You got to get back to basic checks first:
1-what's the voltage on the alt post?
2-40a, if it's an inductive ammeter and it's placed to close to the alt, the
magnetic field present may confuse your reading.
3-do a voltage drop test on your alt (+) wire and (-)wire on the block.
4- good voltage should be around the 14v +/- .4v


wrote in message
ups.com...
I have an 84 Wellcraft 200 elite w/a 260HP merc. Symptoms are as
follows:
- Battery never charges while under way after a day on water. Has died
sometimes but I take a spare. Still, no fun.
- Dash voltmeter never reads more than 11V --usually less. I recharge
bttys before each trip. 11V or less even w/new battery.
- Have to retighten alternator belt often. Rubber dust on engine hood
says it's getting ground down. Running out of room on adjustable bar
for Alt.

Here's what I've done so far:
- Brand new marine battery, new Alt and Starter last year.
- Brush corrosion from posts, cables, wires.

While idling, Alt reads 40A on back w/ multimeter. No juice getting to
btty, tho. Someone said maybe Alt pulley is wrong size (tho I gave old
one to match at Alt shop). Said maybe a '9 series' pulley to match belt
#9440. Alt shop guy never heard of it tho. How crucial is belt brand?
Have matched size of new one from auto parts store to old one.

Any ideas much appreciated! THANKS. -- STB