Thanks for that, I had remembererd that the ECU was "Ignition triggererd" (I used to have a jag V12 which used the same system) but forgotton that it was via a separate set of contacts. But, in this case it is always the same output that drops out. Not sure how a "Reed switch" (as I recall them being described) problem might consistantly fail only one output. But it is something else for me to connect the pico to when I get back to it.