DIY Flip the Tow harness for 2021 tundra (fixes 'disconnect')

EDIT: Post 4 has links to better connectors

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My 2021 Crewmax constantly loses the trailer connection when driving - any small bump results in "Trailer Disconnected." That in turn is because the Toyota engineers mounted it _sideways_ instead of upright. The weight of the cable then pulls out the plug rather then causing it to cam against the little tab on the lid of the connector.

Anyway, there are already many threads on how install the Hopkins connector:

$47 Hopkins Towing Solutions 43395 Plug-In Simple Vehicle to Trailer Wiring Kit

https://www.amazon.com/dp/B004BE7WN4?ref=ppx_yo2ov_dt_b_fed_asin_title

For most people it's plug & play - unplug the old one, plug in the new one. Hardest part is deciding where to mount it!

However on the 2021 those plugs under the vehicle have been deleted! In fact that year has a host of other things missing as well compared to the previous gen - mainly cupholders, pockets - dual zone climate control etc. (I'm sure the latter has moved to a higher spec, I have the SR5.) Deleting the plug probably saves toyota 50 cents.

Decided to cut the Hopkins plugs off and same with the Toyota side. Next challenge: Toyota wired the color coding differently! Watch any YT video for trailer wiring and they won't help you - ha ha! Luckily the hopkins comes with a wire diagram and the _old_ toyota plug also has a little diagram embossed right on the lid! For good measure I also tested each wire prior to connecting them (had my wife run the controls on the truck and I used a multimeter.) PSA: Use 'AC' mode on the multimeter to check the turn signals, at least you get a non-zero reading. The rest are DC mode.

Here are some pics of how it turned out. I used the factory bumper hole for the Hopkins and cut the old connector in half to use as a plug for the gap. It looks like the OEM Uhaul connector is still present, but I have it glued shut. The Hopkins has a little Uhaul plug on the left side anyway so no functionality is lost. I could have fabbed a small metal plate or something but this was easier at the time and still looks somewhat "OEM" (or ghetto...maybe!)

It seems to have worked. The trailer cable remained secure last time I towed. Will report back if I ever have any issues.

Hopkins Plug side
- This will match all YT videos
- (After Hopkins grey Toyota connectors chopped off)


Toyota plug side
- This matches nothing in the universe, including wire colors
- Looking from back of truck toward the world, just showing wire colors
- This piece was previously connected to outside connector
- It get discarded


Spliced connections
- I soldered and heat shrunk
- I did remove a couple zip ties under the truck to allow the OEM wire harness some more wiggle room. This let me work outside the truck rather than under it!


Connection map
- Parenthesis = Toyota
- Square outline = Hopkins
- View looking toward the truck into the 7-pin plug


Final Result

 

I was towing last week and kept having the same problem with the CONSTANT in/out trailer disconnected alarm. So obnoxious. I didnt even think to blame the truck I just assumed it was the trailer plug since I was using my dads enclosed trailer that I don't tow very often. It seemed to fit snug enough too but now I may need to dig a little further. Have you had success towing with the new setup and no alarms? Great writeup otherwise, love the clamp to hold the wires up too and the solder job!

 

Haven't towed more then 10 miles yet but we have a trip coming up next week. Will post after that.

 

To hopefully save others some time and effort:

The connector quoted above is a USCAR connector, while the wire colors might not match across brands, the pin out is the same across all brands. You can pick up any USCAR 7 pin socket and plug it right into that if you are looking for an upgrade or replacement. No need to test wires with a multimeter or cut anything.

https://www.curtmfg.com/towing-electrical/original-equipment-replacement-connectors/learn-more

Examples:
https://www.etrailer.com/Trailer-Wiring/CURT/C55416.html
https://www.etrailer.com/Trailer-Wiring/CURT/C42JR.html
https://www.etrailer.com/Custom-Fit-Vehicle-Wiring/Hopkins/41157.html

 

Awesome info pman9003, thanks!

Anyway, the result of 'flipping' the plug was indeed beneficial. Towed 150 miles round trip and not a single disconnect.

I've noticed some other brands use the same plugs as the Tundra but they're correctly mounted in vertical orientation. I'm sure Toyota had some reason for doing it wrong, likely to save space on the bumper. But they didn't do it to make towing more reliable, that's for sure.

 

This... no reason to cut wires. It actually looks like the C42JR will fit the factory mounting location.

My OEM plug has the same issue with disconnecting. I wish I could remember what it was called, but I used a plastic strap with a threaded knob around the plug and door. Tighten it up and it never comes loose. I might have to give another plug a try.