Here's the diagram for stock 1200 tacho:
Tacho wiring diagramThe two signal wires are connected in series to the coil ballast resistor + side (not directly to the coil) , at least according to my wiring diagrams. These wires are both black/white. One goes to IGN fuse, the other to the ballast resistor + side. In other words, the tachometer is between the IGN switch and the resistor + side. Don't wire it in between the START wire and coil + or it won't start.
The other two wires should be for the light:
black - ground.
red/yellow - light power
green/white loop - connect to the black/white IGN wires.
My 1975 B210 wiring diagram also shows the B210 tach connected to a 'black/white' wire.
On the other hand, most tachs are not connected to the coil + wire. The "signal" is on the coil - side -- it signals both the coil and the tachometer. My Toyota Celica tach is wired this way to the A12, and the B310 elec. ignition even has a special tach wire wired into the coil '-' wire harness. The aftermarket tachometers I've used are also this way.
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Transfer
