Rangie alternator and rev counter

Hello everyone, my rev counter has never worked on my 85 classic, which is a real pain in the ass when your trying to set the idle speed on your carbs I can tell you!! I just realised the reason is that it appears to be for a 3.9 or defender. My understanding is that the white wire with a spade connection should plug into the back of the alternator for the rev counter?? I was wondering if there is anyway around this short of buying an origonal alternator?

cheers
stuart