I had exactly the same problem this year, I could not find 1 for love nor money - i have replaced both my alts. with A127-55 (as found on rover Montegoes <sp?>, i belive) and i have junked all the regulors etc.
There is a web site which details how to add extra diodes to the alts. to get round the problem of the 3aw relay search this site to find it (sorry i cannot remember the site...)
Or
Just live with the lack of light, with the lucas system the alt. is still has field coil active at ign. live with out the light on, just keep an eye on your amp meter / volt meter to make sure its all working ok.
IMHO, i would just replace it. modern alts. are far better, the A127's on my boat do far better than the old relay 1s
<hr width=100% size=1>Thanks
Leyton
(EXTAR Solutions - Software that works for you)