318 stalling while driving

Yeah if it's just dying then I'd be looking at electrical. As stated make sure the ECU is well grounded. I run a wire to a good ground to one of the mounting screws.

Also, as dano said; possibly you are losing voltage to ignition from bad ignition switch / bulkhead connector.

Quickest thing to try is when it is not starting, check for spark and then start measuring voltage at ballast etc with key in "run position"