@Cracked
Congrats on the new meter, its in my wish list too
. Do inform us of its details like what it costs, fitting, availability, any pics.
I dont know about the wire codes of these meters but I know this much that RPM meter needs signal from the ignition system. The positive terminal of the coil is always ON (when the car is switched on & also when engine is running) so no signal on it but the negative terminal is actually the signal point which is activated by the signal generator through the ignitor in the distributor. So for that reason I think that the signal wire of the rpm should go on the negative of the Coil.
The +ve (Black/white) wire going to distributor is the same as the Coils so it will not do any good therefore I would not recommend you to experiment with the distributor wires as it could end in a burnt ignitor. Its very sensitive and there is no room for chance.
I think there is nothing wrong with the coil, it doesnt make any sense that RPMs are related to Coils output current.
The swift GTi came with 175/65 R13 as stock and I guess you are running 165/70 R12 so difference of around 15km/h at 100km/h is expected. Meter guys can calibrate it if its some thing else.