Instructions I see use the grey TACH wire.
PROGRAMMING THE REV LIMITA tachometer is required to set the rev limit. The limit is programmed by running the engine at half the desired rpm, then momentarily grounding the Gray tach output wire from the MSD. A Gray jumper wire is supplied to connect to the tach with another tee-splice coming off to use for programming. A switch may also be installed to ease adjustments of the limiter (Figure 15). The default rpm limit is 10,000 rpm and the limit is adjustable from 2,000 - over 10,000 rpm.. 1. Start the engine and bring the rpm to half the desired rev limit (for a 6,000 rpm limit, raise and hold the rpm to 3,000). 2. While holding the rpm steady, short the Gray tach wire to ground for approximately one second. Note that the tach will go to zero while grounded. 3. The tach will now display the programmed rev limit amount for two seconds. If this value does not register on the tach, repeat the procedure and try a different ground source. 4. To confirm the rev limit value, turn the ignition key to the On position (without cranking the engine). The rev limit value will be displayed for two seconds on the tachometer. Note: This rpm confirmation only displays when the Gray wire is being used to trigger the tachometer.
