My V6 tacho seems to be over reading and I was wondering how you adjust them (if at all).
Spring tension? Adjustment screw?  Any thoughts?
 
And also, in doing some reading on the subject, Ive found multiple references to the double loop of the induction wire thru the block on the back of the tacho.  Why a double loop ?  I understand about the pulse principle involved here.
 
I've only ever seen a single white +ve feed wire passed under the block (i.e. no loop).
This doesn't mean it shouldn't be doubled.  As with all old cars, they get taken apart and sometime's not put back together properly.
I'm ready to be educated on this topic.  
 
Thanks in advance.
 

From my experience, these dedicated Tachos are only repairable by Instrument Technicians such as
 
Ringwood Speedometer ServiceGeneral Instruments - Mitcham, VIC693 Whitehorse Rd, Mitcham VIC 3132
 
Theyve been doing it a long time and they fixed my RWC Brake Decelerometer 15 years ago and it hasnt missed a beat
 
Im sure theyre not alone, as Dr Google may prove

A couple of old threads that may help
 
http://www.classic-ford.org/cfp/tm.aspx?m=67057
 
http://www.classic-ford.org/cfp/tm.aspx?m=45879

Thanks ....