Sounds to me like you need to dig into the wiring a lil and find a possible power draw..
First things I do is go and clean and check all grounds especially for the ones for the EEC and the EEC / fuelpump relays which give issues after the internal diodes burn out..
Another area to look is the pickup module..When the rubber gets soft like a gummy bear or changes color heavily its time to change the pickup sensor and just because the distributor you say you have is sold by MSD its made in China and donned with chinese made internals and what makes them really hard to service is the facts that the gear is pressed on with way more force than needed and when reinstalling the gear an oven and a freezer will be needed.....
Most people spend roughly $100.00 for a machine shop to do it and when doing a distributor gear replacement right depends on getting the timing right or setting the timing 12* off due to the odd amount of distributor teeth and the rotor being in 2 different places at TDC with dist gear installed right and when installed 180* wrong because the reluctor wheels placement for the small tip will be registering 12* off causing issues with the injectors spraying on time or turning SEFI into a crude batch fire system. firing the injectors 12* out of sync with intake valve opening eventts..
And speaking of the reluctor wheel theres a certain width each tooth and space must be and the reluctor wheel they put in at MSD was way off on size and widths also airgaps that I had to swap in the wheel from my old OEM Ford distributor to get better accuracy for the PIP profile..
And speaking of the reluctor wheel theres a certain width each tooth and space must be and the reluctor wheel they put in at MSD was way off on size and widths also airgaps that I had to swap in the wheel from my old OEM Ford distributor to get better accuracy for the PIP profile..
Look at the pictures of the gear below and how the rollpin lines up to the teeth on both sides..
When I had issues similar to yours besides the ignition switch the thrust plate in another engine had too much slack causing excessive cam walk which worn out the bronze bushing on the lower part of the distributor causing the shaft to short to ground causing havoc for the TFI module the coil and the ECU.
I start to check for wiring issues by doing a wire wiggle test while the engine is idling....If the engine changes pitch or stalls while wiggling the wires in a certain area will pinpoint the area of issue...
As explained above when I had the issue with one of my vehicles the ignition switch went bad and overheated after the alternator started running high and erratic which caused the ignition switch to heat up then break its seal and separate until it cooled but was slowly burning up too.....
Good Luck