[911tracker85]

I replied to another similar thread.

in my case my coil failed. checked a LOT of stuff, but not the coil at first because I could not find my test light AND it was NEW.

I agree with notmyscreenname's post. the way I found my coil issue was to connect test light to the 'trigger lead' (just cant recall what that control connection is called) on the coil.

as he noted, with key on, you can use a volt meter to verify +12v on both leads to the coil. when cranking the engine, the voltage on the control lead should toggle. so with the test light connected to that control lead, if cranking does not cause the test light to flicker, you are not getting signals from the DME to fire the coil, so no spark. the toggling is fast enough I am not sure you will see it register on a volt meter, but using a test light worked for me as I was able to see it flicker, but nothing out of the coil lead to the distributor.

if you do not see +12V on both, and do not see the voltage toggle on the control lead when cranking, there can be many things that can cause that such as DME, crank/speed sensors, wiring harness, etc.

PS. trying to test the signals from the crank/speed sensors needs a O-scope. ironically I chased that first as my tach was not bouncing as referenced. turns out my tach just did not work. I also put my DME into a friend's car to verify it was good.

in my case I was working on an 86 951. not sure about other issues with an early NA.

good luck