Turn directional wiring in the door of an 2004 XL

XL Envoy

Member
Newly joined the forum and my first post.

I had to replace a driver's door mirror. Truck was not built with the mirror turn directional signals. So what the hell, time for an upgrade. If I can do the driver's side, I will do so for the passenger side.

I did find a Light Blue wire in the door leading to the DDM. This flashes my trouble light with the left turn directional. A11 is the connector. However, I am not sure of the ground for the lamp. Anyone know of the ground? For some foolish reason, I want to try and do this correctly.

Thanks!
John
 

Blckshdw

Moderator
If you buy mirrors with the turn signal bulbs built in, they will be plug and play. You'd only have to deal with the wiring, if you were adding turn signals to the plain Jane mirrors that only had mirror glass adjustment.
 
OP
OP
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XL Envoy

Member
That is the exact issue. The truck was supplied with the Plain Jane version mirrors so I have to tap the door's harness somewhere. That is why I was hoping someone had familiarity with the DDM and the in-door wiring.

I have spent a lot of time searching the Internet already. If I find something, I will post it.

Edit- I had found yesterday a posted GIF with some wires. It shows the Light Blue as "Left Turn Signal Lamps Supply voltage" at A11 just like the wires to my DDM are. But, it shows a Gry/Blk wire as "Left Turn Signal Lamps Supply Voltage" at A2, and that is not the same as my DDM's wires. I do not know if that is the ground or something else. The wire at A2 doesn't flash my troublelight like it does at A11.

I did try to find a ground the other day with a multimeter. And some of the lines which looked like grounds woke up and were no longer "connecting" when I started the truck up and checked again. So I figure some of those are bus lines or similar.

Ya gotta love that name- "Left Turn Signal Lamps Supply Voltage". I guess I need to go for training to remove a lot of brain cells for stuff like that to make sense.

Thanks, John
 
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Blckshdw

Moderator
I had the same setup, and wanted to do the same modification you're doing (and some other stuff)

All of the necessary wiring is already in place, the PDM and DDM decipher the incoming signals from the stalk, and the outputs on the door modules where the mirrors plug in will have the connections for the bulb. Your plain mirrors just have empty pins right now, compared to what will come with the turn signal mirrors.

So in short, buy your new mirrors, install em, and enjoy. No need to overthink it. :thumbsup:
 
OP
OP
X

XL Envoy

Member
Dang. I guess I have a bad DDM or PDM then. I had installed the new mirror, and when the turn signal didn't light up I figured I was missing wiring. The motors position the mirror properly, it is just the directional that won't work.

Ah, well. Thanks for your time!
John
 

Blckshdw

Moderator
Ahh OK, now things make more sense. Well since you found the turn signal wire already, you can use any black wire in the same wire harness as the ground, and that will work.

I tried to find the write up on the other site, that I know had pics of which harnesses and wires to tap into, but couldn't track it down. 😥
 
OP
OP
X

XL Envoy

Member
Thanks to both Mods! I will see if I can ultimately get this done. Have to outwait the heavy rains before examining the wire color codes.

More to come.
John
 
OP
OP
X

XL Envoy

Member
Well, Kiddies, after a bit of poking about the turn directional now works. Has been working now for several days. As I was using a meter to read contacts, as part of this I added a temporary ground to the existing. As soon as I did, the turn directional started to work. Removed it, it still works. Temps have varied from below freezing to mid 60s, I don't think it is a poor ground.

I will assume not that the ground was bad but that the DDM possibly needed to learn it was there. I feel that when I added the second ground which was a heavier cable, the DDM saw a change in state. I had to reteach the DDM the passenger window Open and Closed states afterwards which is why I wonder if the DDM was involved.

Either way, it works.

Side rant- DigitalVoltMeters lie. They are like politicians. It depends on how you interpret their results whether you can trust them. DVMs use a very small current to read resistance. The older Analog meters with their fragile needle pointers use much more current and are much better indicators for testing contacts and wiring. As a tech working with low voltage wiring, telephone circuits, computer LANs and so on for decades, I have seen circuits test "good" that do not work as they cannot carry any current. With the proliferation of all the sensors and additional wiring and connectors, I often wonder if people are chasing symptoms of marginal connectors and/or bad harnesses and that is why replacement parts don't fix issues. Or identical issues return. Decades ago, the burglar alarm guys had "Peter's Meter" which wasn't really a meter, but a t-shoot unit that had a relay. As you went around trying to find a bad connection, the relay would latch the trouble indicator so that you could see it failed, even momentarily. You would insert it at the alarm panel and then could go through all the windows on various floors, stopping to check it every once in a while. When windows heated up back in the copper days, it was common for one window to develop a hairline crack. when it got cold, it would send a false alarm. I use my Fluke digital all the time but as soon as I come across something I stop to think about, if I can I use my old Simpson. It has saved me many days worth of troubleshooting and recalls. Wonder if I should create long leads with insulation piercing clips so I could then bypass the connectors. I did clean the DDMs pins earlier in my t-shooting.

Regardless, with the driver's side directional working, I also ditched the original passenger side with a turnsignal equipped one. Then moved into replacing dead lighting in the door switches, now moving into the dash. The only other issue is a broken actuator in the Heat/AC unit in the back. It will be a bit of time before I can tackle that one.

Thanks,
John
 

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