Took me a while to get this right, and i ran without one for a while, bottom line, Roll racing sucks without towhaul!
If you have access to tuning software like HP tuners or EFI live you can do it yourself (given you are tuned by yourself, if not take your truck in to your tuner)
The process is simple.. Here are some pictures of what all is exactly involved.
With HP tuners...
With your VCM editor running and no other windows open, click on "Trans" up at the top
The Transmission window opens, and you're going to click over to the next tab called "Auto Shift Properties"
When you're there, you will see a total of three tabs, General,Shift time,and Shift pressure, Stay in General, and click on the drop down list next to "perf option" (known as tow haul to the truck guys) and select "One switch" save and export your file to your PCM.
then we have the physical side of the PCM to deal with and the Wiring, you're going to need a couple of things...
1. Momentary ground switch (i bought mine from Radio shack, make sure it's a normally OPEN switch, otherwise it will be grounded all the time and not work OR keep you in tow haul all the time)
2. This is a grounded switch, so i used some black wire the 2nd time around i wired my switch, use common sense and select a good gauge wire for the switch
3. Unused PCM pin with some wire left on it that is able to be spliced.. i used a terminal connector with mine for easy hookup.
here's the procedure
1. Cut power to the battery, you DON'T want to difibulate your PCM and fry it.
2. Use the appropriate socket and remove the bolts on the middle of both connectors. (or the just the blue connector since that's what we will be working with)
3.once your Blue connector is out, pull off the gray clip in the back to expose all the wires (be gentle, the clips can break easy). Notice there are ports/holes that the wires go into are all numbers, I want you to find #71 and poke through the yellow rubber.
4. take your PCM pin and push it though the hole and make sure it "snaps" into the blue lock on the Connector side.
5. Assemble everything back the way it was and wire your switch, mount it anywhere you want but make sure you GROUND it to a good source, Hook up one side of the switch to the Pin wire we installed on pin 71
6. Test it, if it's not working, go through everything again and make sure you went though all the steps correctly.
7. The way this is setup is just a basic momentary push button switch, there is NO INDICATOR as of now available because the newer trucks use class 2 data to "talk" with the BCM (body control module) and it knows to turn on the famous "tow haul light".
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Originally Posted by Botlfed
