https://item.taobao.com/item.htm?id=536139476392 had good tips.
Basics in that url =
Rpm signal can gotten from multiple locations. Find the least inference 1 by ur self (or shielded that wire)
1. the electronic rpm gauge line (some model had this, the signal is best)
2. IGN coil in (If don't had
1 recommend connects to here)
3. CDI's out
4. CDI's IN
5. Trigger's out
6. ECU's out...