Post # 8 Rear wire harness
I have always been intimidated by the thought of building a wire harness from scratch. I tried to get the harness from the truck the engine came in but the recking yard used it to upgrade their test rack. That forced me into building the wire harness.
I purchased an installation manual for the engine and the Autoshift transmission. When I opened the manuals I became even more intimidated, but I kept on reading. I decided to take it one pin at a time and find out what that pin did. As time went on I began to realize it was not as compicated as I first thought. I learned the ECM does all the work; all I had to do is hook it to the proper light, sensor,switch, computer, etc. ( nothing to it
)
The vehicle plug on the ECM has 68 pins. Each pin was studied and I figured out what it did, if it was needed, and what it was hooked to on the other end. The manuals are pretty good at helping figure this out if you are patient and can search the manual for what you need.
The next step was to draw a schematic that I could follow when building the harness.
The parts to build the harness are a little difficult to find. You can always get them from Detroit but we all know how proud they are of their parts. The engine ECM uses Tyco pins,connectors, and shrouds. The Manual has all the numbers listed of both Tyco and Detroit. I was lucky because a friend of mine got the Tyco parts as a sample and he buys from them all the time. I also used him to purchase the proper wire and the twisted shielded pair for the J 1939 communications. The transimmision connectors and pins ( both the 18 pin and the 30 pin ) can be purchased from Wytek. For all my bulkhead fittings I used Deutsch connectors purchased from Ladd Industries.
All of the pins are crimp type. It is important to use good crimping tools to accomplish this task. With a little practice and good tools a very good connection can be had.
I first designed a rear electric panel for the coach. By using relays for the trailer ( toad ) plug, the strater, and the dash air functions I only had to use lower amp wire for the runs to the front of the bus to control these functions. The panel also has a master shutoff for the coach, fuses for the DDEC and the transmission power and fuses for the runs of power to the front of the bus.
The Autoshift and the engine have to talk to one another. This is accomplished by using J 1939 communications. I chose to use gold plated pins and sockets on these wires. The price of these pins is not a lot more and it is important to get a good connection on these wires. Also J 1587 is used to relay information between the engine and the transmission and the front of the bus.
To keep track of the wires I am using a number system. I used clear heat shrink tube to hold the number in place.
With the rear panel complete I then ran the wires that tied the rear panel to the ECM's, the engine ECM to the transmission ECM, the ECM's to the front of the bus and the rear panel to the trailer plug. Each wire was checked for continuity, numbers checked on both ends, and numbers recorded along with the corresponding pin or socket at the Deutsch connector, or ECM pin. When running wire add a couple extra wires in the harness; you will be glad down the road when something was forgotten.
I do not have the finnal schematic finshed and it is only the rear part of the harness. When I am finished with the schematic I will be glad to pass it on, but remember it has not been tested and it will be a year or better before it will be tested.
Pins and Sockets
Deutsch connectors
Engine ECM
Numbering system
Rear wire harness
Rear panel
Rear panel schematic