2003 Yukon XL/8.1l Under hood ignition hot source?

[woytovich]

I'm installing an aux fuse box under the hood and would like to get an ignition hot source for 12v to use to trigger a couple relays... Is there any good/known/reliable source for that under the hood?

Thanks,
Mark

 

[Sub]

Yes. There are many Ignition hot circuits under the hood... most of which can be found underneath the UhBEC... "Underhood Body Electrical Center"... basically, the power distribution center, aka the main fuse box.

Remove negative lead off of battery, cover negative battery terminal, and wait 10 minutes.

If you unfasten that fuse box and turn it over (as best as you can, it is hard to turn with all the wires attached) you will find an overwhelming amount of ignition hot wires. They are all known to be good, otherwise the car wouldn't run!

You will notice right away that the many, if not the majority of wires that are PINK in color. Generally speaking, pink is the color GM most often uses for ignition hot circuits on our GMT800 vehicles. GM's term for these pink wires is "Ignition 1 Voltage."

A wiring diagram for your year, engine, and options is STRONGLY RECOMMENDED. I have a 2500 YXL similar to yours, but I have a different engine, and different electrical options, so the circuit arrangement in my UhBEC might differ from yours. With that being said, I found Ignition 1 voltage in 19 different cavities within the first 2 connectors alone, and there are 9 connectors under the box.

Connector C1: Cavities A6, A9, D10, F1, F5, F6
Connector C2: Cavities A9, A12, B9, B10, C10, D8, D9, D10, E6, E7, E10, F8, F9
Connector C3: (anyway, you get the idea)

The presence or lack thereof of Ignition 1 in these cavities is very much equipment and option dependent. The wiring diagrams indicate the RPO codes where these circuits might be expected to be found in.

Then, it will take personal judgement to decide what kind of load you are adding, and what components are already on the circuit you are sharing that might be affected by your addition. i'm assuming you are just adding a trigger voltage relay, which isn't much of a load, but all the same I probably wouldn't chose to splice into the Ignition 1 source to say, the ABS module.

A few years ago, I needed an ignition hot to trigger a factory relay that I added for a second battery. After considerable thinking about which Ignition 1 source to splice into in the UhBEC, I ultimately decided to follow the factory wiring diagram for RPO code TP2 exactly, which involved passing a new Ignition 1 wire from the LhBEC (Left hand Body Electrical Center) under the left hand side of the dash inside the cab, through the fire wall, into the UhBEC. Seemed kind of silly, and was no doubt unnecessary, since there were SO MANY Ignition 1 circuits to chose from that were already RIGHT THERE, but I wanted the factory circuits I added to exactly match the diagram in that instance.

 

[woytovich]

Great info.... JUST what I was looking for.

Thanks,
mark

 

[iceworm]

... A wiring diagram for your year, engine, and options is STRONGLY RECOMMENDED. ....

Sub -
Great post. Informative and clear.

Do you have a recommendation for where to find a set of vehicle specific wireing diagrams? Definitely something I could use. And, no, I don't mind paying -

worm

 

[Sub]

Sub -
Great post. Informative and clear.

Do you have a recommendation for where to find a set of vehicle specific wireing diagrams? Definitely something I could use. And, no, I don't mind paying -

In the case of your 1999 model year, the official resource (Helm, Inc) for wiring diagrams listed and recommended by GM in the vehicle's Owner's Manual is unfortunately out of stock at the moment. Helm invites interested parties to put their name on their email list for automated notification of when stock is replenished. This is for the paper version of the service manual set, which includes the wiring diagrams. Here is the link:

http://www.helminc.com/helm/product2.asp?Make=CHV&Model=TAHO&Year=1999&Category=1&class%5F2=CHV&mk=Chevrolet+%26+Geo&yr=1999&md=Tahoe&dt=Shop%2FService+Information&module=&from=result&Style=helm&Sku=GMT99CK&itemtype=N


The method above is how I used to obtain paper service manuals in the late 70's and 80's, per the Owner's manual suggestion. Then, in the mid 90's, I began ordering manuals on CD Rom, then DVD rom, and then.... on eBay. Once I went to eBay, the cost for service information reduced 50-100 fold. Then, in the mid 2000's, that open spigot got shut off.

Now, it takes tenacious searching online, but most wiring information, especially on older models, and especially relating to common problems, can be found online for free. By the time a vehicle is 16 years old, someone, somewhere, has had the same problem and pounded it into submission, and then posted a victory flag to help others, in the form of a wiring diagram that they scorched the earth to obtain.

I keep antivirus programs on full alert, and disable Javascript when hunting for wiring diagrams. There are many questionable websites out there that specifically index key word search terms like 1999 Chevrolet Tahoe Wiring Diagrams... and they will be on the first page of google hits with pdf files waiting to download. I don't trust what comes with that kind of download.

Using "google IMAGE search" appears at a cursory glance to bring up plenty of diagrams... not the entire set, but perhaps the page that you need is the same page that someone else posted in the process of sharing their resolution to a similar issue.

Haynes, on the other hand, is quite different than Helm. Haynes should not be relied upon for anything but the most basic of tasks. And Haynes wiring diagrams are not specific enough to be accurate or reliable. One cannot compress 1,200 pages of service information spread over several 2" thick volumes... down into a 1/2" thick auto store pamphlet, half of which describes how an internal combustion engine works and what an alternator does, amounting to the same text that is repeated in every Haynes manual. That is a far cry from the kind of vehicle SPECIFIC factory service info that the factory service manuals available from HELM provides.