Mercrusier voltage drop

[tfitz717]

I have a 96 Merc i/o 7.4 carb eng w/tb V dist. At idle volt meter shows approx
12.5 volts. As rpm increase voltage drops to abot 10 v. Boat has 2 stations and both guages read about the same. Eng starts easily. Tried new alternator
with same problem. Needles on volt meters are very shakey. Thanks for any
sugestions.

 

[Don S]

Re: Mercrusier voltage drop

You need a new alternator.

 

[achris]

Re: Mercrusier voltage drop

Check the voltage at the battery with a good quality multimeter, preferably a Fluke. If the voltage is the same as you see on the gauge, then check it at the back of the alternator.

If you have the same at the alternator as the battery (and the gauge) then you have a faulty alternator. (Yes, a new one can be faulty too)

If the voltage is good at the alternator and bad at the battery, then start doing some wire chasing....

Chris......

Edit: Don, Do you ever sleep???

 

[Don S]

Re: Mercrusier voltage drop

Edit: Don, Do you ever sleep???

It's not even 4:30 in the afternoon yet, much to early for sleep.

 

[achris]

Re: Mercrusier voltage drop

It's not even 4:30 in the afternoon yet, much to early for sleep.

Sorry, It's daylight here and I just assumed that when I have daytime, you'd have night-time....


Chris.......

 

[chiefalen]

Re: Mercrusier voltage drop

Take both alternators and battery to auto zone and have them test them.

Then for sure we will know whats what.

Won't cost nothing, post back don't buy anything.

 

[tfitz717]

Re: Mercrusier voltage drop

Thanks guy's. I will reorder alternator and check it out one more time.

 

[HT32BSX115]

Re: Mercrusier voltage drop

Thanks guy's. I will reorder alternator and check it out one more time.

Well, before you order a new one check the voltage with a separate Independent voltmeter like Chris suggested (I have a Fluke 187!) Check all voltages from the negative post on the battery to that connection.

And while you're doing it check all the ground points, remove and replace all the fuses and check all of those connections too (if they're the ATO/ATC type fuses it's not uncommon to have corrosion on the fuse connections too).


Cheers,

Rick