

Have a wiring diagram for Delco dated 1968. Diagram shows the resistor, an indicator (dash) light, and the ignition switch connected to terminal 1. Terminal #1 is the exciter terminal.

Terminal 2 is battery voltage, connected directly (or indirectly, not switched) to the positive terminal on the battery.
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Re: Need help wiring points on a 77 140

Postby Gary Dotson » Tue Jan 08, 2013 8:10 am

As the alternator is connected in the photo, it is correct. Number 1 terminal is indeed the exciter terminal, as Eugene mentioned, hence the resister connected to it. As Jim mentioned, the resister is not for the ignition system, it should have an internal resister coil with no need for a resister. If your coil is overheating, it's probably an improper coil. One little tip, though, check your point gap. If the point gap is considerably closer than spec, it can cause the coil to run warmer than it should.
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Re: Need help wiring points on a 77 140

Postby Jim Becker » Tue Jan 08, 2013 8:13 am

Gary Dotson wrote:As the alternator is connected in the photo, it is correct. Number 1 terminal is indeed the exciter terminal, as Eugene mentioned, hence the resister connected to it.

Looks to me like the resistor is connected to #2 in the picture???
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Re: Need help wiring points on a 77 140

Postby Eugene » Tue Jan 08, 2013 8:24 am

Yup what Jim said.

Another check. Engine off. Disconnect the plug. Multimeter, 20 volts DC, check voltage from terminals in the plug to ground. The plug terminal going to terminal #2 on the alternator will be 12 volts. Plug terminal going to alternator terminal #1 will have zero voltage with the ignition switch off.

Edit: http://s101.beta.photobucket.com/user/f ... sort=4&o=3

Above wiring diagram is only to show the terminal locations on the back of the alternator. Not intended to show the tractor's wiring. Also, the Delco 10SI in the above wiring diagram is not the alternator on the tractor.

Nother edit: Simple solution would be to replace the alternator with a single wire Delco, or Delco clone.

And another edit: Guessing the alternator is 20 to 25 years old. I would replace it.
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Re: Need help wiring points on a 77 140

Postby Gary Dotson » Tue Jan 08, 2013 9:55 am

I'm sorry guys, I mixed up my 1s & 2s! #1 is voltage sense and #2 is excite. At any rate, it's still correct in the pic.
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Re: Need help wiring points on a 77 140

Postby Matt Kirsch » Tue Jan 08, 2013 11:15 am

Here's the $1,000,000 question: Is it charging the battery?

If yes, then all you need's the right coil and you'll be fine.
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Re: Need help wiring points on a 77 140

Postby David C » Tue Jan 08, 2013 12:09 pm

Sorry guys i have very limited access to the net at work and yes it does charge the alternator...

Thanks to all you guys for setting me straight. I was having a time figuring what that resistor is for and why the previous owner had a bad coil on it.
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Re: Need help wiring points on a 77 140

Postby Eugene » Tue Jan 08, 2013 12:25 pm

Joe Guilbeau's Alternator Theory Page. Section 2…”Delco 10-SI and Delco 12-SI Alternators.

Here are the details on the individual terminals:

"Bat"- this terminal is for the alternator output to the battery.

"1"- this terminal (usually closest to the "Bat-terminal") is fed from the Ignition thru a lamp ("idiot light"), and is used to supply the magnetic field inside the alternator with the voltage needed to operate.

"2"- this terminal can be fed from the positive battery post. This is an input to the alternator that is used to sense the battery voltage
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Re: Need help wiring points on a 77 140

Postby Eugene » Tue Jan 08, 2013 3:16 pm

David C wrote:I was having a time figuring what that resistor is for and why the previous owner had a bad coil on it.
Wetzel, Automotive Diagnosis and Tune Up, 1974. "In other circuits, the lamp is in series with the field and in parallel with a resistor. Current through the lamp and parallel to the resistor is used to initially energize the field on the alternator so it can produce." This circuit to the alternator is controlled by the ignition switch. Depending on how the tractor is wired, the circuit exciting the alternator, may or may not have a lamp (idiot light). Wetzel's text book was written for automotive courses.

Matt Kirsch wrote:Is it charging the battery? If yes, then all you need's the right coil and you'll be fine.
Not so. Take a look at the wiring diagram cited in my second post on this topic.
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Re: Need help wiring points on a 77 140

Postby Jim Becker » Tue Jan 08, 2013 4:48 pm

Still looks to me like the wires on 1 and 2 are backwards. Thinking just very briefly about the expected effect of that. I think it would charge normally (or very close) but probably cause a battery drain whenever it isn't running. Has the battery been staying charged?
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Re: Need help wiring points on a 77 140

Postby David C » Tue Jan 08, 2013 6:43 pm

Jim Becker wrote:Still looks to me like the wires on 1 and 2 are backwards. Thinking just very briefly about the expected effect of that. I think it would charge normally (or very close) but probably cause a battery drain whenever it isn't running. Has the battery been staying charged?

Thanks Guys, As far as "does the battery stay up", I dont know yet as the battery was VERY old and bad. Just replaced the battery this week.

I am gonna take my new, unused coil back to the parts house and get a coil the doesnt require the resistor.I will let you know if the new battery runs down.

I cant thank you all enough for the help! Once again Farmallcub.com comes to the rescue!!!

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Re: Need help wiring points on a 77 140

Postby Eugene » Tue Jan 08, 2013 6:54 pm

Eugene wrote:Another check. Engine off. Disconnect the plug. Multimeter, 20 volts DC, check voltage from terminals in the plug to ground. The plug terminal going to terminal #2 on the alternator will be 12 volts. Plug terminal going to alternator terminal #1 will have zero voltage with the ignition switch off.
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Re: Need help wiring points on a 77 140

Postby David C » Tue Jan 08, 2013 6:58 pm

Thanks I will check it

David C
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Tractors Owned: 1949 Farmall Cub, 1970 135 Massey Ferguson, 1970 175 Massey Ferguson, 1964 Cub Cadet Model 70. 1977 Farmall 140 (Granpa's)

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