I was hunting around for a way to determine when my T/C goes from locked to unlocked when towing (other than watching for the slight tach increase), and knew there had to be a signal to the T/C lockup solenoid. Well, I found THIS POST at TheDieselStop.com detailing (I mean really detailing) the addition of an LED. I found the wire in question at connector C172 on the passenger side of the firewall. (Its' a grey connector under under a snap-off plastic cover/metal bracket assy.)

The discussion also gets into adding a T/C lock-up switch, which I think could come in handy as well, but I'm hesitant to install this. I assume Ford knew what they were doing when they programmed the PCM to lock/unlock it under certain conditions (and I don't see any long-term reports on the effects of the manual override switch in the linked post). It would be nice, though, if the trans would downshift directly from OD to 3rd without the "3.5th-gear" slip mode. It might also be nice to get a little dynamic braking?

I'll be adding the LED, but would like to know others' thoughts on the switch.

Andy

 

The reason the 4R7x transmissions take a moment to downshift from 4th is because the transmission needs to fully release the overdrive band before the forward clutch comes back on. If that doesn't happen then the transmission becomes mechanically locked. Kind of like park and is bad.

I have 0 opinion on a light or switch though, I only wanted to address that one concern that you voiced to try and explain why it has to be that way.

Darrin

 

Wow, that's some deal there...

While I can appreciate the function of this mod, and in a diesel, it probably makes sense, since the rpm range on one is very small compared to a gas engine.

In my case, I've become so accustomed to the shift patterns of my truck, that I can tell what's going on pretty much by feel now... Then, it only takes a second to blip the gas to check the tach since I'm already looking there anyway!

My vote is to leave the wiring harness alone and I don't even like the idea of a tuner, so that'll tell you where my 'conservative' mind is!!

But more power to those that have the gumption to do this kind of stuff!

Mitch

 

Well, it sounds like having an override switch activated would be a bad (possibly very bad) thing if the trans wanted to downshift out of OD, then. Trouble is, though, it's not just an OD --> unlocked --> 3rd shift. It seems like it likes to stay in the unlocked condition too long (or at least longer than I'd like it to). As soon as I see the tach jump, I hit the OD button, and knock it into third. Maybe I'm exhibiting some "conservative-ism," too.

Regardless, that pretty much seals the deal against the switch for me. The light OTOH, couldn't hurt anything.

Thanks.

Andy

 

Noting wrong with conservative, so long as it doesn't slide over to paranoid fear.

Unfortunately, I don't tow enough with mine to get the "feel" for it, so the light will be a better indicator for me.

Andy

 

Mitch

 

Thought I'd bump this up for two reasons:

1) I did end up putting in an "override/lockup" switch in, and used the "off" side of the cruise control. Locking the T/C did work, but also set a CEL when the trans wanted to unlock but couldn't. I ended up using it spartingly, then eventually not at all.

2) I'm planning to hook up the locked light in my new-to-me '03, and don't want to hunt through 4 pages of subscribed threads to find it again.

Andy

 

Well, I took some pictures when I swapped this over to the new truck, and thought I'd post them in case anyone finds this thread and needs the references.

Below are a couple of pics of the wire used to drive the TC lockup indicator. The connector is C172 which is located to the rear (nearest the firewall) under the start solenoid. The wire is purple with a yellow stripe, and goes to ground when the TC is locked.


You can see the T connector here.


And a close-up.

I hope this is helpful to someone.

Andy