Sometime I buy parts from this place called sherco auto parts. This weeks flyer has 12v to 6v reducers in it. I know there is always some discussion about it so I attached a link. I have used the company multiple times with no problems but have no experience with that particular part. http://www.sherco-auto.com/Merchant2/merchant.mvc?Screen=PROD&Product_Code=GEN45311&Category_Code=E
This type of reducer cannot be used with a radio or with gauges it also has to be mounted in an area away from anything that could be damaged by heat the insulators become very hot when under load.In many cases they were used for heater blowers luckily there are 12 volt motors that will bolt in our Fords for about the cost of the reducer.