Some time ago, well over a year, I needed a new alternator so checked with the usual suspects (Island4x4 and LRDirect) for a 120A AMR2938 for a GEMS and found one of them gave me the option of a Britpart or a Hella . Working on the principle that a dead alternator can stop the car, I ordered the Hella. Fitted it and checked that it was working by putting my meter across the battery and was pleased to see 14.4V. Many months later (recently), I had the ignition switched on but engine not running and after about 30 seconds the dash beeped at me and came up with Alternator Fault. I also noticed no picture of a battery on the dash (but with all the other warning lights that come on with the ignition, it's easy to not notice one that isn't there). But the alternator was still doing what it should and charging the battery at 14.4V. Checked with the Nanocom that the bulb hadn't blown and found that I could make it come on from within the BeCM Outputs menu.
Recently decided to do something about it in case it stopped working and didn't tell me about it. I'd got 3 alternators in the garage but had no idea if any were any good. One was a weird make I've never heard of, one was a 100A version and one was the desired 120A AMR2938. Tried connecting the thin Brown/Yellow wire to the D+ terminal with the alternator body grounded through the rocker cover, turned on the ignition and no picture of a battery on the dash, but there was if I grounded the wire. Concluded the regulator was dead so ordered one of these https://www.onlinecarparts.co.uk/hc-cargo-25072361.html. It arrived within a couple of days and although the box said HC Cargo, the label on the box said it was made by Robert Bosch.....
Fitted it to the dead alternator, bolted it onto the car and with just the D+ wire connected the battery light on the dash came on with the ignition. Went to connect the main power cable to the alternator and got a spark. That shouldn't happen unless one of the diodes in the alternator is short circuit and a quick check with the meter showed it was drawing 6A. Bugger. So took it off again, removed the new regulator and was about to put it back in the box to keep as a spare. Then had a thought. The Hella was sitting there looking at me and a closer look showed that although the label on it said Hella, it was actually a Magneti Marelli, identical to the one that I had just taken apart. So I pulled the cover off the back and found it had the same regulator in it. So fitted the new regulator to the 'Hella', fitted it to the car, turned the ignition on and was happy to see a battery warning light on the dash. Started the car and the battery was charging at 14.4V. At least now if I do have a problem with charging, I feel confident that I'll have a warning light on the dash to tell me about it.
But this isn't the end of it. Nigelbb has been here today as we needed to change one of his front wheel bearings. While he was here, we were playing with his new toy, the Carplay/Android display. While playing he had the ignition on and the dash beeped and came up with Alternator Fault and we noticed that he doesn't have a battery warning light either. He thinks the car has done it in all the 10 years he has owned it but had never noticed no battery warning light. What makes this more interesting is his car is a Thor so has a different alternator but it seems they also suffer the same problem. Interestingly, the only regulator I can find listed under the part numbers for both Thor alternators, are a Hitachi one. I always thought the Thor had a Bosch?