Do they dim down at low RPM then brighten when you accelerate?
Are they switching between High and low Beam on their own?
First thing to do is clean, and tighten all your battery cables. (AT BOTH ENDS!)
Next inspect your grounds, especially at all the lighting buckets. Burnish off all paint grease and dirt from the surrounding area, add a star washer and a lock washer, and tighten back up.
BE sure you have a central Ground point for your cables at or near the starter on the engine block. Battery cable, one to the frame, and one 10 gauge wire to the firewall, and another to the alternator ground lug, or mount bolt.
Answer the above questions, maybe we can offer more help.
well..the lights get bright...then go straight to really dim and back and forth. it doesnt matter what rpm is getting put out. they dim and brighten either way. it has never done it before the new alternator....but when i did put the new alternator on the lights had gotten the brightest ive ever seen them.
I've seen that happen quite often on aftermarket rebuilt units. Factory rebuilts rarely do that, but the ones from the discount parts houses can be bad. You may have to try several alternators to get a good one.
If you are SURE the Grounds are all Good, The BELT is tight, and The Battery is in Good Condition..
I'd FIRST take the alternator BACK where I got it and have it tested..Sounds like a failing regulator.
Check to be sure the Alternator is wired correctly (if you had to modify anything, or not maybe the last guy did..)
TERMINAL 1 = Alternator output wire, 10 gauge, goes to Fuse link (if none, a good idea to install a proper one, pre 70's did not have them factory installed) and The big bolt on the starter solenoid Or Horn relay power terminal.
TERMINAL 2 = Red wire, 18 gauge, Regulator sensing, goes to terminal 1 OR to the horn relay power terminal or any 12 volt source.
TERMINAL 3 = Brown Wire, 18 Gauge, Goes to the Charge lamp circuit.
TERMINAL 4 = Black 10 gauge wire, Ground lug, goes to your central grounding point at or near the starter on the block.
You'll want to verify these are correct and connected to the proper circuits.
If all checks good, and the Red Regulator wire is connected to the output wire Terminal 1, (or the same connection at or near the battery) move that wire to the Horn relay power wire or any 12 volt source not directly at the battery, this will give you better remote sensing..(regulator on earlier , and longer ) Then it would at a direct battery connection.