I cannot find the Instrument cluster voltage regulator next to the speedometer or any where in that area. Out in the engine compartment close to the 3"X3" regular voltage reg. is a small similar looking little box to what is supposed to be in the cab, near the speedo. It is about 1&1/2" long X5/8" thick X 1" wide. There are 3 prongs coming out of it. there is one, mmm, 1/4" self tapping screw holding. Thank you fellow/gal slick 60's enthusists, cheers, Pete

 

That sounds like the relay - for the horn, on the inner fender apron. The constant voltage regulator "should" be installed on the back of the speedo meter ? Dunno. Not sure for 65s though.