The Charging System Warning Light was not coming on - I presumed a blown bulb - but the garage said no, it was fine and they thought the problem lay with the regulator (they've had this before) or possibly the wiring loom. They couldn't readily test further without charging for investigation (maybe one hour = £49.94) and advised that the probability was a new alternator being required at a fitted cost of approx £245-250. They also suggested that if I left it as it is, the charging circuit may be operating inefficiently although it seems OK. Any comments? (11/99)

I'll dig out a circuit diagram for the charging side and try and suggest other tests for the charging light problem. I'd certainly consider buying an alternator yourself and getting a non-Mazda garage to fit it. That price sounds ultra-high. However, I don't know what's involved in an alternator swap on an MX5 but it seems well burried and it may be best to swap it from below. If everything is charging I'd leave the alternator alone though. (11/99)

It is just possible that a diode, located between the warning light and the alternator has failed. Ground the 'L' terminal (the upper one of two terminals together on the side of the alternator) - but NOT with the engine running. If the charge light works - the diode is OK, otherwise it could be replaced - sorry I don't know where it is, but it probably doesn't matter. Otherwise the problem is likely to be the switch transistor within the IC regulator. I'm afraid the practical cure for that is a new regulator. I'd look in Yellow Pages for an alternator specialist - I can recommend one if you're within range of Stockport. Don't panic though if it's charging OK - but you won't get any warning of future faults. (11/99)

alternators work or don't .. as long as the wiring is correct .. I have rebuilt a couple but the brushes on the last one beat me and they turn down the comutator on reconing them .. and I don't begrudge a recon alternator for 70 GBP after 140k miles (except where it was steamed to death by a blown cylinder head gasket). (11/99)

Thanks for the replies - the concensus was to take it to an auto electrics specialist which I've not yet had the chance to do. However the battery's gone flat again after only 9 days in the garage (admittedly with the alarm left on) so maybe what the dealer suggested is correct. Anyway rather than just charge the battery insitu I decided to take it out so that I could investigate the following point in more detail. (12/99)