C4 to AOD Neutral Safety & Backup Light Switch Splicing

A fellow enthusiast has a 1973 Mustang grande in Poland. When he acquired the vehicle it was in the USA (Massachussets). So, he needed to have the Mustang shipped to his country. When it arrived he found the original 302 and c4 auto transmission had been replaced with a 1985 5.0 liter (302) engine with an Automatic OverDrive (AOD) transmission. When I first of that powertrain having been installed I quite literally shuddered, as the new owner is likely not aware of the large differences between the 1973 and 1985 technologies (electromechanical ignition vs computer controlled) when it comes to the difference in powertrains. I have decided to go retro with an electromechanical fuel and ignition system. Why? Two reasons, it is easier to use the 73 based technology, as opposed to trying to introduce an EEC II system into the 73 Mustang. Much less trying to install an aftermarket EFI system with an aftermarket electronic ignition system. Also, the Fuel Injection system for the 1985 5 carburetor.2 liter engine has already been replaced by a 4v carburetor. Those were all reasons enough for me to try to go old school in this project. Although I may end up suggesting using a Pertronix aftermarket ignition system. The distributor needs to be replaced with something other than the one once used wswith the EEC II system, just for the benefit of era specific familiarity and technology if nothing else.

There are several things not working well at this time. The ones that got my attention first was the engine will start when primed, but will not continue running., and it wont crank using the ignition key. So, what to take on first.... Well, I felt one immediate area to consider working on was to see if anyone had bothered to convert the C4 Neutral Safety and Backup Light Switch (NSS/BUL) wiring over to the AOD's NSS/BUL style harness. I asked a few questions and got a reply, and some photos, that answered that question. There is nothing connected to the AOD NSS/BUL that is installed in the AOD. And the AOD's NSS/BUL unit has seen a lot of road grime or corrosion. I also asked about the fuel lines, and found the owner had thought (either because he was told, or he presumed) that "the fuel pump in the fuel tank" needed to be replaced. (Okay, folks, stop rolling your eyes). Yes, I know, there is no elecrric fuel pump in the 1973 fuel tank. Further, there is no mechanical fuel pump on the 985 5.2 liter engine either.

As I understand it, no mechanic in Poland is interested in working on this Mustang. So, I decided that I would take the time to help the best I could from half way around the planet. I put together several shop manual and schematic snippets to help with the first two parts of this project. I asked the owner to remove the fuel tank sending unit to inspect the fuel sock filter, and to test the sending unit for correct operation (the fuel gauge was not working). An ulterior motive was to show that indeed there is no electric fuel pump in those stock tanks.

So, as it turns out the first of the two items I wanted to help was to be me splicing a C4 NSS/BUL unit's wiring harness into a Ron Francis AOD /NSS'BUL pigtail. I had done this for our 1973 Mach 1 about 3 years ago, and it worked out very nicely. The second thing I wanted to do was get a quiet electric fuel pump, a fuel pressure regulator, and an electric fuel pump shut-off switch, then assemble the various devices enough to help prepare it for installation into the Mustang. An aside, the 1985 5.2 liter engine has a plate covering where the mechanical fuel pump would have otherwise been located, as its oem fuel pump is an electric unit. I did not feel comfortable trying to shoehorn the 1985 electric fuel pump into a 1973 fuel tank, although my instinct is to believe it could have been done. Hence the aftermarket configuration for the fuel pump and related components..

Anyway, those are my first two contributions to the 73 Mustang Grande project. And this video shows how I spliced the C4 NSS/BUL harness into an AOD NSS/BUL pigtail. I also show what (little) I did with the NSSBUL unit to help prepare it for its installation.

I am pretty certain the status of the Mustang I shared in this description is accurate. There is a definite language barrier, as Mr Z does not speak English, and I do not speak Polish. He has an interpreter helping him, and I found that Google's gmail has a translation feature that actually works pretty well. I am not quite trembling with fear re: the next few steps after I get these first two items handled.

For anyone interested in seeing my prior video I did showing how I spliced a C4 NSS/BUL harness into an AOD pigtail for our 73 Mach 1, that video is at the following address:

C4 neutral safety switch    • 1973 Mustang AOD Neutral Backup Switc...