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Premium Member
'08 TrailblazerSS
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Discussion Starter #1 (Edited)
FUNCTIONALITY

Park Lamps as DRL at 100% duty cycle (full intensity).

Fully functional auto headlamps.

When the headlamps are commanded ON, either automatically or by the headlamp switch, the fog lamps will automatically turn on and cannot be switched off via the fog lamp switch.

With the IGN in RUN and headlamps OFF, the fog lamps can be switched ON and OFF via the fog lamp switch.

Headlamps and Fog Lamps will stay on when the High Beams or Flash-To-Pass are activated.

Fully functional perimeter lighting at 100% duty cycle.

Healamps On indicator, Fog Lamps On indicator, and High Beams On indicator all fully functional.


Video demonstrating functionality. (and yes, I know my truck is filthy and windshield is cracked lol)
http://www.youtube.com/watch?v=m0_t1EhOkiI


PARTS NEEDED

(1) Double Pole Double Throw Relay $10.49 @ Radio Shack
(1) HDM Relay (This is in addition to the factory HDM relay at the underhood fuse block. This 2nd HDM relay will be used at the Rear Fuse Block)
$34.99 @ O'Reilly's BWD
$39.99 @ Autozone Duralast (It says blower motor relay on website but this is correct part)
$34.99 @ Advance Auto BWD
$25.79 @ RockAuto ACDelco Part #15016745
(3) Diodes @ Radio Shack
(1) 10uf 35v Capacitor $1.49 @ Radio Shack

You will also need wire, various crimp connections, t-taps, heat shrink and solder depending on how you want to make your connections. For my
installation, I used t-taps, male and female spade terminals, male and female bullet connectors, uninsulated butt connectors, ring terminals, and heat shrink. I used AWG 18 wire for all connections except for 2nd HDM relay pins 2 and 4. These two connections require a larger wire. I used AWG 12 which is probably a bit overkill. AWG 14 should be sufficient.


SCHEMATICS

I'm going to post two schematics. The first one is of the stock, unmodified wiring, and the second will be of the modified wiring. This way you will be able to compare the two schematics to see what is being modified. Don't be intimidated by the schematic, it looks far more complicated than it really is. A lot of what is shown in the schematic won't be modified. I included everything to show the entire system as a whole and how it all works together.

Stock


Modified



PINOUTS

BCM Connector 1 (GY)




BCM Connector 2 (TN)




INSTRUCTIONS

These instructions assume that all wiring is stock and unmodified. If you have any DRL modules or any other modifications to your wiring, remove all modules and return wiring to stock before beginning with installation.


PREP THE RELAYS FOR INSTALLATION

1. Tape both relays together as shown in pic below.


2. PREP THE CAPACITOR
A. Connect a short piece of wire to each side of the capacitor. I used uninsulated butt connectors and heatshrink.
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B. Apply heatshrink over butt connectors.
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C. Apply heatshrink over capacitor. Make a note of which side is positive and negative. I used different colored wire. You can also tie a loop in the wire that is attached to the negative side.
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D. Attach male spade terminals to both ends. Capacitor is now ready for installation.
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We now need to build 3 sub harnesses, the HDM Control harness, the Diode harness, and the Ground harness. In the pictures of the 3 harnesses below, you will see numbers next to each connector on the harness. Later on in the installation, I will reference a harness and connector number (ex. Diode Harness-3). Just refer to the picture of the harness referenced and find the connector number. This way there will be no confusion as to which connector I am referring to.

3. HDM CONTROL HARNESS
A. Build the HDM Control harness as shown below.
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4. DIODE HARNESS
A. Attach wire to each side of the 3 diodes just like you did with the capacitor. Make sure to note which side the silver band on the diode is facing. Diode orientation is critical.
B. Build the Diode harness as shown below.
__


5. GROUND HARNESS
A. Build the Ground Harness as shown below.
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Now that you have all three sub harnesses built, they can all be attached to the relays.


