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Thread: Prestolite ICM - Not Required for this setup?? 75í CJ5 304 V8 Reply to Thread
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  Topic Review (Newest First)
07-11-2018 12:25 PM
PottsyCJ5 Thanks for the powermaster recommendation. Iím pretty clueless about alternators and I value your opinion.

I think I definitely want to go with an internally regulated alternator just because it seems simpler. Reading up on some of JeepHammers old threads for how I would need to re-wire in order to do so. The PO has the Motorola external regulator still installed and wired up, but itís possible it is not really in use based on what I found with the ICM.
07-11-2018 07:34 AM
Matt1981CJ7 Assuming yours is still the factory external regulated alternator, I'd upgrade to a internally regulated unit rated for 100 amps. I like my new Powermaster unit a lot.

Good luck,

Matt
07-11-2018 06:23 AM
PottsyCJ5 Thanks, Matt. I appreciate your help as always. I owe you a considerable amount of beers ; )

Alternator looks original so itís understandable. Is there an alternator for the 304 folks recommend? I am considering a dual battery setup but not quite ready for all that just yet. Any alternators out there that would work for one or two batteries so Iím future proofed if I expand the system?


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07-10-2018 07:04 PM
Matt1981CJ7 Nice work, brother.

All symptoms point to a failing alternator.

Matt
07-10-2018 06:43 PM
PottsyCJ5 Thanks Matt. So here is what I am seeing. FWIW the battery had been on a trickle charger prior to starting these tests all light and indicates battery was fully charged.

1) Neg Terminal disconnected and test light between neg terminal and neg cable does not light up
2) with engine off voltage at battery b/w terminals = 13.18V
3) with engine off voltage b/w red alternator cable and neg battery terminal = 13.18V
4) with engine running voltage b/w battery terminals = 12.98V
5) After 10 mile drive voltage b/w battery terminals = 13.08V

Also, i disconnected the ICM and reran the test b/w the alternator and neg battery terminal and it read the same 12.98V with the engine running, so I think that rules that out.

Not sure what this indicates. Weak alternator? Belt seems tight enough but I donít have a belt tension gauge. While driving around volt meter hovered around 13V the whole drive.


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07-10-2018 11:21 AM
PottsyCJ5 Thanks Matt. Iíll perform both those tests tonight.

If I see I am getting 14 volts at the battery with engine running as I should, Iíll also try disconnecting the ICM again just to prove itís not related.


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07-10-2018 09:52 AM
Matt1981CJ7
Quote:
Originally Posted by PottsyCJ5 View Post
Matt - I do have a test light and a multimeter. I will try that test as soon as I get home. So I connect the test light to the negative battery cable and directly to the negative battery post?
Connect the test light to the disconnected negative battery cable, then touch the test light probe to the negative battery post. If the light goes on, you have a parasitic drain.

To test the alternator voltage output, use your multimeter at the battery first with the engine idling. You should have around 14.4 volts. Then test the large red wire at the alternator. It should have the same voltage, or very close.

Matt
07-10-2018 09:41 AM
PottsyCJ5
Prestolite ICM - Not Required for this setup?? 75í CJ5 304 V8

Matt - I do have a test light and a multimeter. I will try that test as soon as I get home. So I connect the test light to the negative battery cable and directly to the negative battery post?

John - yep, I only disconnected the box on the left. In that photo you can see the 4-wire plug is already disconnected and then I also disconnected the smaller black wire you can see in that photo that connects to the solenoid middle left post (I forget if that post is the ďIĒ or the ďSĒ post).

What is the best way to test if the battery is being charged with or without the ICM plugged in? I want to test the output at the alternator but not sure which terminals to test with the multimeter. And how can I test that the current is actually making it back to the battery when engine is running and the battery should be charging?

Temporarily I have plugged the ICM back in until I can find out whatís going on. This definitely started right after disconnecting the ICM, but I understand it ďshouldnítĒ be related.


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07-10-2018 08:08 AM
John Strenk Well looking at the schematic, it shouldn't matter.

Did you just unplug the one on the left?


The one on the right controls the charging.

Here is a schematic of your 1975 charging circuit for a V8.
It looks as if there is a sense wire that is attached to the power input to the ICM.
But disconnecting it should not effect the charging.

Unless he ran new wires to power the coil and cut out a lot of that circuit.
But then it would of not worked at all.

Is it charging with the ICM hooked up? Verified with a volt meter?
07-10-2018 07:31 AM
Matt1981CJ7 The old ICM should have nothing to do with the charging system. I think you have other issues going on.

FYI, the 4 wires from the old ICM should be as follows: Green and red w/tr wires went to the old coil, yellow and blue wires to the old distributor. As I stated earlier, the old ICM and all if those wires can be removed without causing any problems.

Do you have a test light? If so, disconnect the negative battery cable. Attach the test light clamp to the cable and touch the probe to the neg battery post. If the light goes on, you have a parasitic drain that you need to hunt down.

Matt
07-10-2018 06:51 AM
PottsyCJ5 Update on this...it seems removing the ICM has caused my battery to start draining. Jeep left me stranded twice.

The Jeep was starting and running fine for two weeks with very minimal driving (probably only a couple trips) after taking out the ICM. The ICM only has two plugs - one single wire plugs that connects directly to the starter solenoid, and another with 4 wires that connect with a plug into a harness and I canít tell for sure where it goes from there.

I suspect what is happening is that when the PO switched back to a points dizzy, the wiring was not changed and the ICM wiring is somehow in the circuit the alternator useds to charge the battery. Since taking the ICM out and not changing any other wiring the battery was not charging while driving. Battery is only a couple months old so I think it took a bit to drain completely making this not immediately apparent.

Does that make sense or do you think I have something else going on? Jeep had never left me stranded or had any starting issues prior to this and starts on the first go when the battery is fully charged. A jump from my truck got me back on the road both times and I have been leaving the battery on a trickle charger, and it will hold 12 volts after being charged. The battery issues definitely seem directly related to removing the ICM.

For now I just put the ICM back in as well, though this time I put a piece of cardboard under it to act as a heat sink to hopefully stop the oozing.

Side note - Would fully draining the battery reduce its life? It was a new Napa battery and I hope I didnít cook it.


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07-06-2018 10:54 PM
CSP
Quote:
Originally Posted by John Strenk View Post
Would that give him one for an AMC distributor or should he choose a different application because he has a GM distributor in there?
Jeep used an AMC variant of the GM distributor in the early 70s, prior to Prestolite. This is what his engine has in it currently.

It's the same concept as '78 and up CJs having the AMC version of Ford's Duraspark dizzy.
07-05-2018 02:00 PM
John Strenk
Quote:
Originally Posted by PottsyCJ5 View Post
Going broke indeed John and my wife is starting to reach her limits for how much Iíve been in the garage. Gotta start spacing out my Projects better and alternate home projects in between ; )


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Your jeep is running, Redo her Kitchen. Then get back to the jeep later....
07-05-2018 06:56 AM
PottsyCJ5 Going broke indeed John and my wife is starting to reach her limits for how much Iíve been in the garage. Gotta start spacing out my Projects better and alternate home projects in between ; )


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07-04-2018 08:42 PM
John Strenk
Quote:
Originally Posted by CSP View Post
Your application would be any '72-73 CJ with the AMC 304 engine.
Would that give him one for an AMC distributor or should he choose a different application because he has a GM distributor in there?
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