I always seem to have "something" plugged into my truck, be it a Tech 2,
EFILive, ELM data bus interface, whatever. I finally got sick of having
the plugs bumping into my leg, in the way, tangled cords going over the
steering column, etc...
So I decided to wire up a second DLC on the passenger side. That way I can have the laptop sitting in the passenger seat like I usually do, except just plug in EFILive right there so its convienient and I dont have cords going everywhere! I dont know why I didnt think of this before...
This is a pretty easy mod, and doesnt even require that much wiring. The best part is, you dont even have to run wires all the way over from the original (driver side) DLC (data link connector, same thing as ALDL, OBD port). This because you can pickup ground right on the dash frame, and +12v power from the junction block on the passenger side of the dash, right under that snap-off cover (where the drivers side fusebox is, except on the pass side). Also, because the Class 2 data bus wiring is common and integrated throughout the entire vehicle, you can also tap into a data wire in that same junction block, so the wiring to the second DLC is less than a foot long...no snaking wires etc...
2. couple small bolts and nuts (I used some old stove bolts I had lieing around)
3. DLC and pins. This can be found on ebay, or if you do a Google search, there is a site that sells them, 1 connector + pins is 7 dollars plus shipping.
5. soldering iron
7 electrical tape and/or heat shrink tubing
8. crimp ring terminal
You can also use the scotch-lock connectors, or crimp terminals, but I always like to solder things.
1. empty all the stuff out of your glovebox and flip it all the way down by pressing in the retaining tab. Find a location to mount the DLC, I mounted mine vertically to the lower-most metal portion of the dash support, where the glovebox assy screws in. You can mount it anywhere tho. Test fit it with the Flashscan cable attached to make sure its going to fit properly and is easy to unplug and plug in. I didnt test fit it with my bulky Tech 2 plug, so only the EFILive plug fits, but oh well, I can always move it in the future.
2. drill holes thru the lower dash assembly and glovebox hinge as shown at the proper spacing to mount the DLC.
3. Test fit the DLC to make sure all the bolts line up, etc.
4. Cut 3 lengths of wire, about a foot or so long. I used different colors to make it easier to wire.
5. strip the wire and crimp the DLC pins onto the wires. I just used some snub-nosed pliars and crushed it in a bunch of different ways...just crimp it enough to squish everything down tight and so the wires wont come out. You will actually need a 4th pin crimped to an extra ~3" long wire. This is because there are two ground pins at the DLC, dont ask me why. You can solder the short pigtail onto the main ground wire close to the plug.
6. Solder the two ground wires/pins together as shown.
7 insert the pins into the DLC as shown. Pin 2 is Class 2 data. Pins 4 and 5 are ground. Pin 16 is +12v power. I used red for +12v, black for ground, and green for Class 2 data.
8. Twist the power and Class 2 data wires together, just to make it neater and cleaner. Class 2 is so slow (10.4kbps IIRC) and robust that you arent going to get any interference by twisting it with a power wire.
9. cut the ground wire shorter, maybe 6". This is because you can just tap the ground wire into the metal dash support that the DLC is bolted to.
10. Strip the ground wire and crimp on the little ring terminal. Make sure the ring terminal is big enough that your DLC mounting bolts fit through it.
11. Bolt up the DLC and slip the ring terminal over the bolt as well before you put the nut on. Tighten everything up. You can check to make sure you have a good ground with a test light or multimeter. Touch one probe to pins 4 and 5 on the DLC and the other probe to any ground on the truck, the dash frame, door, whatever, and see if you have a good ground.
12. Run the two power and data wires behind the glovebox support and around to the passenger side junction block as shown.
13. Strip the ends of the wires and unplug the white/light brown plug from the junction block.
14. Find the small orange and tan wires in that connector. Orange is +12v and tan is Class 2 data. Splice your power and data wires from the DLC into the appropriate orange and tan wires on that connector. Obviously dont cut the wires, just tap into them. I soldered everything up and taped it up with electrical tape. See picture...
15. Clean everything up, plug the connector back in, make sure nothings loose, etc...
And thats it...plug your Flashscan into the DLC and see if it lights up, also check to make sure the data light flashes, indicating the data wire is hooked up properly. The DLC is fused as well, because that wire coming out of the junction block is fused. I dont know which fuse though, probably the PDM fuse. You're done.
Couple important notes:
1. This mod applies to 2003-2005 trucks only. I dont know if the passenger side junction block wiring/wire colors/connectors are the same on 2001-2002 trucks. If you are not sure on your 2001-2002 truck, you can always just run the power and ground wires over from the original driver side DLC.
2. This will not work for 2006-2007 LBZ trucks. The LBZ ECM and 4th gen Allison TCM only communicate to the outside world with high speed GMLAN. The GMLAN wires only go to the DLC on the driver side. If you want to do this on an LBZ, you will have to run the GMLAN high and low wires (there are two) from the DLC on the driver side. Make sure you twist these wires together, as GMLAN needs to be run on twisted pair wire. The orange power wire on the pass side junction block is the same as the 03-05 trucks, so you can tap into power there.
3. This will not work for 2007+ GMT-900 LMM trucks. Again, the electrical system is completely different, but as with the LBZ, you can run the wires directly over from the driver side DLC and it will work fine. The pass side junction block wiring will probably be different, so unless you find a confirmed +12v wire on the pass side junction block, you will also have to run a power wire over from the driver side DLC.
4. On the LBZ and LMM DLC's: GMLAN + is pin 6. GMLAN - is pin 14.