This is courtesy of Unclemunz for those with the msd window switch and the zex kit using a tps switch.
If you Have a Zex Kit and a window switch READ THIS
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Many of you may already know this, but I didn't so I thought I'd share.
The window switch that I was upgrading to (Digital MSD, very commonly used) is set up to send a ground within the target RPM range. Using standard solenoids, it is of no consequence whether the 12v or ground is switched. However, when the Zex nitrous controller loses ground and retains power, it will draw a weak ground through the TPS connection while the car is at idle causing a rough, fluctuating idle.
You must use a relay to supply 12volts instead of ground from the MSD box.
sorry for the cheesy diagram. Someone with access to a paint program can probably do better.
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```````````````````````````````(pin 30)/``12 volt source````````````````````````````
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````````````````````````````````````/``````````````````````````````````````````` `````````````````````````(pin 85)```/`````(pin 86)`````````````````````````````````
________________________________ [relay]________________________``````````````````
`yellow wire from MSD switch``````````\`````````````````12 volt source````````````````
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````````````````````````````(pin 87a) \ power wire for ZEX box``````````````````````
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