I wanted an indication when MDS is active (running on 4 cylinders.), partly just for interest, but also so I can see the behaviour, and maybe change my behaviour to make the most of it.

So I tapped an LED into one of the MDS solenoid lines (using a fuse just to be double-safe, it’d suck to short it out somewhere (like passing through the firewall.) and risk messing with the module. Then just ’mounted’ the LED within the ScanGauge which already sits on the dash anyway.

Having the ScanGauge itself monitor MDS state would be better, but until someone figures out the PID for the X-Guage, this is probably the next best thing :-)