Bottom (black) relay. You can get one from Maplins or similar. It's just a standard automotive relay,
I bought a new HRW switch Mk1 and relay and when i came to fit the relay there was already one in the slot but the 25 amp fuse had been removed (or was never there in the first place!) I fitted my new relay in case the existing one was duff. Switching the new switch on the light did not display and there was no power to the rear connector either, after a lot of searching i discovered the rear window circuit is only powered with the engine running
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