First thing is first. I DO NOT take credit for the information below. My success at addressing the topic was directly related to the information provided to me by the people named in the following text and an enigine wiring diagram in a Chilton's manual. IF ANYONE for ANY REASON feels that any of the information below infringes on the rights or property of a business or individual then speak up and that portion of the post will be deleted immediately.

In addition, this is what I have found to be true in my experience and it may not provide the same results in your application. I take no responsibility for what occurs(good or bad) if you decide to apply this information to anything other than reading.

Now for the context. When swapping from an automatic trans to a manual you have the option of using either a manual PCM, your original automatic PCM(with some reported issues although non that I experienced), OR your automatic PCM and have it reflashed to manual programming or under a chip programmed for manual settings.

If you go with a manual PCM then let us know how it goes as I have no idea. I tried one that had no cruise function for about ten minutes. The truck ran fine but low and behold, I had no cruise, and that was not going to work.

If you use the automatic PCM as is and PREVIOUSLY HAD cruise control then it should still function as before. But remember, before you had no clutch and subsequently it WILL NOT disengage with the clutch in now. Some have also reported a wild lope idle at startup in this case.

If you decide to use the automatic PCM, that already had cruise control, and have it reflashed to manual programming or put a chip on it with manual programming your cruise control will cease to function. If you'd like it back then keep reading. If you decide not to have the PCM itself flashed to manual settings and use the chip only for that purpose then realize that when the chip is removed your PCM will revert back to its original automatic status. If this is the case and you take the following steps to make the cruise work then I have no idea what will happen when the PCM functions in the auto setting.

Jody Tipton of DP Tuner provided me with this prior to getting my PCM reflashed because I did not want to do it if I couldn't figure out how to keep my cruise:
"There is a communication line between the pcm and clutch position switch which even if hooked up goes to a different pin on the manual pcm.
Pin 29 for the auto harness has a tan and white wire which hooks to the OD cancel switch. On the manual pcm, that same wire is for the clutch
position switch. If you take the Tan/WH wire from the cancel switch and connect it to the tan/LB wire from the clutch position switch,
effectively you give the pcm back the signal to cancel/engage the speed control."


Info that Ryan of Bean's Diesel Performance posted on another forum. It was given to me by Jim(DZL JIM). This is concerning cruise control after a 12 valve swap:
--"Pin 31 should be hot all the time, thats the brake pressure switch black and yellow.

Pin 92 should be hot when on the brake and not otherwise, that brake on/off switch and is lt green.

Pin 29 looks like it needs to be hot all the time as well. Thats the clutch pedal position switch input/nuetral safety. On an Auto the wire should be tan and on a manual looks like tan and lt blue but both go to the same pin.

if all those voltages check out it should work as long as you have a speed input."

-- "It was wire 29...I added voltage and everything works including the safety switches....it is so nice to have cruise!!!"


Using their info and studying engine wiring diagrams for a while that were labelled 1994-1996 7.3L vin F I decided to do the following:
I spliced Pin 29, the Tan/WH wire, into Pin 31 which is Black/Yellow. Pin 31 is the brake pressure switch and my diagram shows it to be hot always EXCEPT when the brake is applied. After doing this I took it for a test drive and everything works as it should, all the cruise controls and brake disengage. It seems like Ryan is saying that you just have to verify 12v to Pins 29, 31, and 92 and as long as those check out it will work.


I've not tried it with my clutch starter switch plugged in but I THINK that since the clutch pin(formerly OD cancel pin) is wired to Pin 31 the cruise should cancel when the clutch is pressed after installation of a working clutch-starter switch. BUT I'm not positive. Especially since Ryan's info says Pin 31 is hot all the time and 92 is dependant on the brake.

Remember, this is what I did in my very specific application. I chose to commit to the auto PCM with manual programming in hopes of preventing future issues of having to remove chips, etc. I would imagine that the above information can be adapted to your individual situation successfully but check, check, and recheck before doing anything too permanent.

 

Very interesting.

 

Subscribed for later reading.