As the title says, I'm hooking up a rpm switch to operate a relay. I am using this on a 88 NA. I have everything hooked up correctly, but can't seem to get it to operate. I have the input power tapped into a switchable 12v source. The black wire is grounded properly. I have the white wire (tach input) tapped into the yellow/blue bullet connection at the rear coil pack. I am using the yellow wire (activation to ground) connected to the correct relay post. The rpm module has two wire loops, red and blue for mode of operation. I have the red loop cut so the unit thinks it is running on a 6 cyl. This unit takes the rpm selectable plug in chips. I have the 4200 rpm chip installed. I can ground out the yellow lead and the relay operates correctly. For some reason, I am not receiving a grounding signal from the rpm box. So where did I go wrong? Any suggestions will be appreciated.

 

Never mind, I got this one figured out. The rpm switch can be configured to run an 8,6 or4 cyl. If connected to a rotary ignition, it is looking at a tach pulse configured for 3 fires per rev.



SO, if the rpm switch is set up to activate at 5000 rpm;

Configured as a 8 cyl., a rotary engine would have to run at 13,333 rpm to activate the switch.

Configured as a 6 cyl., a rotary engine would have to run at 10,000 rpm to activate the switch.

Configured as a 4 cyl., a rotary engine would have to run at 6,666 rpm to activate the switch.



So, if using an MSD rpm switch, run it as a 4 cyl. and calculate your target rpm by using a factor of 1.333. So if you need a trigger point of 5000 rpm, set the unit up to trigger at 3750 rpm.

 

Set it as a four cylinder. Rotaries have a four-cylinder firing rate (2 per revolution).

 

where does the grey wire go i have msd 6a part# 2501.



goes to the tach out i know but could i put it to the black wire, that comes from the L coil and seems to just end?