How to: Dome Light Switch to Engage High Idle - Diesel Place : Chevrolet and GMC Diesel Truck Forums
 
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Third Generation Duramax Electronics/Tuners Discuss 2006-2007.5 LBZ & LLY Duramax engine electronic upgrades including chips, tuners, programmers, etc.

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Old 11-21-2015, 01:34 PM   #1 (permalink)
jd4230
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How to: Dome Light Switch to Engage High Idle

I couldn't start a DIY thread, so Admins move it if you need too. This is my first DIY so if you have any thread starting tips, let me know. This DIY is meant to give you an option for engaging the High Idle feature of your Duramax by using the Dome Light Cancellation switch. I wanted to add the high idle to my truck, and I wanted to use an existing switch in the dash for a cleaner install. Thanks to Captain91 for the idea.

This is for '03-'07 trucks, and I believe it will work on the '01-'02's, but I don't have access to one to see the dome light cancel switch. My dad has an '08, and I haven't looked to see if that truck even has a dome light cancel switch. There are many good high idle mod DIY's out there, so I will assume the under hood portion of your install is done.

This is what I used. LBZ High Idle Install with Pics - Diesel Place : Chevrolet and GMC Diesel Truck Forums

You need to have access to 12v power. I chose the SEO ACCY fuse in the driver's side fuse panel and used a fuse tap. You just need a 12v signal, hence the 2 amp fuse. I couldn't find a 1 amp as that would be fine too.
SEO ACCY.jpg

Here is how I have the layout for the 12v power coming from the truck. Its split into two wires to power the 12v relay. One lead for the #86 post and one for the #30 post.
Fuse.jpg

A 12v relay needs power, usually from a low current circuit that you control with and on/off switch, and ground to "switch" a high draw circuit, such as driving light. Well, on these trucks, the dome light cancel switch is actually a switch to ground. So by pushing this switch, you provide ground and the dome lights go out. I used it to provide a ground for the relay when it's pushed, which then provides the 12v signal to the ECM for the PTO high idle functionality. The green wire is attached to the purple wire coming out of the back of the headlight switch assembly and is attached to post #85 on the relay. Pin #87 is attached to your 12v power lead that routes to the ECM.
Purple Wire.jpg

Dome light cancel and headlight assembly.
Dome Light Switch.jpg

This worked just like I wanted except I was getting a back feed that permanently turned on the radio and the instrument cluster lights. I then added a diode to the switched grounding wire and this solved the problem. I soldered and heat shrunk the wire before I took the picture so I stuck another diode in so you could see the direction it needs to be. The gray line on the diode is away from the relay. In the picture, the 2 yellow wires are ignition on 12v positive going to pin #'s 30 and 86. The white wire goes from pin #87 to the ECM. And the pin #85 has the diode and is tied into the purple wire in the connector on the back of the head light switch assembly.
Relay Wiring.jpg

Here is a video of how it works:

http://www.youtube.com/watch?v=R0bV84BJwJU

Have fun!

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Old 04-09-2016, 09:52 PM   #2 (permalink)
jd4230
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It's April 9th and I used this today because it was 25 degrees this morning! And I'm in central Illinois.

'07 GMC LBZ CCSB

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2007 GMC SLT Classic, 2500HD CCSB
Edge Insight CTS w/EGT Probe
EFI Live w/DSP5 switch by Duramaxtuner.com (Nick)
Pullrite Superglide 5th Wheel Hitch / DMI Quic 'n Easy Receiver Hitch
Transgo Jr./Allison Filter Lock
HD SynTran Tranny Fluid (John Deere's Syndtran) Mike L. Transmission Cooler
Diesel Race Parts replacement Tranny Cooler Lines
Leveled Tow Mirrors
3" AFE Down Pipe & 4" AFE DP back SS exhaust
18" x 9" Ultra Predator 8 Wheels / Cooper Discover AT3 275/65 R18 Tires
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