Scooterotica

Fitted one of these years ago to a V90 that would not stop blowing the brake light bulb. I think a "zenor diode" turns excess voltage into heat then out into the frame. The one in the link has a matching heatsink too.

http://www.vehicle-wiring-products.eu/V ... /elecs.php

Before putting a band-aid on I'd try to find out what the problem is.
Is the lamp blowing instantly when you rev it high (too high voltage) or just frequently during riding (poor connection). The brake light is on it's own circuit so no other lamp will affect it, but if the brake light coil is producing too much power, due to engine tuning, the other coils are going to produce too much also and you'll have trouble with them.
If no engine mods have been done, and all lights are over bright, check that you haven't fitted a DC junction box by mistake.

Thanks for the replies, I'll check more things out. I'm pretty sure it's the original stator. This morning I managed to pick up a Lucas Clipper Diode with the heat sink, cost me a fiver from a motorbike car boot sale. How do I put it into the circuit?

the diode and heat sink is bolted to the rear mudguard- you then take a wire from the central terminal of the diode to the black wire from the rear light set up.

A 12v rear S&T lamp seems to be working. Is it possible to put the heat sink wire directly into the round black JB to control all the power?

The 12V S&T popped and someone even suggested a 24V! Anyway, I got the Lucas diode with heat sink connected to the pink wire and it's absolutely perfect. I bolted the diode and heat sink on just below the JB and it's looks really retro, very happy with the results.