[SFGiants]

For the auto guys out there, has anyone relocated their O/D switch? I'd like to install a fuel pressure gauge in the dash where it sits. I already have a block of accessory rocker switchers with a couple blanks remaining, so was thinking I could simply add a switch and connect it there.

Anyone know how complicated the stock wiring of this switch is and if this would be possible?

I'm also open to ideas for other locations for the FP gauge. I already have the 3-gauge A-pillar, and am not too big on the steering column pod that appears to badly obstruct the speedo.

 

[9297oldram]

I don't know why you couldn't relocate it to a rocker switch, when you unplug the wires from the back of the dash switch just add longer wires to the existing ones that will reach to the new switch. In the 11 years that I drove my 97 never once did I ever shut the OD off so unless it's something that you always do it wouldn't matter where you would relocate your switch.

 

[dauntless89]

It will work as long as it's momentary and the same topology (NO or NC) as the stock one. This is just a "trigger signal" to the PCM to switch OD/TCC behavior.

 

[9297oldram]

You could remount the OD button when you remove it so that you don't have to buy a momentary switch.

 

[dauntless89]

It needs to stay a momentary switch if he wants to keep the PCM in control of OD/TCC.

 

[SFGiants]

I don't know why you couldn't relocate it to a rocker switch, when you unplug the wires from the back of the dash switch just add longer wires to the existing ones that will reach to the new switch. In the 11 years that I drove my 97 never once did I ever shut the OD off so unless it's something that you always do it wouldn't matter where you would relocate your switch.

Thanks. I couldn't see why not either but wanted to make sure.

Daily driving I don't use mine either, but for the occasional tow I find it useful when pulling grades. The factory location, as well as my relocation, are absurd places to place such a switch but I don't use it enough to care.

 

[SFGiants]

It needs to stay a momentary switch if he wants to keep the PCM in control of OD/TCC.

This is exactly the sort of technical info I was looking for. Going to research this some more. Thanks Dauntless.

 

[9297oldram]

You can buy some really small momentary switches, if you decide not to use your factory one and remount it.

 

[SFGiants]

So in laymen's terms, a "momentary" switch is a switch that returns to its original position when pressed (as the factory O/D Off button does).

I'm guessing this is important because if it was a conventional switch and was toggled on, the switch would override the PCM and TC would remain locked even at slower speeds when the truck goes into 1st & 2nd?

Looks like this is what I need. https://www.amazon.com/Genssi-Rocker-Switch-Momentary-Type/dp/B00DOHT0V6

 

[dauntless89]

In this example, let's pretend it's a normally-open switch. I don't recall if the real-life switch is normally-open (NO) or normally-closed (NC). It's probably NO but check your FSM.

Being momentary and normally-open, the contacts are not touching and only touch when the button is pressed. The contacts return to not touching as soon as the button is released. If I remember correctly (it's been like 5 years since I had to troubleshoot this switch), one side of the switch goes to ground and the other goes to a terminal on the PCM. When the button is pressed (contacts close), the voltage on the PCM wire goes from 5v(?) to 0. The PCM detects this change and switches the trans control to "OD Off" mode. I believe the little indicator light in the switch actually gets its power from the PCM as well, indicating the switch to (or from) OD Off mode. This mode is active until another "blip" to 0v on the signal wire. Then the PCM switches back to normal mode and stops supplying current to the indicator light.

A conventional toggle switch, when used in this manner, will at-best require being toggled twice to get the intended result of activating or canceling OD Off mode. Worst case, it may confuse the PCM, getting it stuck in a Kirkensian "does not compute" logical paradox loop until the power is cycled.

 

[dauntless89]

Also, the valve body (in stock form) does not hydraulically allow locked downshifting, or TCC lockup in 1st and 2nd. All of this can be accomplished with valve body mods and manual override switches, but the PCM is programmed in accordance with that, so it will never command TCC lockup in 1st, 2nd, or when downshifting.

 

[SFGiants]

All very helpful stuff, Dauntless. Thank a lot.

I think the easiest and most fail-safe approach will be to simply relocate the factory button. I'll try cutting a square in one of the plastic blanks on the rocker switch block. With any luck, the factory wiring harness is long enough and I won't even need to worry about lengthening it as it's only moving 3-4 inches towards the passenger.

 

[alanack6795]

Swap in a 98+ column shifter. Best way to go for a clean install.

 

[SFGiants]

Swap in a 98+ column shifter. Best way to go for a clean install.

This would certainly be the cleanest. Are you aware of any write-ups? I haven't been able to find anything. Seems it isn't a terribly common mod.