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O/D Lock Switch Relocation

878 Views 13 Replies 4 Participants Last post by  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.


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