Dear Tim;
That's right.
You need to raise the source voltage to 12V. This can be done by adding a small 6V battery in 'series' to the tach circuit.
You may need a diode (one way valve) in between the two.
Now I'm not sure on the values of the parts & you will have to charge the second battery every now/then as well. Your 6V system charges @ 7.7. I stated "lantern bat." but they are dry cells & a lead/acid motorcycle one may be needed.
An 'isolated' 12V source will work also as Mike sugested.
You could check with Jason Sternhagen #287 on all of the fine points.
This will work until you find one on e-bay or the local 'swap meet'.
Good luck, John M.....
