3220 hours on the machine The alternator stopped charging about 9 months ago. I called CAT and they wanted $611 for a replacement alternator!! I took the existing unit to a local rebuilder and $50 later, she was charging again. Fast forward to 2 weeks ago and it is not charging again. Ok, time to find a new one. Call around and find what seems to be a suitable replacement for $311. It is supposed to be the same unit, but 105amp not the stock 90amp. CAT tech even confirmed that the new PN was an alternate for machines with a cab. My guy puts it in and the back is a little different. The harness has a yellow and green wire. The alternator has a green and black wire. He figures green to green and black to yellow. It still doesn't charge. Even swapping the wires, it doesn't charge. It seems to be a Denso unit and seems to have an internal voltage regulator. Any assistance would be much appreciated! Thanks!
I'd start with the original rebuilt one that stopped charging, take it back to the rebuilder and see what he says. If he says it's working fine on the tester, then the problem is with the machine wiring and the new alternator won't work any better than the old alternator. In my limited experience, I haven't seen an external regulator on an alternator since the old ford pickups, and the alternator could be a Delco or a Denso, if there's only two wires (plus the big one)(and neither are grounds) then it should work.
I don't understand what the voltage regulator would have to do with it. Most alternators these days have an internal voltage regulator. The yellow wire in the machine harness should be hot with the key in the "ON" position. It comes via a resistor from the key switch and connects to the "D" terminal on the OEM alternator. The green wire in the machine harness should connect to the "W" terminal of the OEM alternator. It takes a signal to the electronic machine control - I assume to indicate that the alternator is charging.
A "W" terminal is usually(?) an AC tap for the tachometer (or computer or whatever in this case). I'd expect that to be a third small wire, but I'm lost.
I'm just reading from the schematic. The Machine control simply says "Alternator R terminal" with no indication what it actually does. Looking at the colour code of the schematic it is listed as part of the "engine control circuit" so I suspect it is a signal wire because other wires the same colour come from components such as the oil pressure sensor, inlet restriction sensor, fuel level sensor, etc.
I have been busy with other stuff and have not had a chance to be back at the machine to check on your suggestions. I am very grateful for your input and will post up as soon as I have a chance to further diagnose. Have a great weekend!
turned out to be a burnt resistor. took the CAT dealer over 3 hours to diagnose it. for a $16 part. hope this helps others.
have the same machine, thanks for the post.