Hi Art.

I've never bumped into one of those external battery temp sensors. They would have been used to keep the charging voltage going too high so as not to cook a battery and shorten its life. Those may well have been in the days before sealed maintenanzce free batteries became the norm. The regulators with internal temp sensors would have taken longer to notice a hot engine compartment, especially if located on the intake side of the engine.

They're not shown in the aftermarket 240 wiring diagrams I have, nor in the charging circuit sections of the later 700/900 green manuals I have. However, in the master wiring sheet at the back of the 1989 740 green manual I have, it is shown as an optional component living under the battery (comp 1 at coord B1 on the sheet).

These would have had external spade connectors on the regulator and I don't ever recall seeing that kind of thing in North American Volvo parts listings.

I do recall seeing mention of these external temp sensors in some 240 alternator charging circuit diagrams and discussions in other forums. It was a button shaped thing under the battery tray, early/mid 1980s as I recall.

I just found a 2019 thread over on Tbricks that mentioned them (referencing a TWC hybrid regulator) and you remarked not having seen one. It's mentioned for 1985-1986 240s and that the regulators were troublesome. Someone incorrectly mentioned that the battery temp sensor was for the ECU (which we know the LH ECUs don't use, only the block temp sensor, and they have no control over the charging circuit).

I now see in Volvo parts schematics mention of an alternator temp sender in some of the old 240 55A Bosch alternators in the carb'd B200/B230 engines (1979-on), so that would be non-North American market, which makes sense. It's not shown as a separate part, just noted in the alternator description that there's a sender, so those alts may have been those using an external regulator with a temp signal from the alternator?

I do see mention of a battery temp sensor used in some of the later Volvo FWD/AWD models. I'm not sure if that's directly connected to the alternator or ECU.
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Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now