alternator replacement; hard to do? expensive part?

[blackknife]

I just started having trouble with my cranking battery. I've ruled out the battery (I think) but the motor seems to not charge the cranking battery when I run it. in fact if I start the motor more than 3-4 times it kills the battery. The battery definitely takes a charge no problem, so I thought maybe my alternator is bad? any thoughts or advise? this all started happening the day after I replaced the Lowrance LMS 480 at the console with a Humminbird 797. is there anything under the console I could have screwed up that would cause this?

2002 150 VMAX fuel injected

[JUST-IN-TIME]

got a handheld volt meter??

[blackknife]

yes....it's how I've been checking voltage on my battery.

[JUST-IN-TIME]

well put it on a/c volts
put the leads on the battery
start motor, rev it up a little
if u see more than .8V you got a bad reg/rectifier

then u can switch it over to d/c volts to see voltage also

[blackknife]

I found that while installing the combiner I must have forgotten to run a wire from the cranking battery negative to the trolling battery #1 negative, so I'm thinking that maybe this had something to do with it? I'll have to check the output voltage from the motor as you suggested, I'm just really hoping that's not the problem.

the wire I forgot to install is the one with the 2 green arrows in the pic below. I've had this charging system installed for a couple of months, and although I killed the battery once by leaving the power switch, and ignition key on overnight, I've never had it die on me while on the water, but I don't think I've ever started the motor more than 4 times while I was on the water. (VERY small lakes in RI!)





Modified by blackknife at 4:58 PM 8/24/2008

[Rich Z]

W T H?????
Do what he said!