6. CONNECT DIODE HARNESS TO RELAY
A. Connect Diode Harness-1 to Pin 3 of the DPDT relay.
B. Connect Diode Harness-2 to Pin 1 of the DPDT relay.
C. Connect Diode Harness-3 to Pin 2 of the DPDT relay.

7. CONNECT HDM CONTROL HARNESS TO RELAYS
A. Connect HDM Control Harness-1 to Pin 4 of the DPDT Relay.
B. Connect HDM Control Harness-2 to Pin 5 of the 2nd HDM Relay

8. CONNECT GROUND HARNESS TO RELAYS
A. Connect Ground Harness-1 to Pin B/8 of the DPDT Relay.
B. Connect Ground Harness-2 to Pin 6 of the 2nd HDM Relay.
C. Ground Harness-3 will be connected in step 26.


Now that all 3 sub harnesses are connected to the relays, there are 3 more seperate wires that need to be connected to the relays.

9. Connect a larger wire to Pin 4 of the 2nd HDM Relay. Leave some extra length. Once relays are in vehicle, you will cut the other end of this wire to the appropriate length, install a modified fork terminal, and insert into Park Lamp Relay Position 87 at the rear fuse block.

10. Connect a larger wire to Pin 2 of the 2nd HDM Relay. Leave some extra length. Once relays are in vehicle, you will cut the other end of this wire to the appropriate length, install a ring terminal, and connect to the B+ Post at the rear fuse block.

11. Connect a wire to Pin A/7 of the DPDT Relay. Leave some extra length. Once relays are in vehilce, you will cut this wire to the appropriate length, and tap into a fuse for IGN voltage.


Now Relays are ready for installation

12. Determine where you want to put your relays and place them there. I put mine underneath the BCM.

13. Now locate the BK/WH wire at BCM X1-A4 (Gray connector, Pin A4). Install a T-Tap onto this wire.
__


14. Connect Diode Harness-6 to T-Tap shown in step 13.

15. Locate the PK wire at BCM X2-E7 (Tan connector, Pin E7). Install a T-Tap onto this wire. Notice the optional piece in the picture. I cut the PK wire in my truck on a previous install and reconnected using male and female bullet connectors. Instead of putting the t-tap directly onto the PK wire, I made a small piece to go in between the bullet connectors and installed the t-tap to this piece. If you don't want to cut the PK wire, you can install the t-tap directly on the PK wire. Or you can cut the PK wire and install the optional piece that is shown in the picture. Either way will be fine.
__

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16. Connect Diode Harness-4 to T-Tap shown in step 15.

17. Locate the D-GN/WH wire at BCM X2-E11 (Tan connector, Pin E11). Install a t-tap onto this wire.
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18. Connect Diode Harness-5 to the T-tap shown in step 17.

Diode Harness should now be fully connected.

19. Locate PK/WH wire at BCM X1-A5 (Gray connector, Pin A5). Cut this wire. Install a Female Bullet connector to the BCM side of the PK/WH wire and a Male Bullet connector to the Harness side of the PK/WH wire.
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20. Get a 6"-12" piece of wire and install a Female Spade connector on one end and a Male Bullet connector on the other end.
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21. Get another 6"-12" piece of wire and install a Female Spade connector on one end and a Female Bullet connector on the other end.
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22. Get the piece you built in step 20. Connect the Male Bullet connector of this piece to the Female Bullet connector installed on the BCM side of the PK/WH wire at BCM X1-A5 shown in step 19. Connect the Female Spade connector of this piece to Pin 6 of the DPDT Relay.
__


23. Get the piece you built in step 21. Connect the Female bullet connector of this piece to the Male Bullet connector installed on the Harness side of the PK/WH wire at BCM X1-A5 shown in step 19. Connect the Female Spade connector of this piece to Pin 5 of the DPDT Relay.
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24. Install a T-tap to the piece you installed in step 22, as shown in the picture below.
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25. Get the capacitor. Connect the Male Spade connector on the positive side of the capacitor to the t-tap shown in step 24.
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26. Connect the Male Spade connector on the negative side of the capacitor to Ground Harness-3.
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27. Locate the wire you connected to Pin A/7 of the DPDT relay in step 11. Route wire to the fuse shown below at the rear fuse block. Cut wire to the appropriate length and insert wire and fuse into fuse block. You can use a fuse tap or just smash the wire and the fuse into the slot like I did. Make sure when you tap this fuse, you tap the side of the fuse shown in the picture. If you tap the other side of the fuse, the wire will not be protected by the fuse.
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28. Locate the Park Lamp Relay at the rear fuse block.
__


