1974 1.8 L-Jet. Pertronix 1847V. No spark when cranking over the engine. I do get one spark on a plug when I turn the key switch off and the rotor is in the correct position to spark that particular plug. What to check?

New cap and rotor.
Bosch blue coil.

Update. It looks like the pertonix sensor is to high on the distributor mounting plate.

Your missing something in your distributor. Points and condenser.

You missed the part about having a Pertronix.

Well, no. I did not, but you missed my attempt at humor! His pertronics is probably toast. He needs to install points and see if it runs.

rotor maybe---or timing is just out

Does your timing light flash when you test each plug wire while cranking?

Had the same issue a couple years ago. Every time it sporadically sparked it sounded like I was shooting ducks in my garage. Neighbors LOVED it! Failing module from what I could tell. Ended up putting the good ol' mechanical stuff back in and drove down the road fine after 5 minutes of reinstalling and setting timing.

I have found one of the most important things you need when converting from mechanical points to a Pertronics............A SPARE PERTRONICS SET-UP.

Make sure the petronix magnet is seated correctly on the rotor. I had a similar problem shortly after original install, it was that the magnet was not fully seated correctly on the rotor.

They have a trouble shooting guide on their website if you want to check the unit. I've had one set in for 5+ years w/o any problems.