Alternator Overcharging

[xatu40]

Have an unusual situation that I hope maybe some one else has already been through. Will try to keep is short and simple. 83 with 4.2 and manual tranny. Was trying to diagnose an ignition problem (no spark at coil, except when getting on the key or getting off of it) for a while, then once I got into is, figured I'd replace most of the components due to age. Still no luck, so had it towed to my local shop. Mechanic called on Friday and determined the ignition control module was defective (I had come to a similar conclusion following the service manual checks and had just replaced it.) He had an aftermarket ignition module sitting on the shelf and wired it in and it started right up. Though he said he was getting 16+ volts at multiple locations. Vehicle would not shut off with key, until he disconnected wire at alternator. Put another alternator on it today, and same problem. Unless it happens to be two alternators with bad regulators, any other suggestions for what it could be? I'm going by shop tomorrow afternoon, so hopefully be able to get more details then.

Appreciate any suggestions. Thanks.

 

[cbford]

If everything is stock, you have a delco SI alternator with a 2 wire clip or plug and a batt terminal (regulator is internal). Sounds like you may have a problem with the S (sense) wire. The two terminals are labeled 1 and 2, 1 is the field or excite wire, it should be a resistor wire if your jeep is stock and needs to have 12v when the ignition is in run position. The 2 wire or "sense" wire needs to attach to any 12v hot supply when key is in in run. This reference tells the alternator how much amperage to output to maintain system voltage. I would also suggest you add a ground from the case if the alternator (usually a little tab with bolt hole for this) to the negative post of your battery. If all is well your voltage should be between 13 - 14.2 ish volts on your voltmeter or at the pos. terminal of your battery. Do you have a 12v tester or multimeter?

Something else to check is the resistor wire connected to position 1. This "fusible Link' is an Alloy wire designed to burn out at a specific amperage load, with special insulation designed to keep the wire from totally melting and burning through harness.

They work like a fuse, but are more tolerant to minor or brief overloads so they are more robust in a use such as feedback circuit with varying voltage/amp draws. Occasionally, 'Fusible Links' will pop or corrode through without warning... If yours is original it's probably past it's prime.
To identify a fusible link, unwrap the harness just below the starter relay...
The fusible link will be the medium size 'Pink' wire, it will be attached to the 'Battery Cable' side of the starter solenoid, so BE CAREFUL or unhook the battery before you mess with it. The fusible link will be about 5" long, (this matters too, length = resistance in this wire) and it will terminate in a plastic collar where it connects to the regular wire initiating the charge field in the alternator. You can get a new one at auto parts store if you think yours is bad.

 

[xatu40]

Thank you very much. That was a lot easier to understand than the text in my service manual. I am on the road this week for work, but will use my multimeter and follow the steps referenced above. Battery always gets disconnected before I started messing with connections. Thanks again.