Old Airguide tachometer transmitter schematics.

["Merc"ulies]

Due to the availibility inbalance between older Airguide tachometers, and the transmitter units that work with them, I am asking if someone has or knows where to find the internal schematic diagrams of these transmitter units. If I knew the specs, I would be able to build one for my Airguide tach, model 653. (Wanting to use for a 4 Cyl., 2 Cycle Mercury Mark 30 outboard.) Does anyone know where I should look to find this information?