Alternator check? Need help tonight!

artart · #1 (**permalink**) 07-02-2003, 08:12 PM

Just fired my Spider back up after adding a CD Changer and amp, new battery and new top! While I was wiring up the sound stuff and in the process of disconnecting the old battery I accidently caught the positive side into the trunk , slight spark no biggie (I thought)
During my checkout of the sound sytem completion noticed that the battery would not take a charge so I swapped it out,cleaned the ground while I was swapping to the new battery. Everthing starts and runs well getting ready to take it to the convention tommorrow and ran a shakedown run tonight. Immediately noticed a low glow on the charging idiot light, then checked to see the voltage meter reading below 12! Previously read just above 12. Ran around for 15 minutes and noticed that at idle meter reads right at 12, on takeoff the light glows brighter and the oil and brake lights are coming on as well, get to crusing speed they go off, still a slight glow on the charging light.
As an American shade tree mechanic we always tested alternator for output by pulling the positive cable off the battery while the engine is running, if the motor stalls you know their is no charging going on. Can you do the same for the Alfa? I have a multimeter, is there a way to check the alternator while running?
Trying to start the drive to Ft. Lauderdale by mid morning so I'm looking for help tonight.
Thanks artart

**papajam** · #2 (**permalink**) 07-03-2003, 05:17 AM

Disconnecting the battery to check the charging system is, unfortunately, a common practice. The battery acts like a capacitor. If disconnected, wild voltage spikes can occur that can burn out kinds of electrical stuff; light bulbs, computers, etc. A volt and/or ammeter is the most accurate, and safe, way to check the charging system when the engine is running.

First thing I'd check is the fuses (usually #6, but depends on the year). Make sure that they are clean and tight. Then disconnect the battery (negative side first), and check the connections at the alternator and regulator. If the alt light still glows, then the alt or reg may have been damaged.

Good luck!!

artart · #3 (**permalink**) 07-03-2003, 06:15 AM

Checked with a volt meter, getting about 13.6 with all accessories off and 13.3 with them on, (radio, hi beams, wipers....nothing else works and who cares about a fan) so I'm going to try the 350 miles (Jax to Ft. Lauderdale) around 10AM Got a case of oil, new sparks, my tools, and a whole lot of hope...
Thanks Jim
artart

**papajam** · #4 (**permalink**) 07-03-2003, 06:25 AM

With those voltages, it would appear that the alt is working OK. I'd think the other stuff not working would be, again, dirty fuses or a power feed problem to the fusebox.

Enjoy the convention!!