View Full Version : Working High Idle with GM PTO switch

10-05-2003, 07:21 AM
I figured out how to get the high idle to work using the factory GM pto switch. For those who don't know , GM pre-wired in a plug behing the dash area near the airbag disable switch(reg. & ex-cab)that the PTO switch can be pluged into. I will find out about crew cabs soon as my friend wants to hook this up in his truck also. Also this was done on a 2002, I assume 2001 are the same but cannot say for 2003.
All right, on to the fix to get it to work. GM did all the wiring for you (through the firewall etc.) except they terminated the wire that should go to ECM terminal C1-71 at a plug located in the underhood fuse center. Plug C106 for those of you with wiring diagrams. To access it you have to remove the WHOLE plastic fuse center cover (disconnect batteries first!), it snaps out of place after removing the semi-circular brace that runs from the firewall to the ds fender. After finding this plug(I will take pictures soon) all you have to do is get a female terminal to go into the plug and run about 6 inches of wire to the ECM as it's right there. You could also splice around the plug to avoid having to mess with getting a terminal.
I like this method better as this is the ONLY wire you have to run, no messing with trying to run throught the firewall or finding & fusing power. The switch is already fused through the cruise fuse in the fuse center, so power delivery is taken care of.

I cannot say for certain if it will work w/o reprogramming the ECM as this was the first thing I had done figuring that was the problem. I will be installing this for a friend soon so I can answer this better then.
I also don't have a good part number for the terminal that goes in to plug C106 as the dealer computer gave the wrong part# but I was able to make the terminal work after a little modification.
The best advice the mechanics at the dealer gave me when looking for terminals like that is to cut one out of a neighboring slot and bring it to them to match up. Makes things MUCH easier.

10-06-2003, 07:57 AM

I searched for CONNECTOR C106 (http://forum.thedieselpage.com/cgi-bin/ultimatebb.cgi?ubb=get_topic;f=3;t=004972) on a few occasions and thought that it could be found beneath the underhood fuse center. I lacked the initiative to remove the fuse center to verify...

"I was not successful in finding connector C106 on my truck. I poked around for a good 15 minutes or so...and had a strange feeling that I had tried this exercise before

There are few connectors UNDER or within the underhood junction block...I did not take it apart to look however...that location is a prime suspect at this point...

I vaguely think I remember...maybe...that there is a connector on the leading edge of the junction block when you take off the top, release the tabs on the engine side, and pull the entire plastic assembly upward"

Thanks for the solving the mystery. http://forum.thedieselpage.com/ubb/icons/icon14.gif http://forum.thedieselpage.com/ubb/icons/icon14.gif

10-06-2003, 03:32 PM
I've been working on this a while myself. Finally got all the terminals and had the time to rip apart the truck.
The service manual CD's give approximate locations of all electrical connectors. This helped immensely in finding this one. If you need help finding a connector in the future let myself or someone else with the cd's know and we can look it up for you. Saves a lot of head scratching since most of them look the same.

So far all good with the install, except it surges once and a while at the 950 rpm setting. I may have it reflashed for the variable rpm mode to eliminate this.

[ 10-06-2003, 03:43 PM: Message edited by: Spoolin'It ]

10-07-2003, 03:45 AM

So how does the PTO switch work? Do you still have to turn the cruise stick on and then hit the set button after you have truned the PTO switch on? Or can you just move the PTO knob over to the set position? I am currently using the PTO switch for my SPST switch for my high idle and am just curious if it could be self contained and not have to use the cruise stick at all.


10-07-2003, 04:26 PM

Reguardless of cruise switch setting turning the PTO switch to ON gets the first 950(?)rpm setting. Rotating to set turns on and off the second stage 1200 rpm. If you want to get to the third 1800 rpm setting you have to use the resume on the cruise stick. The cruise set button still gets the second stage also.
I have to go in and fix the weatherpack connector grommet on the C106 connector, hopefully this week-end. I will take pictures of its location then if you are interested in hooking up this way.

10-08-2003, 07:18 AM

So since I already have a wire into my C1-71 terminal into the ECM, all's I really have to do is find the C106 connector and connect the wire frrm the ECM to it?? And then plug the PTO switch into the provided connector behind the dash? Sure would help elimnate some wiring I have.

Sounds easy enough!

I'd love to see some pictures to help things go a little smoother when you get a chance.

Thanks! ;)

10-08-2003, 03:02 PM
Originally posted by 3-Fan:

So since I already have a wire into my C1-71 terminal into the ECM, all's I really have to do is find the C106 connector and connect the wire frrm the ECM to it?? And then plug the PTO switch into the provided connector behind the dash? Sure would help elimnate some wiring I have.
Thats it, the biggest pain will be getting a terminal to fit the C106 plug. You could cut & splice around it or as I said above cut off the terminal next to it and bring it to the dealer to match up.

Also I haven't verified that it will work without reflashing the ECM as this was the first thing I had done before realizing there was a wire missing. I don't see why it wouldn't work though.

I'll get a picture taken this week-end.

10-22-2003, 05:17 PM
What is the part# for the P.T.O switch, and the connectors that are needed to complete install

10-23-2003, 10:35 AM
PTO Accessory Kit Part # 12497678

Contains the PTO control switch, instruction sheet, and PTO interface wiring harness (includes a mating connector to the PTO interface connector and approx. 3 ft of blunt cut wires.)

Wiring provisions for in-cab PTO Control switch is provided in most of the Light Duty trucks with the L18 or LB7 engines only.

10-23-2003, 04:32 PM

10-30-2003, 06:11 PM
My 03 crew cab does not have the airbag disable switch. Any ideas on the dash piece to mount switch?

10-31-2003, 12:15 AM
You have a pocket there, right? You can buy the 4 place panel and put the factory switch in its factory location.

11-15-2003, 01:24 PM
Having trouble with locating whats needed to be done under the hood.Any body have pictures.

11-16-2003, 08:50 AM

Check out KENNEDY DIESEL'S TECH TIPS (http://www.kennedydiesel.com/techtips.html). There are pics of the TCM and ECM locations in the install instructions.

11-23-2003, 05:27 PM
Sorry this took so long but I finally got some time to take some pictures. Hopefully they load....


Here is a picture of the fuse box with the plastic cover removed, it just pops out of place after removing the fender/firewall bracket and releasing the latch that is against the fender well.


Connector C106 is shown here, it is the 6 terminal flat connector. All that is required from here is to run the wire from female terminal c of this connector to terminal c1-71 of the ECM which is 6" to the left of this picture. I can't remember if the terminals are marked but the light green wire is the one you are continuing from the male side.

Any questions, let me know.

[ 11-23-2003, 04:50 PM: Message edited by: Spoolin'It ]