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post #1 of 16 Old 02-10-2019, 06:19 PM Thread Starter
jlkeener
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Alternator question

Can anyone advise if I should have voltage on the wire going to the #1 terminal of a Delco SI alternator. My alt quit charging and upon checking the two wire plug a get 12 volts at #2 terminal all the time key on or off. I get no voltage at #1 terminal with key on or off. I'm thinking I should have 12 volts at the #1 terminal with the key on. Someone Please enlighten me!!

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post #2 of 16 Old 02-10-2019, 07:25 PM
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You are correct. #1 should hot with key in on position

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post #3 of 16 Old 02-10-2019, 10:09 PM
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That *MAY* be a resistor wire, so unplug it and check for voltage... Mine was a resistor wire, but it is an aftermarket harness, but usually aftermarket tries to copy OEM on that kind of stuff.

Rick

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post #4 of 16 Old 02-10-2019, 10:23 PM
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Won’t matter regarding resister wire. Will show voltage with key on and hooked up, if functional. Won’t be batt voltage level, but will have voltage, if circuit functional.

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post #5 of 16 Old 02-11-2019, 09:34 AM
JohnnyRotten
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Do you have a Painless wiring harness? If so check the wiper fuse. That is the circuit that "excites" the alternator.
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post #6 of 16 Old 02-11-2019, 12:05 PM Thread Starter
jlkeener
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thanks everyone, that's what I thought. It is a stock wiring harness and its a brown wire which I believe should be a resister wire. Ill break open the harness and try to track down the source.
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post #7 of 16 Old 02-11-2019, 12:10 PM
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Bulkhead connector good place to look

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post #8 of 16 Old 02-12-2019, 12:07 PM Thread Starter
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Yes that's where it went pin 79 I believe. Not sure where it goes from there on the inside.
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post #9 of 16 Old 02-12-2019, 01:13 PM
John Strenk
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Quote:
Originally Posted by jlkeener View Post
Yes that's where it went pin 79 I believe. Not sure where it goes from there on the inside.
It goes to the ignition switch and the always hot side of the fuse box.


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post #10 of 16 Old 02-15-2019, 01:24 PM
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What issues would be caused by having less than 15 ohms (as shown in 1980 FSM schematics) going to pin 1 on a 10SI type alternator? Would battery charging be effected? Would I potentially damage the alternator? I’m talking resistance of around 10 or 12 ohms, I forget the exact number.
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post #11 of 16 Old 02-16-2019, 09:46 AM Thread Starter
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Not sure on what the ohms should be, but I know you need a resistance wire or a diode on that wire to keep the alternator from back feeding, which would prevent you from being able to shut off the engine with the key switch.
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post #12 of 16 Old 02-16-2019, 10:22 AM
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Quote:
Originally Posted by trailhead2004 View Post
What issues would be caused by having less than 15 ohms (as shown in 1980 FSM schematics) going to pin 1 on a 10SI type alternator? Would battery charging be effected? Would I potentially damage the alternator? I’m talking resistance of around 10 or 12 ohms, I forget the exact number.
Contrary to what is often said, the resistor wires MAIN purpose is for the sake of the alternators voltage regulator. It only comes into play with the key on engine off situation. Terminal #1's circuit also goes through the slip rings and rotor windings. Without a resistor of some type, there would be a fair amount of current flowing through that. With engine running it doesn't matter much, or at all. Many people have ignored the resistor wire and hooked up terminal #1 with no resistor of any type and run that way for years with no ill effects, so they claim. I suppose it's a mute point if they don't sit there with the ignition key on for a long time with the engine off.

Alot of people claim the resistor wire is there to prevent back-feeding to the vehicles electrical system causing run on, after the ignition key is turned off. That is true. AMC and other manufactures, in their infinite wisdom, spliced the alt excite wire in with ignition system wiring. Yes, the resistor wires purpose is ALSO to drop voltage down below what the ignition coil needs to fire the plugs after the ignition key is turned off. It's a dual purpose resistor wire. It's a two fer. A diode can be used, and is often times added by owners, to achieve a more guaranteed result.

You never want terminal #1 hooked to the "hot at all times" side of the ignition switch because it will sit there and slowly drain the battery when the rig is sitting.
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post #13 of 16 Old 02-16-2019, 12:20 PM
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Quote:
Originally Posted by jlkeener View Post
Not sure on what the ohms should be, but I know you need a resistance wire or a diode on that wire to keep the alternator from back feeding, which would prevent you from being able to shut off the engine with the key switch.
Yeah, I've even read in a few places that you can run without it, not sure about that though. I think I'm leaning toward an idiot light in the long term. I was reading through some older posts last night where JEEPHAMMER was talking about some cool things to do with a single idiot light for monitoring charging, oil pressure, and engine temperature. I'm not going to dive into my CJ5 and change that stuff since it's already back together, but I'm certainly considering it for my CJ7.

Thanks for the input jlkeener!
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post #14 of 16 Old 02-16-2019, 12:22 PM
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Quote:
Originally Posted by TIPPEDITOVER View Post
Contrary to what is often said, the resistor wires MAIN purpose is for the sake of the alternators voltage regulator. It only comes into play with the key on engine off situation. Terminal #1's circuit also goes through the slip rings and rotor windings. Without a resistor of some type, there would be a fair amount of current flowing through that. With engine running it doesn't matter much, or at all. Many people have ignored the resistor wire and hooked up terminal #1 with no resistor of any type and run that way for years with no ill effects, so they claim. I suppose it's a mute point if they don't sit there with the ignition key on for a long time with the engine off.

Alot of people claim the resistor wire is there to prevent back-feeding to the vehicles electrical system causing run on, after the ignition key is turned off. That is true. AMC and other manufactures, in their infinite wisdom, spliced the alt excite wire in with ignition system wiring. Yes, the resistor wires purpose is ALSO to drop voltage down below what the ignition coil needs to fire the plugs after the ignition key is turned off. It's a dual purpose resistor wire. It's a two fer. A diode can be used, and is often times added by owners, to achieve a more guaranteed result.

You never want terminal #1 hooked to the "hot at all times" side of the ignition switch because it will sit there and slowly drain the battery when the rig is sitting.
Understood. Thanks TIPPED!
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post #15 of 16 Old 02-17-2019, 07:58 AM
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Quote:
Originally Posted by trailhead2004 View Post
Yeah, I've even read in a few places that you can run without it, not sure about that though. I think I'm leaning toward an idiot light in the long term. I was reading through some older posts last night where JEEPHAMMER was talking about some cool things to do with a single idiot light for monitoring charging, oil pressure, and engine temperature. I'm not going to dive into my CJ5 and change that stuff since it's already back together, but I'm certainly considering it for my CJ7.

Thanks for the input jlkeener!

One thing to keep in mind - if you install a light in the wire, run a separate non-resistor wire, as the bulb + resistor wire will drop voltage a lot. Also, use a resistor across the bulb socket connections so that when the bulb blows out, the alternator will still charge. Someone here may have the resistor value to use, or you can Google it. It has to be higher than the bulb...

Rick

1978 CJ5 5.0HO/T177/D300, '86 D30/D44 WT axles, 'glass body, 31x10.5 BFG A/T, TDK galv'd frame - DD and weekend toy


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