Electrical harness

General

The orignal Thunderbird, can run with one electrical wire , if You look away for the spark plug wires. I'm talking about the power to the coil. The advantages with the modern cars are better throttle response, less polution, and many other enhancements over the good old cars. These advantages comes as a price, being the coplexity of the computer and all the sensors and actuators. The 97 MarkVIII computer has 104 pins, where few can be ignored. When I bought the donor motor, I also bought the Computer, the computer harness, the engine room harness, the engine harness, and the main harness from under the dash. these harness'es , at least the one for engine compartment and under the dash, includes a lot more than what I would need, but it is a proper starting point.

When the harness is connected in the donor car, You can easily see what the dozens of connectors actually connects to, but when You get it all in one big box, things get easily more complex. The very first thing I figured out ( and You do not have to be a rocket science engineer to figure that out) is that I needed a wiring diagram for the Mark. E.Bay is a great source, and it did not take long before the "Electrical and vacuum troubleshooting manual" were on its way. This book has all wiring diagrams for the entire car. First step was to identify all the connectors, and mark them accordingly, and cut away the connectors that were not of interest, not only the connector, but the entire wires, so each harness had to be opened and temporary hold in place with some strips or similar.

While working with this, and looking on the wiring diagrams , it become clear that the wiring book had a severe shortcoming compared to my needs. All the wires in the book has a "loop" number, and as I come to open ends that I would have to connect somewhere, I added cable marks using those numbers. The shortcoming of the book is that there is no way possible to find on what page example loop "16" is described. I had to pay my son to go through the relevant pages, and punch in all the loops, grounds, connectors and splices refered to on each page, into an Excel spreadsheet. Later I could use that data to search any connector or any loop to find where the wiring diagram was. I still have it , if You need it.

Here the spreadsheet shows all the pages loop ( wire ) 16 is documented. 

During the process of removing loops for the light switch, side marker lights, heated seats etc, the harnesses became thinner and thinner, while I ended up with an impressive "hill" of wires that I could dismiss. However, it is not correct saying that these harnesses now are thin / slim, it is just that they are extreme heavy in the original Mark VIII

Atually 3 "hills" of wires and connectors, that were removed from the Main and engine bay harnesses

I also ended up with quite some wires that had to be spliced into the original Thunderbird harness, into a new instrument panel power distributon, and guess if all connectors were where I needed them on the harness?

I have made brackets for all connectors, but it was hard to reuse the connector fastners, so I had to order these from Ford, but initially they said it is not listed as spare part, but if You do not give up and keep asking and pushing, one day the Phoenix dealer I wisited could proudly tell me he had found them. And here is the part number: F1TZ-14A163-E

This what this clip looks like, and  later I also found these clips at Au-We-Co with part number 20569. On the "red" picture You can also see the contact to the left hanging loose, but the bracket are ready.

Computer harness

The placement of the computer had to be such that I would avoid extending the wires due to the quantities of wires. However , I had to open the harness and change around on the branches a bit, but it is basically stock. I only re-routed one wire in the harness to avoid running the speed sensor signal all the way around the engine bay and back in under the dash. The engine harness would also have to reach the computer harness, as it is to many wires to extend. See the computer page for a picture of the location of the computer.

I considered to use a 96 computer, as it did not use a theft system , like 97 and later. The reason for attemting to use a 96 computer is that I though I would be able to use it without re-programming. It is also such that there are only 4 coil outputs on the 96, firing these both with piston on top and on bottom, but the 97 has 8 coils and need 8 coil outputs. I think it caould be wired such that each of the 96 coil drivers would feed 2 of the 97 coils, but not 100% sure. The problem ended up being that I did not want to use the emission system so it would fail the testing from the computer and the hidden check engine light would always be on. Due to this I would have to have the computer re-programmed anyway, so then it is better to use the 97 computer. If You use the 96 computer with the 97 harness, then there are additional inputs that have to be re-wired also. My spreadsheet shows them all.

