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I have a new alternator to put into my mj - as soon as the weather warms up a bit.  But I need a bit of insight into how the alternator hooks up to the wiring.  This could be a stupid question, but here goes:

The wiring diagram shows three wires connecting to the alternator.  Looks like they go to battery, ignition, and instrument cluster.

My jeep only has two wires actually connected at the alternator, battery and (I assume) ignition (since it will start)   There is a third wire, but it is not connected to anything at the moment.  I have not yet begun to explore the intricacies of the electrical system on this project, so I'll leave that for now.

So my question relates to the non-battery wires.

My new alternator is internally regulated and  has connections for "field" and "stator"  (along with the main battery connection).  Which one would the instruments hook into? 

Since there does not seem to be electrical connectivity, when at rest, between the battery terminal and either the stator or field connection, how does the ignition switch get power? Do I hook the switch wire directly to the battery connection? 

 

 

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I would @$$ume that the wire going to the cluster is for the charge indication idiot light, and you won't need it unless you have that type of cluster.  With a keyed (ignition) wire and a battery connection that should be all it needs to charge.

 

That said, not all alternators are the same.

 

Is this a unit that is listed as being a direct replacement, or are you trying to retrofit something else?

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12 minutes ago, ruralandalone said:

It is a Powermaster SI type, high amperage, single wire replacement.

 

Hi rural,

 

I am confused. a "single wire replacement"  actually is a "self exciting regulator" setup and only requires 1 wire total.

 

Do you mean 1 wire total, or 1 output wire and 1 regulator wire? Perhaps a link to the alternator would help.

 

From Powermasters website

 

How do I hook up a one wire alternator?

 
 
 

Simply run a charge wire from the battery terminal on the alternator to the positive terminal on the battery. The onw-wire regulator is a self-exciting regulator, meaning that it has sensing ciruitry for alternator rotation. As the alternator starts to spin, this circuitry connects the internal voltage regulator to the battery and turns the alternator on. When the alternator comes to a complete stop, this same circuitry turns the alternator off.

 
 
 

 When to use a one wire alternator?

 
 
 

Powermaster early style Delco alternators will work either way - as a one wire or OEM style. The main difference between a one wire and an OEM is the method used to energize or turn on the alternator. An alternator using the OEM style is turned on with the ignition switch. The one wire design is energized with a special sensing cicuit built into the internal voltage regulator. This circuit senses the rotation of the alternators rotor. The rotor must turn at sufficient speed to trip the circuit, starting the charging process. This turn-on speed is affected by several things and is typically higher with certain high amperage alternators. Once this circuit is tripped, the alternator will charge at all speeds, even very low ones, until the alternators rotor comes to a complete stop. At that point, the circuit will shut off and wait for the process to be repeated. What this means for the consumer is that in some applications the engine must be revved to 1200 or 1400 RPMs to turn the one wire alternator on. If the wiring harness is available and this characteristic is annoying, then Powermaster alternators can be plugged in like the stock unit and operated with the ignition switch.

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Hi rural,

This information is based on a 1988 wiring diagram. I imagine yours is the same, but don't know this with certainty.

 

The original equipment alternator had three wires going to it. One, a larger 8 gauge red, goes to the battery terminal. This is hot all the time. 

The connector at the regulator has two wires coming to it. One is a 16 gauge yellow, the other is a 16 gauge tan with white tracer.

The yellow should be hot whenever the ignition switch is on.

The tan with white comes from the instrument panel gauge, or idiot light if there is no gauge. This will be hot when ignition is on, but it does not receive full voltage, it receives the voltage that passes through the gauge, or idiot light.

 

I'm not quite sure of the electronics, but for the stock alternator to work, the yellow wire has to get full voltage, and the tan with white wire has to have a 10 ohm load between full system voltage and the terminal on the regulator. This 10 ohm load is either the voltmeter, or the idiot light.

Neither of these supply electricity into the ignition switch. Both supply electricity to the voltage regulator, which powers the alternator field, which allows the alternator to produce electricity.

 

To answer your question specifically, view the alternator from the back, so the pulley is facing away from you, and the regulator is facing up.. The left terminal, #1,  should have the tan with white wire, and the right terminal, #2,  should have the yellow wire.

