90 SHO Alternator Overcharging

[sperold]

With a battery charger, I charged up the battery on my 90 Winter Car, to make sure it did not have to work too hard to recharge the battery.
Started the car, and my battery light is on.
Much to my surprise, when I put a gauge on it, the alternator was at 15 Volts at the idle speed.
I swapped out the battery and the reading was the same.

What goes on inside the alternator to begin the over-charging situation.
I do not relish the removal of the alternator and going to a repair shop, so I am asking if there are any things I can do to get it to charge properly.

Any ideas or advice is welcomed.

 

[rubydist]

The regulator is bad. idk if the Gen1 cars are this way for sure, but all the Gen2 and later Ford vehicles have the regulator built into the alternator, so I suspect you 90 is the same way. The repair shop can re-build it with a new regulator.

 

[sperold]

Yes, the little 90 amp alternator has an internal regulator.

I hooked the charger up to the battery in the car, so I think I may have contributed to the failure, which makes me remember that no good deed goes unpunished.

Thanks for the diagnosis, any chance it just died of old age?

 

[SHOVNST]

90 and newer have the internal regulator. 89 and older is external.

.

 

[rubydist]

I do not think you charging the battery had anything to do with it. Unfortunately, the regulators were not very durable.

 

[sperold]

Big surprise.
Took the alternator off the car and went to the rebuild shop. They did their run-test and found that it is 15 v at an idle and 15V at any rpm. He said the amps came down as it ran, and there was nothing to be alarmed about and that he would have no problem running it in his car. Especially in the winter.

When I told him the battery light was on, he insisted that was not the case.

I remember reading on this forum that overcharging turns on the light, just the same as under-charging.

Anyone have a recollection of how the charging above 14.5 V turns on the light?

 

[sperold]

With some luck, i found an explanation of why the battery light is on when overcharging. The post is from ShelbyDoug in 2005 and is titled "Charge Indicator Light help" and the explanation is from
Hawkeye 18, post #5.

I went back to the shop and told them if they can still buy a regulator, to put a new one in my alternator.
The new regulator has to be soldered into place, and it seems that is not a fun job.

Bad news is everyone will be hunting next week and they won't have a part by then, but that is life.

https://shoforum.com/index.php?threads/charge-indicator-light-help.110030/

 

[sperold]

The shop could not buy a regulator for the alternator, so they put it back together and tested it again. It is still doing the 15V output at all rpm.

While apart, they showed me green dots all over the windings, and explained that they were breaks in the coating on the wires and the green was corrosion; and it is on borrowed time.

I put it back on the car and drove it around for half an hour, then felt the battery; and it was stone cold.

I found another alternator, and plan to have it tested when deer season is over.

A side note, the shop told me to run a heavy gauge wire directly from the alternator output terminal to the positive terminal of the battery, if I wanted the battery light to go out. But I did not do that, as my bravery only goes so far.

I will be able to buy a new alternator or a rebuild from RockAuto, but with the border to Canada being closed, it is subject to a lot of extra charges and taxes.

 

[sperold]

Story gets stranger.

My 15 V alternator eventually failed, and I got another used alternator. Strange thing is: it does the same thing, puts out 15V at all rpm.

I broke down and bought a new (or rather rebuilt) alternator from RockAuto, spent a cold afternoon installing it, and guess what: it puts out 15V all the time.

All of these alternators cannot have the same fault and failure method, so I am looking for some more help. Anyone have a theory on what could be the issue. I am going to go through the wiring coming off the positive terminal, I see an inline housing that looks like a fuse holder, but other than that, it is just wiring and nothing seems out of place. Could a ground be responsible?
I have the "Vacuum and Electrical Troubleshooting Manual" and so far it has not helped.

