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Alternator quit charging right after cluster swap - Ideas?


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Good afternoon All,

Ok, so I just swapped my cluster to get rid of the dummy lights last week and I realized today that my battery is not charging anymore. I have 12v (ign on) at the sense (yellow wire) and good continuity from the output wire to the battery. My question is on the small brown wire on the alternator that used to go to the light. Is this wire an exciter wire like the old gm ones or only for the light? I have no voltage reading on that wire now after the swap (key on or off). I know it went to the negative side of the charge light before, but the schematics for the gauge cluster doesn’t show anything for that wire now. Thoughts? Should a setup an exciter wire with diode for it? Maybe alternator just quit, but it seems weird to have occurred right after swap.

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Year and engine would be helpful for correct diagnosis

You can add the info in your signature so that you don't have to put it each time. Link in my signature on how to do it

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Year and engine would be helpful for correct diagnosis
You can add the info in your signature so that you don't have to put it each time. Link in my signature on how to do it

Jdog,
Great idea, the truck is an 88 with a 2.5.


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Some additional information if it helps.  The alternator worked fine before the cluster swap.  The alternator shows good when tested on the bench at O'Reilly's. I put a diode  in between a switched 12v on the tan wire as some have suggested in other forums and still no charging.  Yellow wire does have 12v ignition power.  I do understand from the 88 electrical manual that the tan wire should not be needed with the gauge pack, but it seems weird that mine just quit after the swap. I ordered a new alternator just in case and it will be in tomorrow. Maybe the good test at O'Reilly's was false?

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It is recommended to download the electrical manual to help with this. It includes some diag and troubleshooting to help figure this out. You could always do it the old fashioned way and start the truck and disconnect the power cable at the battery post to see if the alt is producing power like it should. 

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I apologize for my stupid questions in advance.  I am new to Renix jeeps.  Most Gm CS130 alternators use the PLFS connector where only the S (sense) wire and the L (lamp) wire are used but it seems the Renix system uses only the L (lamp) connection (tan wire) and the F (field) connection (Yellow wire on mine.

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4 minutes ago, Ωhm said:

Cluster swap should have no effect on charging voltage. Check the condition of Fuse Link A (BLUE) at the starter relay stud.

That's what I figured. Continuity is good at the fusible link A. I checked that before my original post and again this morning.

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5 minutes ago, eaglescout526 said:

It is recommended to download the electrical manual to help with this. It includes some diag and troubleshooting to help figure this out. You could always do it the old fashioned way and start the truck and disconnect the power cable at the battery post to see if the alt is producing power like it should. 

I have the electrical manual.  Alternator is definitely not producing while on the truck. 

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2 minutes ago, eaglescout526 said:

What is nice about the Renix set up is you can swap from lamp to gauge without having to change a thing. That being said, it is also a GM charging system if that helps. 

Yes, that's what's weird since most GM systems require an exciter signal from the Lamp wire, but the diagram shows a  dead end on the tan wire on the gauge cluster setup while utilizing the traditional exciter setup on the idiot light cluster.

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I think the early XJ's and MJ's may have used that platform when they had the 2.8L but, AMC probably ditched that for GM alt and adopted something Renault probably came up with when they partnered with Bendix

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2 minutes ago, eaglescout526 said:

Then the alt couldve simply given up the ghost. Do you know anything about it? Stock or aftermarket reman unit?

Alt tests good on bench (O'Reilly's) but not on truck.  I was trying to figure out what terminals they use for testing, but no one seems to know. I do have another alt on the way just in case.

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Ok, so today I got the new alternator installed and still no charging :furious3: I wanted to explain what I figured out to possibly save someone else the trouble in the future.  I figured that I needed to go back to the cluster swap again because that's when it started acting up.  Everything I read online as well (as everything I've been told on the forums) is that the Tan wire dead ends at the cluster with gauges and is only used on the cluster with dummy light. The yellow wire did not change and tested good at alternator pigtail.  I pulled the cluster again and inspected it more closely where the tan wire goes in at the back.  Turns out that the tan wire goes into a diode built in to the cluster assembly that has an ignition power on the other side.  This diode takes the place of the dummy light circuit and acts as an exciter to the charging circuit in the alternator.  It is required for the alternator to charge.  The tan wire does NOT dead end at the cluster as the diagrams show.  Rather than disassembling the cluster which can be done without that much trouble, I opted to install a new diode inline between the tan wire in the harness and the ignition feed that runs in to the diagnostic connector under the hood since they are right next to each other.  I ran down to the parts store and picked up a Standard connector adapter(part #S792) to use the diode from it (old chevy style).  Crimped and shrink wrapped all connections, and now the alternator charges fine. I think I'll just keep the new alternator installed and keep my old one as a backup.  Now that we are charging again, I can resume my cruise install and move on to the A/C system before spring.  :banana:

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4 minutes ago, Greentoy said:

I pulled the cluster again and inspected it more closely where the tan wire goes in at the back.  Turns out that the tan wire goes into a diode built in to the cluster assembly that has an ignition power on the other side.

 

Probably too late for a photo. But for myself, lesson learned here.

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This is the part you need on the yellow wire.  You will need to cut out the yellow wire, crimp the side that has the black connector to the tan wire and the other side to an ignition 12v circuit ( I used the diagnostic link input wire) 

s792.jpg

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