Posted by Sherman in Idaho [72.47.153.64] on Friday, May 08, 2015 at 15:43:45 :
In Reply to: Alternator Problem Question posted by Paul(in NY) [12.64.186.119] on Friday, May 08, 2015 at 15:13:04 :
Definitely a possibility, but before I'd spring for a new alternator I'd do a few more tests. First would be to check the voltages at the alternator output lead, battery + POST and battery - POST relative to frame ground under heavy load conditions. A bad connection will cause the same symptom as a weak alternator. Personally I prefer to actually FIND the bad connection via voltage measurements (if there is one) rather than remove, scrape, and brush each and every connection and keep repeating that in the hope that it fixes it. I had a weird problem on one rig (weak charging) that turned out to be a poor connection between the alternator bracket and the engine block. We normally take that for granted, but there was enough paint and dirt on it that it dropped about a volt under load, which makes the difference between charging a battery completely versus barely. The best test is to put the voltmeter on the most sensitive range and check for voltage drop between every pair of things that should be connected -- alt housing to block, block to frame, bat cable to bat post, alt output stud to alt cable, etc. Expect tens of millivolts, but if you find hundreds of millivolts, clean it up. If the actual alternator output AT the alternator itself (output post to case) is dropping to 12.1 under load, then yes, the alternator itself is probably bad.
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