jumper

I always drive in Tow/Haul mode and wanted to have the truck default to T/H so I don't have to hit that button on every startup. So, I rigged up a timer to emulate the T/H button push about four seconds after startup.

I bought an IDEC GT3W-A11D12N interval timer off of ebay and the compatible SR6P-M08G screw terminal base from Amazon for about $40 in total (you need both). This timer has a number of operating modes governing how the unit's two separately controlled timer circuits behave relative to each other. Each timer controls its own set of normally open and normally closed circuits. This is quite the industrial quality timer.



You want to use Mode "H" in which Timer 2 (T2) fires once following Timer 1's (T1) timeout which begins when power is applied to the unit. Nothing else happens until the unit resets when power is removed (key off). T1 is set to about 4 seconds to allow the engine to start, then T2 is set to about a 1/10 second to emulate the T/H button push. So, upon key-on, T1 starts counting down, then upon its timeout, T2 fires and makes a connection between the two T/H control wires which enables tow/haul mode. No resistor is required, apparently.

To do all this, wire an ignition switched power source to terminal 7, and a ground to terminal 2. Then connect the T2 common (terminal 8) and the T2 normally open (terminal 6), one to each of the two wires coming from the T/H switch on the gear shifter using taps (e.g., Scotchlocks). These two wires are found at a white connector to the right right of the steering column with a green and a blue wire running downstream, and a pair of black twisted wires above the connector heading to the gear shift. I tie-wrapped the timer to the steering column housing. Note, T1's terminals are not used since its job is just to delay the button push emulation.





Now when I start the truck the T/H light comes on after about four seconds following a soft click as the T2 NO contacts close and open and make the T/H button push for me. I'll never have to hit the T/H button myself again, although it does still work!

torquefan

Cool project, thanks for sharing!

jumper

Now that tow-haul is set automatically on start-up, that frees up the T/H button for dedicated use for managing the BD overdrive lockout mdule instead of piggy-backing on the T/H function.

I cut the wires between the T/H button and the ECM, attached my T/H relay to the leads headed to the ECM, and wired the T/H button to the BD OD lockout using their instructions for wiring in a dedicated switch.

Tow-haul is now enabled on startup and OD lockout is enabled with the old T/H button. As a plus, cycling OD lockout in and out used to also cycle the T/H off and on as well, no more.

I'm happier than a pig in S*it. My 2005 truck now only operates in Tow-Haul, and I can separately and independently control OD lockout with what was the T/H button that's now the OD lockout button.

OK, the OD defeat function doesn't work if OD is already engaged. Weird, but manageable. Just never try to lock out overdrive when you're IN overdrive. I can live with that.

Anyone want a wiring diagram, let me know; I'll create one.