On my 1991 Mk1, I seem to have a charging problem: When I start start the engine, the alternator doesn’t seem to charge properly until the engine reaches about 3,000rpm for the first time…At this point, the lights go brighter, the heater fan speeds up, wipers run faster etc…This isn’t good, as it’s forcing me to allow the engine to rev that high before I’m really happy that it’s warm enough, and on one occasion I started the car, allowed it to idle for several minutes while I answered a phone call, then realising I’d forgotten something, switched the car off for a minute, only to find that there wasn’t enough power in the battery to turn the car over and restart it!
I’m assuming that there is some sort of voltage regulator that’s at fault (I’m rubbish with electrics!), but does anybody know if it’s integral with the alternator, or a seperate unit?
The regulator and brushes are individual parts in the alternator according to the Mk1 workshop manual and in theory can be replaced. Not sure where you would get replacement parts though (Mazda franchised dealer perhaps?).
UPDATE! My local motor factors has a sister company that remanufactures alternators and starter motors. They list the VR separately at a price of £17.60 (presumably + VAT). Like a lot of the electrical components on the MX5 it is a Mitsubishi part and therefore may be commonly available elsewhere. Looking at some of the cross references, the brushes appear to be available for £2.96.
It looks as though the regulator is part of the brush holder assembly. The rectifier diode pack is a separate component.