Twas said...

The circuitry at the back of the speedometer is for the dynamic oil
pressure circuit board, which is inside the speedometer casing.

Hmmm, I thought the oil pressure circutry used the engine speed as a trigger
parameter taken from the tachometer drive circuitry.

I'll have to take a look.  The Magnetic pickup that feeds the cruise control
to determine vehicle speed plugs into the back of the speedo but that's all
I recall of speedo electrics.