Help! 12v & 6v T2 electrics...

[Tim-D]

Calling all those clever with archaic electrics.... problem - a '63 VW T2 van - specifically the wiper motor - this van was originally wired up on 6v but has been converted to 12v and as if it makes a difference the dynamo has made way for an alternator. The problem being that the wiper motor is now working so ferociously that the linkages all pop apart - the probability is that the 6v wiper motor is still fitted - hence taking double the volts (it has been smelling a bit!) So my question is, being a cheapskate - can anyone advise using bits & bobs available from for example maplins how to put together a resistor circuit to get the voltage back down????? (already considered new motor but if it can be done for pennies so much the better)
Cheers all.....