Remove the Park Lamp Relay. It will not be used.
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29. Route HDM Control Harness-3 to the park lamp relay location. Cut wire to appropriate length. Install modified fork terminal. Insert into position 86 of the Park Lamp Relay Location.
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30. Locate the larger wire you connected to Pin 4 of the 2nd HDM Relay in step 9. Route this wire to the park lamp relay location. Cut wire to the appropriate length. Install modified fork terminal. Insert into position 87 of the Park Lamp Relay Location.
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31. Locate the larger wire that you connected to Pin 2 of the 2nd HDM Relay in step 10. Route this wire to the rear fuse block B+ Post. Cut wire to appropriate length. Install a ring terminal onto the wire. Attach wire to B+ Post.
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32. Route Ground Harness-4 to the rear fuse block just below the B+ post. Connect Ground Harness-4 to ground using the rear fuse block mount just below the B+ Post.
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33. That's it! Now verify that everything works properly.
 

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Premium Member
'08 TrailblazerSS
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Discussion Starter #3 (Edited)
I'm a tech for a company that services displays in retail stores. The main display we service is the Walmart Car Audio display.

 

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Registered
2008 TrailblazerSS
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282 Posts
Excellent write up and photos!
 

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Too fast to be so slow.
TrailblazerSS
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3,356 Posts
Nice write up. Its nice too see people that are not in electrical related careers tackling projects like this. Its not too difficult if you brake it down.

By the way, your truck is filthy and your windshield is cracked....
 

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making friends daily
07 TrailblazerSS AWD
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9,331 Posts
You are the man! I know Brandon's been more than helpful with me lately! :cheers1:
 

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Premium Member
'08 TrailblazerSS
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2,987 Posts
Discussion Starter #11 (Edited)

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Willy M'Fn Wonka
07 Trailblazer SS
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7,244 Posts
Thank you Brandon. Bout fucking time someone actually did this (and wrote instructions)!!!

This is the best lighting set-up functionality that we can have, bar none.

** If we wanted to use "switchbacks" in both locations (horizontal & vertical) of the parking lights...would anything need to be changed??**

PM sent.
 

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Premium Member
'08 TrailblazerSS
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2,987 Posts
Discussion Starter #14
Thank you Brandon. Bout fucking time someone actually did this (and wrote instructions)!!!

This is the best lighting set-up functionality that we can have, bar none.

** If we wanted to use "switchbacks" in both locations (horizontal & vertical) of the parking lights...would anything need to be changed??**

PM sent.
I don't think anything would need to be changed but I'm not 100%. Send me a link to the ones you want to use, or are already currently using, and I'll take a look and see if anything needs to be done and then let you know.
 

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Registered
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155 Posts
Great write up. Sadly I did something wrong installing this. All the auto functions work, fog lamps, and quad beams, but my headlights are still acting as DRL. Did I install a diode in the wrong spot or backwards?
 

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155 Posts
:coolthumb:Well, thanks the the great help from Banndon, turns out it was wired correctly, i just had a bad relay. I assumed i messed up and didn't verify it was switching. Checked continuity and found the coil open. Another great example of a fabulous contributing member to the forum. Thanks for the help Branndon.
 

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Premium Member
'08 TrailblazerSS
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2,987 Posts
Discussion Starter #18
No problem.:cheers1: Good to hear everything is working.
 

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TrailblazerSS
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377 Posts
I just competed this after removing a DRL killer ONLY and everything works great but my new DRL parking lamps are not coming on at all when in gear? I haven't dug into the harness yet but which wires control this?
 

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05 TrailblazerSS AWD
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666 Posts
So I need to take my DRL killer out before I do this mod??
 
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