Towing Mirror Harness Questions

jwstewar · August 22, 2018

I've done a lot of search and reading and I keep getting more confused.

I recently acquired a 2017 2500HD with the Duramax and the exhaust brake. It came with the little DL8 mirrors. I wanted towing mirrors. So I learned the hard way about the ambient temp sensor. I've sense taken the aftermarket mirrors back off to turn the check engine light off, but on the quest to put them back on. I've ordered a kit from BoostAutoParts that will give me the ambient temp sensor, way over priced for what it is, but it will just allow me to plug the sensor into the aftermarket mirror plug.

Anyway, now for the question, I want to get the other functions (Turn signal, Park Lamp, cargo lamp) to work too since they didn't work when I originally had the mirrors on. I've seen a lot of part numbers, but that is what has me confused. I think I've either narrowed it down to one of two sets of wiring harnesses.

Left Right

84290984 84290964

84125571 84125561

Which of these sets do I need or is there another set I need?

1st diesel truck · August 25, 2018

While I didn't fully search all this out I quickly happen to run across the following linked site that offers a chart and good description down to the right of the chart that might be able to help you better as it seems pretty detailed regarding the towing mirrors.....https://www.shopgmcparts.com/trailering/2018-sierra-3500-trailering-mirror-harness-driverside-door/gm/84290984-p-7536.html

While on the same website and clicking on a 17 2500HD trailering kit offers some info it seems, https://www.shopgmcparts.com/2017-sierra-2500hd/trailering-c-82_878_906.html

Not sure if you've searched that site but if you can't find the info needed maybe it'd be worth a call.

Hope this helps some, good luck.

Edited August 25, 2018 by 1st diesel truck

jwstewar · September 9, 2018

Thought I would reply to this and let everyone know what I figured out. I did gobs and searches and after reading until my head almost exploded I ordered the 84290984 and 84290964 harnesses from GM Parts Direct. They asked for a VIN, they then sent an email saying this isn't the right item for your VIN. I had to assure them that is the parts I wanted - well, after asking them to confirm it would get me what I needed. They wouldn't do that, so I said fine, send what I ordered.

Using the kit from Boost Auto. I disassembled my after market mirror. Drilled a hole in the bottom of the mirror to insert the temp sensor in the chrome cover of the mirror. This left just enough room to not hit the inside of the mirror or the main piece that gets inserted. I then routed the wire through the mirror and followed it along the mirror harness. I then put the pins in the plug following the video directions on Boost's website.

So finally I had a chance yesterday. I took it into my buddy's garage and we tore the doors apart and ran the new harnesses. Everything plugged in perfect on both doors. The turn signals work, clearance lights work, the clear lights light up with the cargo lamp, mirrors move. So the only thing that hasn't been verified is the heat, a little too warm here to know if that is working or not. Wasn't a bad job. It took us 5 hours to do it, but that is because he had to stop and keep helping customers, I then had to run one of his customers home whose car wasn't done, and he had to take the roll-back to pick up a police cruiser that had been in a wreck, so overall working time was probably closer to 2 - 2 1/2 hours. Driver's side took longer because we had to figure out how to take the door apart.

So total cost for the upgrade $229 for mirrors from Amazon, $58 for the ambient temp sensor from Boost Auto, and ~$130 for the two wiring harnesses from GMPartsDirect. Being able to see behind the trailers - priceless. I have yet to get pictures of the mirrors on the truck, but I did take some of the mirror modification but my phone did an upgrade and lost all of the pics on the SD card, still need to try to get them back.

jwstewar · September 9, 2018

Oh, one other thing. After changing the mirror, I didn't get a check engine light, but I got a possible ice warning and the radio said it was -40. After having swapped the original mirrors back before, I knew it would take a bit. So we took the truck for a drive and after about 5 or 6 minutes the temp on the radio started going up quickly and started working fine. No issues since. Just wanted to throw that out in case any one does this and gets scared by the -40 display.

jwstewar · October 9, 2018

I was finally able to get most of the pictures off my SD card.

You can see how I drilled the hole in the bottom of the mirror. I was worried about clearing the inside, but as you can see, it worked out great. I thought I had a picture of how I had to take the mirror apart and run the wire through the arm, but maybe that was something I didn't get back.

Roper525 · March 2, 2019

I am looking to update to an OEM temp sensor in my 1aAuto mirror as their cheap sensor shows around 7 degrees off all the time. Does anyone know where I can get an OEM connector that will plug into the OEM temp sensor? Part number or link for the connector or pigtail would be helpful.

redwngr · March 3, 2019

How are you reading the temperature reading from the mirror sensor?

jwstewar · March 3, 2019

22 hours ago, Roper525 said:

I am looking to update to an OEM temp sensor in my 1aAuto mirror as their cheap sensor shows around 7 degrees off all the time. Does anyone know where I can get an OEM connector that will plug into the OEM temp sensor? Part number or link for the connector or pigtail would be helpful.

Technically if you have a pin remover, you could pull the OEM sensor and wires from your original mirror and put them into the new mirror harness. I'm running the one from Boost Auto and it is pretty darn close.

redwngr · March 3, 2019

38 minutes ago, jwstewar said:

Technically if you have a pin remover, you could pull the OEM sensor and wires from your original mirror and put them into the new mirror harness. I'm running the one from Boost Auto and it is pretty darn close.

How do you read the temp from the mirror sensor? Tech II?

On dmax, radio displayed temp and HVAC system use sensor behind the grill.

(which is why it may be necessary to run the HVAC in manual when a winter front is installed)

Edited March 3, 2019 by redwngr

Roper525 · March 3, 2019

3 hours ago, jwstewar said:

Technically if you have a pin remover, you could pull the OEM sensor and wires from your original mirror and put them into the new mirror harness. I'm running the one from Boost Auto and it is pretty darn close.

Unfortunately I have sold those mirrors months ago. Anyone have the connector part number or could send pictures? I will have to make my own pigtail but have to find the right connector first.