Alternator regulator swap Motorola 9AR2637P

 I was also under the impression that the internal regulators fitted in the alternator  couldn't be changed without changing the complete unit. However, the regulator can be replaced; its a small finned box on the rear of the alternator. 

At first it was hard to track down the necessary parts. The parts manual confirms that Lotus used two alternators in the Excel- mine being the earlier type. However, beyond stating that they are Motorola 70amp units there are no details on either. I couldn't see an alternator spec label on mine but found it hidden beneath; and this states that I have a type 9AR2637P of specification 14V, 70A, SEM45, AN8J (?). I don't know what many of these later designations mean' Motorola itself seems to be known as Valeo now.

Label- a little faded

A second shot of label

The regulator is the finned box located at the rear of the alternator.

Rear view of alternator- regulator unit

The regulator has been used in many models of alternator and car. Equivalents are manufactured by many firms- or rather "were" as they seem to be very scarce nowadays. Some selected regulator part numbers for my alternator are given below:
Lucas UCB500, 21229047, 21229114, 21229141; Motorcraft EGR305; Bosch F 042 320 290; Hella 5DR 004 241-041; Ford 5018316, 6048270, 77BB10316 (and ditto postfixed A and AA). Of these I could only find branded units by Hella and these were very expensive. Cheaper replacements  are available from a variety of suppliers at around £10 but these are smooth cased lacking fins. Further, their actual manufacturer isn't clear. However, this is what I can get so I ordered one of the these from VECO.

This arrived in due course and turns out to be branded "Cargo" and made in China.

Swap was straightforward.