twitchy alt gauge

[Whateverman]

I can't remember if my ride's cab donor had this issue or not and the alternator (& brackets etc.) donor Lincoln towncar had idiot lights instead of gauges...and my patience as far as electrical gremlins go this week are at a low point so I thought a little input from others would be a great idea : the battery's holding a charge and seems to charging fine (I haven't broke out the test equipment yet), The voltage reg is a factory unit circa 1970 ( i'm kinda thinkin its the culprit but i've been too busy fixin other junk to replace it yet).. the alt gauge twitches around like its having a seizure and if the engines running with the door open the interior light flickers enough to cause a seizure....
any suggestions?

[Mancar1]

I would have my alternator checked. Sounds like it may be the problem. When you test the alt output at a fast idle, your test meter should read around 14 volts. If it reads less than 12 you may have a bad alt. Hope this helps.

[fordman]

what is the alternator off of? the lincoln or the truck. what year is the lincoln alternator if you are using it?

[Whateverman]

i'm hoping its the reg too,i have a few kickin around in the garage somewhere.
the alt's off my ol' pimpbarge from hell '88 lincoln towncar ( i miss that tugboat)....i saved some parts off her when i kicked 'er off to her next life as rebar in a chinese hotel,i'm running the alt & ps pump (crank/waterpump pulleys and related brackets) off it in my rig (i had to relocate the alt to the drivers side of the engine)
..i think i have an extra alt too ,maybe hopefully...the parts places in this area are painful to deal with ....
yeah,so i wouldn't doubt it is both the alt & reg,guess i'll check it out with the test meter tommorrow
thanx guys

[fordman]

i would say the 88 alternator has its own internal regulator. so it is running two of them and that may be whats causing the twitchy gauge.

[Whateverman]

no,the 88 lincoln alternator is externally regulated ( and uses a ribbed belt) - I made sure of that before I installed it -unlike the 90 mustang one i was gonna run (with the mustang's serpentine belt setup which woulda been pretty nifty i think)
I'm pretty sure this alternator has some issues and i wasn't gonna use it,so i won't be shocked to find its buggered when the clouds lift and it stops pouring around here so i can go check on it

[Alfred Lord Tenniscourt]

I agree with everyone that the voltage regulator is the first place to look, and that the alternator is the second, but I would look at the grounds third. I had a bunch of weird, intermittent problems in my truck for a little while (bright lights would flash when the blinker came on, luminosity of cab lights was all over the place, etc, etc) and though I wouldn't have thought it possible because of all the metal bolts holding everything together, it was because the chassis grounds were not solid.
The ammeter never uses a chassis ground, so it wouldn't seem like that could be the problem, but if the alternator doesn't have a solid ground to the chassis and body, it might be possible that the bad ground is causing the voltage regulator to spazz out by constantly varying the voltage it sees between battery and ground.
A loose connection at the starter relay could do it too...
Good luck!

[Whateverman]

thanx, we've had torrential monsoons for the last 3 days and today the temp plummeted and there's 2 inches of sloppy pacific coastal packing snow all over everything - and being that the ol' lady doesn't allow my ol' truck anywhere's near the garage anymore...well,lets just say I'm being forced to hold off on checking this problem out for now

[Whateverman]

well- here we are 4 months later and finally the clouds parted long enough to check things out - the voltage reg i was running was a 40amp'er out of a 67 ford school bus ( I used it in my rad support donor and never bothered removing it when i swapped the support) ...totally old school unit with adjustable points in it .it was pretty crusty but it checked out good, i replaced it with a new one anyways.
while i was removing it the culprit in this twitchy tale was uncovered- seems the ground wire running from the alt to the reg had broken free from the ring connector that attached it to the reg... so there we go,case closed thanx to everybody for their help
Sir Tenniscourt gets the cigar