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Old 09-17-2013, 10:56 AM
bgw15 bgw15 is offline
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Join Date: Sep 2013
Boat: 1984 Mastercraft
Location: northeast
Posts: 2
1984 Motorola 788b alternator

Hi All,

New to forum and just bought my first Mastercraft 1984 SS. I took it out the other day and was going for a slow cruise and pulled up to the dock and was just idling and boat stopped. I tested the battery with boat off and it was about 12.4 and then started the boat again and it was 12.6 so I am thinking I need a new alternator.

I searched thru the forums and saw a couple of threads about similar issues but none mentioned which replacement alternator to get. I can not find a replacement for the Motorola 788b alternator when searching the internet.

any help would be appreciated. If you don't think it is the alternator also please let me know.
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Old 09-17-2013, 11:59 AM
thatsmrmastercraft's Avatar
thatsmrmastercraft thatsmrmastercraft is offline
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Join Date: Sep 2008
Boat: 1977 Stars & Stripes
Location: St. Paul, MN
Posts: 18,545
I am of no help on a replacement alternator, however, many of the older alternators needed to get above 1500 RPMs to excite the alternator field and start charging. One of the first time I took my boat out I had previously only run it at idle in the driveway, then idles through a no wake zone and idled across the lake. Didn't want to start once we were ready to ski. Easy to check. Might also get your battery tested to eliminate it as a possible source.

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Old 09-17-2013, 12:18 PM
keith3613 keith3613 is offline
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Join Date: Aug 2004
Posts: 117
I also have a 1984 S&S that I bought new in 1984. The alternator can be rebuilt by an alternator shop.
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Old 09-17-2013, 01:18 PM
bgw15 bgw15 is offline
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Join Date: Sep 2013
Boat: 1984 Mastercraft
Location: northeast
Posts: 2
thatsMrMastercraft, thanks for the info. I did go above 1500RPM's still no higher than 12.6

I will call around to see if DB Electrical or a local store knows of a replacement. If not I will go with Keith3613 and look for someone to rebuild.
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