One for the brains trust please.

I have a 1994 CBR 600 F2 track bike, OEM instruments are all shot so I bought an LCD digital tacho speedo etc. off ebay like
LCD Digital Odometer Speedometer Tachometer Motorcycle With Blue Backlight CSU | eBay .

My question relates to the tacho connection, the OEM one used a varying DC signal from the ignition control unit, the new one needs pulses. The F3 did the same, I don't know about the F4.

The ignition control unit has a wire to the left coil, another to the right coil, and a common wire to both. I tried back probing the connector to find out which of those wires to tap into for RPM pulses, but the connector is so well made I can't get contact even with a slim wire. I could lift the tank and get directly onto the coils but that's a bit of a drag in the dark, if someone already knows the answer for me. My guess is the common one (black/white) but I want to play safe and not fry anything.

In return I can advise the community if anyone interested on all the pinout changes to connect one of these aftermarket ones to the 9 pin Molex connector, it's not plug and play with this bike.

TIA.