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Quick update. I was able to buy a complete rebuilt unit from Pgh Ultramatic. So there will be no microcontroller project from me this time around. Thanks William, and everyone else who helped me out with this!
John

Good to hear. Hopefully your pressure switch is still present on the transmission and is working along with the relays because all those are unique to the PB operation and things you probably won't easily find except here in the US.

I got a new pressure switch, and I’ll have to look into the relays when I get back. I have family traveling in May, so getting relays later should be ok.

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Howard, it’s my understanding that the entire relay set can be replaced by a number of standard SPDT relays. I advised John accordingly if he has problems or missing relays, at least to get the system working. Of course the relays on his car will probably need to have the contacts and terminals cleaned to ensure reliable operation anyway. As with any older relay.

I did sell him a new pressure switch along with the unit, and advised to pick up some pipe fittings for it.

Spud,

The shift relay would need some figuring out if using after makey relays

Parking relay no problem with after market, I'm using one.

A good ground is a must..

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The auto park and start relays can be easily substituted with inexpensive cube relays so no big deal. A modern circuit breaker can also be easily found.

The shift relay is the more difficult item and could be done using cubes but much more work. To precisely duplicate the circuit in the existing relay would need 2 cube relays in parallel for each direction or else finding a couple of 12v DPST relays that can carry the high motor current and be a physical size where the pair could fit the existing space. For the resistor used to slow the one direction, I believe the resistance spec is in the Autolite SM but don't believe the wattage is mentioned. Not sure exactly how critical matching resistor specs would be for function but finding an exact substitute without buying a multitude of spares may not be as easy.

Another not as easy to replace item is the pressure switch but it could probably be duplicated too. The pressure spec is not given but SM says it opens between 5-8 mph. With the governor pressure listed as being between 11-14 psi at 13 mph, logic would say finding a switch with a pressure rating somewhere around 6 - 7 psi should work. If a 2 terminal isolated switch similar to the original couldn't be easily found, an idiot light oil pressure switch working another cube relay probably would do the job.

All in all, lots of work to mickey mouse a functional work around if the factory setup is not at hand. Based on the amount of difficulty people seem to have trying to figure out the factory electrical items, it might also be a good idea to leave a bottle of hair restorer or a gift certificate for a few days stay in a nice relaxing mental health spa for the next person who tries to figure out and fix the work around. That bit will be needed because undoubtedly any paperwork that might have been left explaining the mod will have been misplaced.

Here’s a schematic of that relay. It’s basically two SPST relays connected.

The resistor could just be measured and the maximum necessary wattage is determined by the simple formula V*V/R. The actual necessary wattage could probably be half of that, dependent on the manufacturer data sheet and resistor type, since the duty cycle is so low.

For the pressure switch, there are still many NOS ones between me, John Lauter, Patrician Ind., etc. as well as good used ones.

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Don't you mean "basically two DPST relays connected"? If you tried to do it with a single pole you would need to tie the two wires now going to separate contacts together and would essentially wind up wth a short because terminal 2 would would then connect to both sides and that tie would energize both directions at the same time. Two cube type SPST relays per side in parallel with commons connected together and going to ground would work or a DPST per side again with commons grounded together would too.

Oh right, DPST. The right would be, first circuit 1-5, second circuit 2-5, coil 4-5; arranged comparably on the left relay.

First circuit 1-5 is topologically the same as 1-2 but results in less current on the contacts.

Must diagrams I’ve seen show the auto-park disabled per a bulletin in one of the Service Counselors and even some reproduction harnesses are not worked for it. Personally I would prefer that any harness I use has it intact but that’s just me liking originality! Apparently it was problematic but the issues tended to be lack of understanding by the car owner of how to use it.