Failed 40 Amp Upgrade

Joined
Sep 24, 2025
Messages
26
Age
25
Location
Wisconsin
Bike
1992 ST1100
After a successful alt. upgrade performed over last winter, I have put about 3k miles on the new alternator, and I was left stalled on my way to work just yesterday. After getting the bike home after work last night, I performed the basic tests for an alternator and found that the battery was receiving no charge.

I'm hoping it may just be a fault in my wiring rather than a bad 40 Amper as I don't know that I could put myself through another alt. replacement. Does anyone have any ideas on where to start looking or a test procedure to eliminate the fear of a bad alt or common failure points in the upgraded harness system?

This is a real heart wrencher at the moment as riding weather is more and more upon us, and I was already enjoying my ST more and more than I was last year.

Thanks,
Jonny
 

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These alts aren't known to fail and they're much simpler than the oil-cooled 28-amp units. Best you can do is test for output (once you get it going) and also test the regulator and continuity to the battery. Also check your main wiring plug next to battery for signs of overheating. If so, Search for the "red plug" fix.
 
Connections! Did you sandwich the connector at the new alt’s ‘stud’ between two nuts? Checking the fuse of course. Others will be along with more advice….

John
 
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