Engine harness

The engine harness were almost unchanged until I figured out that I would have to use the 1996 intake. I like the look of the 96 intake, as it leaves the big nice valve covers exposed, and provides better hood clerance. The throttle plates under the intake on both sides are vacuum operated on the 96, while it is electrically operated on the 97. However, it can easily be re-wired, as the signals to and from the computer are the same.  I routed the right side wires that not are for fuel injectors under the intake to make a cleaner engine. The solenoids for the EGR and the IMRC is screwed to the firewall as the EGR sensor. These 3 units were part of the connectors that belong to the engine harness, and they still are, but I made a specific branch for these, where this branch starts at the big firewall conector beside the heater. This will prevent that wires will break off due to engine movment. Now there will be no movement. On the Mark the EGR and another solenoids is palced on the valve cover, and that is why I moved it away out of sight. The EGR sensor is placed on the firewall just because the EGR pipe have now taken the place behind the Left cylinder head due to the intake swap. Due to the intake swap the air inlet temp, throttle position sensor and a few others had to be relocated, and wires in some cases extended. Wires being to long were routed in a "S" shape in most cases.

If You look carefully, You can see the takeout for the solenoids close to the main connector, that connects to the computer harness. The picture also shows the struggle to make the Engine harness long enough to meet the Computer harness connector, as well as what it takes of mods to the engine harness that electrically spoken, is unchanged.

This picture shows where the Engine harness leaves the engine. I have made a support bracket for the harness, as well as some protection for the branch to the left hand coils. There is also a bracket to hold the transmission dipstick.Without the protection mentioned above, the dip stick interfered with the harness. Kind of unusual to have the transmission dip- stick on this side of the engine, but that was the only place I could find. In this picture You might also notice the silver colored throttle cable and cruise control cable bracket

Engine bay harness

The engine bay harness did have a lot more wires than I needed. First , I identified all the connectors, and marked those that I did not want to use like connectors for lights, side markers,  ABS etc. Then these connectors and their wires were removed. I did however keep some 4 inches at the firewall connector, just in case I cut a wrong wire, or if  I later would need some additional wires through that connector. I decided to re-use the engine room fuse box / power distribution box, and it is placed on the inner fender almost at the front on drivers side. I saved it because of convinience, and I can not agree with myself if I like it or not. The good thing about keeping it is that there is more than other things to modify, and this can actually work. The wiring diagrams will also have less mods, something I feel is important when I later will have to trouble shoot anything electrical. It is of great importance that You update the wiring diagram in the Mark manual, else You will be lost at some stage.

Main harness

 The under dash harness that I like to call the main harness is the harness where most wires have been removed. Due to where I posisioned the various items, I did not have to splice in additional lenghts all over, just here and there. The Instrument Fuse panel were dismissed as it had to many fuses, and it  just did not look right to be re-used. Some 8 of the wires on the fuse panel had to be attached to the new I/P panel so these 8 wires were identified, and cut close to the fuse panel and marked with the loop number, while the majority of the wires that would have to be deleted, were followed all the way out and removed one by one. Same method were used on all connectors.

Left Picture shows the connector that connects the main/ dash harness with the engine bay harness. It will be more or less hidden under the steering column. The connector had to be lowered like shown in the picture above, relative to the floor, else the brake pedal travel would be affected.

The right picture shows the bracket for the computer and the computer connector, and the ongoing mess around the now unwrapped main harness. After starting the engine, and it all works, the harness will be protected with harness tape ( no regualr tape) and protective harness hose whereever there is a chance for mechanical tear and wear, and the dash will be installed. ( it is now easy access )

The main harness also has a branch that runs backwards to the Fuelpump module and the fuel safety cutoff switch. As I have dismissed the emission system, I'm not using the fuel tank transduser signal.

When You buy such a Main harness, they might cut it such that You do not have the complete branch running backwards. Make sure You get the connectors with a pig tail for the fuel pump module and the safety switch, if You are planning to use the mark Fuel pump.

Transmission harness

The transmission harness is electrically spoken unchanged, but it is re-routed such that the 2 connectors against the main dash harness , is now pointing forward. This was done because the transmission tunnel was narrower at the  rear, and the shifter were also in that area. An bracket were fabricated to support the 2 big connectors. 

The original T.Bird harness mods

The original Thunderbird harness that runs under the dash and out through the firewall and back to the tail lights also needed some modifications as some functions have to be provided by the Mark harness, and others would make sense to modify. I removed the wires related to the original generator and charging relay, including the wire to the charge lamp, as that now comes through the engine harness. The starter wires ,ign wire for the coil, and horn wire had to go, and I do have the brake switch on the pedal assembly, so it is no longer going through the firewall. The backup lamps signal now comes out of the mark harness, and are spliced into the Thunderbird harness at the shifter. This is not a complete list, but it gives You an idea. You might look at the steering column for details on the horn wire.