I have read the "Fast Idle Setup" on the Kennedy web site, but have a question about the switching to engage the fast idle.

Is the switch supposed to be attached to a hot 12V connection TO send power to B7 and/or B8 on the PCM when switched on

OR

does the power flow FROM B7 and/or B8 through the switch to a ground when switched on?

I think it is important to know which way the circuit should go.

Any help in the way of advice, pics or a wiring diagram would be appreciated.

I have a '99 GM6.5TD Burb.
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run switch lead(s) to chasis ground not 12v

Ok I still have some questions as the PCM on my 1999 6.5TD Burb does not seem to match the fast idle instructions on the Kennedy tech tip website.

I have attached 4 pics of my setup.

First pic = my PCM with the middle pig tail removed. The 3 pigtails are labelled PED2 (left), PED3 (middle) and PED9 (right). There are no markings for row "A" or "B" on any pigtail.

Second pic = my middle pigtail removed from the PCM slot showing the top with the blue removable lock which holds the wires in place. This blue lock has each wire slot numbered.

Third pic = The "pin in" openings with the top of the pigtail up. The only openings not used are holes # 7 and 8 in the TOP row. All others have existing wires. The Kennedy tech tips say that the "B" or bottom row should have # 7 & 8 open.

Fourth pic = The male pins in the PCM within the slot showing the pigtail can only be placed in the opening one way. Top up with the the currently empty #7 & 8.

QUESTIONS:
The Kennedy tech tips talks about 1996 and up PCM's, but mine seems to be different from the one described - other than the fact that # 7&8 are currently wireless openings.

Before I try throwing the switch and potentially frying my PCM;

1) If the high idle will engage with a voltage drop at pin #7 and/or 8 in the middle top row, how much voltage should I see with my voltmeter on these pins? 12volts would definately cause a short but should it be <5volt or <1volt at the pin?

2) Did GM change the PCM style at some point after 1996 - in this case there are several other wireless openings in PED2 and PED9 which could control the idle RPM?

My thanks to anyone/everyone who has some experience with PCM functions after 1996 or with a 1999 PCM.

im not familiar if they changed the pcm for 99. on my 97 you could tell whether it was row A or B by looking at the blue and gray pieces. they say on there what row and number. i cant help you with the voltage.

Hey take a look at those 2 wires zip tied with red tie to black harness in the 1st photo, I have 2 similar color when tips are touched to that metal dash support bar you have PCM draped over or any other GND I get hi idle & higher idle I don't remember the speed but it scared the mess out of me when it revved up when I closed the glove box back up.

I don't use them myself found it by accident when doing reflash experiments mine weren't tied up Dealer did not know what they were for thought maybe for brake control but he was wrong . Mine are green & orange maybe lighting makes yours look brown & green.

Those 2 wires (green and brown) with the red tie are my leads to the 2 switches I have installed on the dash for the the 2 high idle levels.

I would like to figure out exactly where to attach them to get the fast idle speeds to work without frying my PCM.

Maybe someone else did the same thing. Does the PCM in the picture look like your PCM? Are all the wire slots in your middle pigtail filled and can you trace where the other leads to your switch go to? If you get high idle by touching the bar then that would be grounding them out. The other wires at the switch must go back to the PCM but where?

Looks like same PCM should not be much difference between 98 & 99 model year, dig around the wires may be there already center plug top row pin 7 & 8 just to right of pink wire is where mine are coming from, you may need a schematic to be 100% sure. 1st pic is upside down

May want to try a touch test end of the wire to the frame rather than a switch which will take a little more time to switch off, if you are concerned about frying PCM find someone with a 99 manual & schematics double check, or wait until someone else confirms what I wrote.

Thanks Tim!
Yours is the the same as mine if your High Idle wires are the two odd wires in the pigtail (yellow and Brown or Tan). They would correspond to the 2 slots(7 & 8 on top row) currently unused in my middle plug on the PCM. Are those your 2 fast ilde leeds?

Also I was waiting for some guidance, but was going to test the voltage at the leed on the PCM using the frame as a ground then if the voltage is low touch the frame to see if there is an rpm change.

I have the set of 99 GM manuals but found no reference in the index to the PCM, but I will have to go back and check through the electrical schematics. Maybe GM uses another name to reference the PCM? Any ideas on what else it could be called?

Thanks for your pics and advice. It makes me think I am on the right track.

Thx,
John

Yup those are the 2 should be same 98 & 99, in GM manual may have to look more than 1 place in the manual, they hide stuff on you look at the actual pin out for that center plug, I recall finding it once but darned if I think I could find it again.

Thanks all!
Project was successful and finished! Yup the schematic is under the "engine controls" section of the manuals.

The only difference to the Kennedy instructions is the #7 & 8 pins are on the middle pigtail at the top of the PCM - as it sits in the vehicle behind the glove box. The pins have a full charge of 13.8 volts when the vehicle is running and somehow the voltage drops to 0 when grounded and nothing gets fried.

The high idle setup is nice in cold weather and like all other things I have done I could do it in a snap the 2nd time round.

THX,
John

Oh one last thing I forgot for anyone else who is going to try this.

Here in Saskatchewan I went to two different GM dealers with the part number for the pin connection (p/n12089649). They looked at me like I was from Mars!

So if you run into the same problem and you have access to old computer parts (floppy disk drive or 12 volt power suppy) the female side of the wire fittings are similar enough to work fine. In fact they will already have a wire attached and all you have to do is solder the wire to your switch leed. Use a set of pliers to crack open the plastic link on the old female side of the computer connector to get the wire and pin ends you will need.

I get my terminals from Auto Electric Service.

Don't know how everyone else did theirs, but I have all three idle speeds available on mine. I have two switches. The first is a single pole double throw (SPDT) switch that takes the common, and switches either the first high idle pin, or the other. The second switch shorts both together for the highest idle. It's handy for quick warm up with the two lower idle speeds, and great for A/C in the summer time (haven't tried it yet).