 

Hope this is helpful.

Gene

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Gene has it exactly right. I believe the 87-90 Renix jeeps used the same alternators as 84-86 XJ/MJ.

Besides the 86 2.5 is the first year of the Renix.

 

The 12si is just a standard GM alternator.

On my 85 XJ with 2.8 GM v6 (1986 engine harness) that powermaster alternator would plug right in.

Your 1986 2.5 uses the same alternator as the 2.8 V6, as long as your alternator plugs exist now you should just plug it in. If those are damaged you can find a plug with pigtail to repair the two prong plug.

 

 

 

Sent from my iPhone using Tapatalk Pro

 

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First of all, I have to apologize, because I am full of crap and most of what I said previously is in error.

So lets start again.

My current wiring is as follows: Medium heavy red wire to the back of the current alternator.  Medium heavy red wire to the side of the alternator.  Brown wire with stripe to side of alternator.

Heavy red wire going from battery to the wiring harness (heavier than those on the alternator.  I don't yet know where this goes, and I will have to open the harness to find out.

Assuming that I replace the wire on the back of the alternator with something heavier and run it directly to the battery, do I NEED to hook up the other wires, or should I simply plug them into the new one and assume the wiring is the same?

 

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Hi rural,

 

Sounds like this is getting complicated. I found this thread

 

 

 

Of yours, so it sounds like there has been quite a bit of rewiring going on.

 

Perhaps you can look at it this way. The alternator output, from the larger stud on the alternator, is 12 V hot all the time. Essentially it is the same as the positive terminal on the battery. If you're running extra wires to a winch or other accessories, there may be several wires, but basically the alternator output goes to the battery.

 

I'm not sure what the additional red wire on the side of the alternator you're speaking of is, a picture would help. Is it possible that is actually a ground wire, if it's connected to the frame?

 

The regulator plug has two wires. Normally both of these have to be connected for the alternator to work. If your alternator would function as a "one wire" alternator, then this hookup would be optional. If you don't hook them up, then the voltmeter in the  dash  will not work.

 

Again, pictures might help.

Gene

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The winch and electric pump are not in the equation - yet. 

As far as I can tell, since this is a "1-wire" replacement alternator, I don't HAVE to hook anything up but the direct link to the battery.  This wire has to be added because the original does not appear to go directly to the battery and the gauge is too small.  When it gets a bit warmer I'll deconstruct the harness and find out where the two red wires actually go.  My thought at the moment is that I will connect the 2 side wires as well - although perhaps not at first.

I'm not sure how much wiring has been replaced, but I don;t think too much has changed from OEM.  The problem is my lack of understanding.  This is much more complicated than my 50's and 60's vehicles and I am, at best, feeling my way.  So I very much appreciate everyone's comments!

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The idiot light doesn't do squat. Mine does not come on when my truck is running but does when the key is on and not running. Sounds like it's working as it should, right? But if I pull one of the cables off the battery it dies - which means the alternator is NOT working yet the light is not coming on. 

 

Anyway, good luck with it. 

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I’m not sure what the difference between one wire set up and two, I would think the voltage regulator would need at least one line in the plug to work.
the 94 amp alternator I put in my XJ says the same thing about one wire or two and I just hooked it up normally.
Bottom line it’s a 12si alternator replacing a 12si, just the new one happens to be more powerful.


There is another upgrade got 12si alternators where a newer GM alternator is used, that more complex, they sell kits to adapt it. But this is the same alternator going back.



Sent from my iPhone using Tapatalk Pro

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I used a 4 gauge charging wire. On the 88 the wire goes to the starter relay. I used a MEGA Fuse, 175amp (IIRC) between the charging wire and the starter relay. If you need a pic of that I will get one tomorrow.

 

You will have a post for the charging wire and a plug for the two wires.............that's it. The only thing you need to consider is the size of your charging wire, other than that, it's a simple replacement. 

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Just a brief follow-up.  I had a quick look at the wiring (it's still cold out there!) and it appears that the red wire on thh side of the alternator (rotor) and the red wire on the back join together close to the alternator, and then run back to a fusable link and then to the battery.  So when I replace the alternator and charging wire I won;t bother with the side red wire.  I'll just hook up the voltmeter.

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