The `93 D-250 had the dash and wiring configured for the Cummins.

The `92 (`82) D-350 Dually had wiring from what I assume is a `92 Cummins truck, but changed over on the engine side to connect to the 440 (or any other gas motor).  The Dually had the wiper motor and connections for power doors just like the `93, so I assume that they swapped dash and cab/firewall harness over from the `92 Diesel truck back when the VINs were exchanged.

Regardless, the most reliable thing would be just to use the `93 Harness for everything.  Here were the major differences between the equipment on the `93 and the harness found in the Dually:

–`93 has ABS module
–`93 has Cruise Control (harness and Steering column)
–`93 was wired for a “Cargo Lamp” on the outside of the cab (makes hitching up the 5th wheel easy at night)… Dually doesn’t have such a light
–`93 had power mirrors (Dually has manual towing mirrors bolted to the door).

Photos were taken to document the entire dash removal process from both trucks.  The photos serve as an archive for anything I might not recall during the process, and are highly recommended for anyone doing a major swap like this (engine, wiring or similar).

GETTING THE DASH OUT
The dash in the `80-`93 trucks (and likely prior years) is screwed to the cowl underneath the windshield on the interior side.  Excess rubber is designed into the windshield gasket to cover the screws holding the dash lip to the truck.   Having taken apart three trucks now (`82, `86, `93) I have not seen glue over the dash lip, it should be easy to remove.

Example of cut-away rubber from the windshield gasket, to enable removal of the dash.

To get the dash out, use a long blade utility knife to slice away the excess rubber below the windshield.  Use care not to cut away rubber that actually holds the windshield to the cab.  Basically, you will want to cut at an angle about halfway between the windshield and the dash.

Rubber windshield gasket cut-away from dash lip, near defrost vent.

WIRING HARNESS MIGRATION EFFORTS
Turns out the wiring certainly had been swapped from a newer truck into the Dually at some point in history.  There were 14 wires between the main dash harness and the port hole out to the Driver’s door (it must require 14 wires to operate Power Windows, Power Locks, power mirrors and the 6×9 Speaker).  Luckily all of these 14 wires matched from truck to truck.  So, they all needed to be cut, soldered and stripped.

Note: I actually took the extra time to take the Dually door apart to investigate if it would be easier to pull the entire door harness out.  Turns out it was not possible to pull all of the wires out of the door easily, soldering would be faster.  I also went online to my local library web site to try and compare wiring diagrams from truck to truck.  Unfortunately the wiring diagrams in the online repair manuals were not clear and difficult to decipher the color code.

Bare wires with Shrink Tubing pre-installed, and solder splices crimped on a couple of the wires.

To solder the wires, I needed a compact, but quality method for making the connections.  Solderless crimps on each wire would end up too large once the harness was wrapped back up.

A few wires soldered and with shrink tubing installed over the splice.

So, I cut the plastic off the solderless crimps and used just the metal sleeves to crimp and then solder each wires.  To cut the plastic off, I used a utility knife and made sure to cut safely and away from myself.  It required a single slit all the way down each connector to get the metal sleeves out.  Some plastic pieces required peeling from around the sleeves to get them off.  Other sleeves were able to slide out by hand.

More splices installed and soldered.

CRIMPING AND SOLDERING THE WIRES

1.) First, the wires were color-coordinated and lined up from harness to harness.
2.) A shrink tube was placed on one side of the wires to be soldered.
3.) Then, the metal sleeve was placed and crimped over each set of matching wires.
4.) Next, each metal sleeve was heated with the solder gun and solder was melted into each end of the sleeve.  The solder improved both mechanical and electrical connection between the wires.
5.) A pull test was conducted after the mechanical crimp, and again after soldering had cured to verify a good connection.
6.)  Last, the shrink tubing was slid over the soldered joint and shrunk using a heat gun.  This provides insluation for each of the wires.
7.)  After that, the entire harness was taped up using standard UL listed black electrical tape.

All wires spliced, soldered and with shrink tubing applied.

In the photos, you can see that the finished, spliced harness is not much bigger in diameter than it originally was in the section of the splices.  A big, solderless crimped assembly, without solder, would have 28 points of potential failure of the crimp and would be about twice the diameter of the original harness.  There simply isn’t enough room behind the dash for that, nor will there be much time to troubleshoot wiring later – I wanna get this truck on the road quickly and reliably!

Wires taped up with black electrical tape.

For the remaining harness installation, the original routing of the wires and clamp points was selected.  This meant routing some of the wires behind the defroster vent assembly and around the HVAC unit.

SOME NOTES ABOUT THE HVAC UNIT
The HVAC unit on the `82 Crew Cab had it’s motor resistor built into the HVAC unit.  If any leaves or flammable debris got into the HVAC chamber, the resistor could catch the debris on fire.  This also happened in early 1980′s Fords, which had the resistor down low in the box, where leaves would collect and get sucked into the system.  On  the `93 D-250, this resistor was placed up in the cowl, away from any area where flammable debris was likely to collect.

These HVAC units involve a number of small vacuum tubes and one mechanical control cable going from the main airbox to the dash control switch module.  To disconnect, simply:

1.) Disconnect all electrical connections from the back of the switch module
2.) Carefully disconnect the mechanical control cable from the HVAC box (you have to find a way to depress the red tab below the cable, on the clip)
3.) Carefully (but firmly) disconnect the vacuum lines from the back of the switch module plug.  The colored lines and transparent connector will remain connected to the HVAC unit.

As if it wasn’t clear from the above post, I will be using the dash out of the `93 D-250, due to it’s superior condition compared to the dash from the crew cab.  This decision is due mostly to the condition of the plastic mounting tabs for the HVAC controls and radio.