Wrangler sputters when headlights are on

Hello- hoping you folks can point me in the right direction?

My brother in law has a '90 Wrangler. We were driving to the store today, and when he turned the lights on, the vehicle started sputtering and stuttering. I looked at the ammeter, and it was going nuts. As soon as we turned the lights off, no problems.

Going to check everything with a voltmeter later today when I get off work, but in the meantime- any known issues of this nature been mentioned or experienced by anyone previously?

Thanks in advance,
Steve
 

I'd start with all the connections and grounds. Check the battery >12V and alt output volatge >14V. I had an issue like this in my old 95 F150 with the ammeter jumping. It was th brushes shorting out in the alt. new brushes and about 1/2 hr back in business.

Any other electrical component do this like blinkers, radio or heater/air fan?
 

sounds like voltage regulator to me,some voltage regulators are built into the alternator,which means that indeed you need to replace alternator.If it is not built into the alternator,I believe it'll be located on the firewall.
Befor buying anything,find out for sure where your voltage regulator is located.
 
Sounds like the ground wire to the body is loose or missing. That would require the ground for the ignition system and headlights to travel through the engine, trans, driveshaft and Ujoints to the axle and springs, then back to the coil, lights, etc.
 

WOW 4 sounds likes in a row :):D That's gotta be a new record
 
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