 

[rubydist]

15V is at the high end of the range for what the alternators should be putting out, so the guy at the shop is not wrong in saying it should work fine. However, the light system in the SHO is not happy with that. It may be that it would not be happy with any voltage output.
The system, iirc, measures a voltage differential and if that is too great the light will come on. This suggests that one of the components of that measuring system is bad - maybe a cap or resistor that has opened or shorted. That would be the next thing to look for. Do you have the wiring diagrams?

 

[sperold]

I have the Electrical and Vacuum Troubleshooting Manual.

By running the accessories, which is very desirable in the winter (heater, rear defogger, lights, and fog lights), the voltage is 14.7 at all highway speeds.

I took the cartridge thing apart near the positive post of the battery, but I did not know what I was looking at, and it seemed like an elaborate connector.

So not a lot of progress so far, but at least it is workable.

Thanks for the comments.

 

[rubydist]

Is the battery light still on at 14.7V? Or does it go off at some point along the way?

 

[sperold]

At an idle, with the accessories on, the voltage goes down to 12.5V to 13V, but the battery light never goes out.

I tried the wire directly from the alternator terminal to the positive battery post (which was supposed to cancel the battery light), but the light stayed on and all the readings remained the same.

I don't know if my strategy of running the accessories is a good thing, but that is my method until I hear differently.
I feel a lot better when my volts are down from the maximum.

My underlying problem is that I do not have enough basic understanding of electricity / electronics for the EVTM book to help me. For example, I don't know where the capacitors or resisters would be, and once the outputs of the alternator enter the inputs of the ECM, BCM or CCRM, my eyes glaze over trying to understand what they are doing.

 

[rubydist]

I only have the 92 and 94 wiring diagrams, and iirc the 90 is enough different from the 92 that what I have won't be right for me to help you know where to look, sorry.

 

[sperold]

Thanks for looking,
The 92 still has the little 90A alternator, so the charging system will be similar. It will have different wire numbers and colours, for sure, but the architecture will be close enough.
I too have a 92 EVTM, if you show me the circuits that can affect the alternator output, I will look them up and cross reference to my 90.

This is not the start of a long term commitment to diagnosing my issue from you. If I get a shove in the right direction, I can take it from there.

Thanks again for looking and responding.

 

[rubydist]

ok on the 92 wiring diagram, the SHO alternator is in zone 22A. The alternator output is circuit 38 which goes through the fuseable link to circuit 290 to the power distribution box. The power distribution box feeds power to the vehicle, including the instrument cluster.

The other side of the sensing system is circuit 904 which goes to the instrument cluster 18 pin connector as pin 14. zone 104D

Unfortunately for us, they don't show us what that circuit looks like inside the instrument cluster. So, the next step I would take would be to swap in a different instrument cluster and see if that solves the problem. Or alternatively, you might confirm there are no opens or shorts on circuit 904. Either way, I think you are going to have to pull the cluster.

 

[luigisho]

How's that for detail. Nice.

 

[sperold]

That is a good plan, and I do have another panel somewhere. I will concentrate on the power distribution system first and see where that takes me.

I just finished a 2 hour highway drive to my city property and I kept the voltage output under 15V by running various accessories, and it did work out OK. It is such a change for me as I always minimize accessory use, and never drive with all the lights on in the daylight.

Thanks for the advice.

 

[sperold]

I have an observation, and I am reporting it without any effort to explain the situation.

I put a voltmeter in the car, sitting in the ashtray and 2 wires run directly to the battery, so it is a battery monitor, so to speak.
During the winter, I have not driven the car much, so there are not a lot of hours on the car since I noticed this charging issue.

The latest observation: when I start the car, the voltmeter reads in the 15 V range and the battery light is on. I turn on lights and accessories and the voltage drops into the 14 and below volts. After about 3 minutes of operation, the red battery light goes out. I can shut off all the accessories and the battery light stays out. I can raise the RPM and the battery light still stays out. And it was a fully bright light, not the dim one that you have to be in the dark to make sure it is really on.

This change has occurred without me altering anything on the car. So I am happy, but stumped.