Low Voltage? Intermitent Beeps? Merc 150 4S

[JS!]

Got out on the bay today with a new to me 150 4S. New Interstate battery freshly installed, all wires tight - I believe less than 100 hours on a 2015 motor S# 2B142XXX

Noticed the volt guage was a little low, as was the volt reading on my Garmin graph. On a long run, noticed when I hit the trim button at cruise speed, tachomether went to zero until i let off the trim button. Then i got an engine alarm, intermittant.......on, off, on. Shut off and checked oil - all OK. Now voltage too low to start. jumped with cables from one of my TM batteries. Ran fine at idle and up to less than plane speed. Then anything above idle was rough, Then motor just died. Volt guage was less than 10v.

Alternator?

Battery is brand new.

Removed alternator and brought to AutoZone for testing but they did not have the proper wiring plug to test it. I live in an area where there are almost no boat mechanics. A replacement is $300

What else could it be? There are no loose connections, all of the wiring is solid, I checked it all out. The motor is like new. Fusible link I will check tomorrow with an ohm meter, no reason for it to have blown, battery was hooked up right.

**Noticed low voltage since I bought it on both the dash gauge and Garmin unit.....thought gauge was bad....guess I was wrong.

Any help beyond alternator, fusible link and poor connections appreciated!

[EuropeanAM]

Check the voltage at the large output terminal, KEY ON, ENGINE OFF.

Then check the voltage at the large output terminal, ENGINE IDLING.

[JS!]

just did that, Voltage is slightly lower with the engine idling. Ramped the RPMs up to 1000 and same result.

[EuropeanAM]

At the small connector (unplugged): Check for 12V+ power on both wires, with key "on".

Results match: Replace alternator.

[JS!]

OK just did that - both wires had the exact voltage with key ON - 12.37V which is pretty much the same voltage I got earlier at the output terminal while running and with engine off, key on.

Just ordered an OEM alternator from my local Merc shop. Thanks for the help!

[EuropeanAM]

[JS!]

Went and picked up the alternator today. Removed the old one, installed the new one, fresh blue Loctite on bolts, torqued to factory specs, made sure fusible link connector to alternator was clean torqued that nut down to specs and inspected the belt. Re-installed the freshly charged battery and fired it up. 14.5V while running. All is good again.

I also installed a VesselView Mobile unit today. Now I will know a little more about what is happening. Also confirmed the hours at 95 which is about what the seller estimated but was not sure. Not too bad for a 2015 motor.

Thanks again for the help, saved me paying shop hours for diagnosis and a pretty simple alternator swap.

[SilverFox579]

I'd have the old alternator rebuilt locally and then set aside for a spare.

[Table Rock 1]

Good info..

[JS!]

Yes, I learned a lot about outboards on this one. Like I said before, I am a total newbee to outboards. Been boating since my friend's grandfather took us out as young teens and I always paid attention but this is my first outboard. I now know how important the electrical ssystem is in a modern outboard - it is a major componenet, Which us why I opted for an OEM alternator at about $350 from my local Merc dealer as opposed to an $88 rebuilt alternator on <EDIT- SEE ANNOUNCEMENTS>

I also installed the VesselView Mobile this week so I know what is happening in my motor and can double-check my gauges. I did not trust my voltage gauge and I should have - now I have another source to verify. And I know that if my battery is insufficently charged, bad things will happen. Not good when you are in a huge body of water with only one other boat within miles.

Thanks BBC Boards! Learning every day.