we have a 1989 ford bronco and last week our battery light was comming on so we got the alternator checked?

I would start by checking the battery cables. The guage flickering tells me you have a loose connection. This could also cause the warning light too come on. If all of that is good and you still have problems double check too see if your new alt. has the proper amperage for your vehicle.

It sounds to me like the voltage regulator. I had an old Dodge Diplomat that when i drove it at night, all the lights would be very dim for a while, then very bright for a while, etc. Also, i would get a strong sulfur smell, like the battery was overheating. I took it to a parts store, and had the system tested, and it was the voltage regulator causing the problem.

It sounds like the voltage regulator isn't working right. It is internal in the alternator. Chances are the 'new' alternator is bad. I don't think that is why your check engine light is on unless it is way over charging. I'd have it checked by a tech.

alternators have internal voltage regulators, since you have a new alternator you also have a new voltage regulator.

check the belt for tightness and or slippage.

check all the wire connections from the battery to the alternator , make sure they are clean and tight.

the fact that the check engine light comes on makes me believe that it`s the belt.It may have oil or grease on it and is slipping.

Check or replace the voltage regulator. Same thing happened to me on a dodge truck.

voltage regulator is good answer...but I think its inside alternator for many years now.ford bronco or bronco II?

Check cables and battery and clean all connections

check your connections at alt. and at battery must be clean and tight if not it can cause alt to fail again.

have youe alternator retested if it is a lifetine warranty it may mean you grt to spend your lifetime replceing it