More 7 Wire & Trailer Brake Questions (1 Viewer)

HawkDriver · Jul 13, 2020

Yes, there are a dozen excellent threads with how to's and why for's. They're super helpful. BUT! One question remains for me:

What is this plug for? If not for a "Heavy Duty Towing Package" or something of the sort.

My 2000 has the standard 4 flat and factory tow receiver. It's plugged in above the muffler, shown here, real simple & works great. I'm picking up a travel trailer tomorrow and opted to pay them to install the brake controller and 7 pin outlet to control the brakes, but using a number of threads on MUD here I'm trying to prime the setup for the tech and run the wires out to the back where I want them. I look up and see this open plug on the driver side, could it be?! a simple pr-wired 7 pin outlet?? If not, then what the heck is it for?!

Thanks gang!

Jeremy A

ramangain · Jul 13, 2020

That goes to the dilithium crystal. You don't have one installed?

HawkDriver · Jul 13, 2020

ramangain said:
That goes to the dilithium crystal. You don't have one installed?

LMFAO!!!

And then I googled it! Now I'm wiping tears from my eyes!!!!

MJK · Jul 13, 2020

IIRC - your truck is prewired for a 4 pin connector. That includes L Turn, R Turn, Park/brake lights and ground.
A 7 pin connector adds in Aux power, an electric brake controller sending wire, and reverse lights. So, you will need to supply those lines. And, if you are buying a trailer with brakes you'll want a brake controller too.

7 Pin Towing Questions

I need to set up a 7 pin towing system on my 2001. I've read a bunch of old posts and think I know what to do, but want to confirm for my own peace of mind. Three questions, in order of stupidity, least to most: Seems like most guys have added a 4 to 7 adaptor, and then just run wires directly...

forum.ih8mud.com

7 Way Trailer Wiring Harness DIY

After looking around for a used 7 way trailer wiring harness(Toyota pn: 82177-60010, Wire Frame No. 4) and having no luck, I decided to build my own. The Toyota price of $210 + shipping was riddiculous to me for what that is. I wanted to stay as stock as possible in this and avoid cutting the...

forum.ih8mud.com

Where is trailer plug?

Here is the 7 pin on my 05 (photo taken from rear bumper, looking towards Driver's Rear tire) Wiring connects to the Driver's side plug shown in @SHOSHO 's pic above.

forum.ih8mud.com

ramangain · Jul 13, 2020

Actually, (total guess) that could be for running board lights.

gregnash · Jul 13, 2020

I tested the same plug for L/R blinkers, tail and stop lights and got nothing... Not exactly sure what it is but has no power from would I could tell.

Since you have the 4-pin already you should be able to utilize one of the Curt 4+7-pin systems. Basically utilizes the current 4-pin setup to power the 4-pin setup and the appropriate connections on the 7-pin. The rest will have to be wired by hand. I am working on it but believe my tow box has an issue in it.

HawkDriver · Jul 14, 2020

MJK said:
IIRC - your truck is prewired for a 4 pin connector. That includes L Turn, R Turn, Park/brake lights and ground.
A 7 pin connector adds in Aux power, an electric brake controller sending wire, and reverse lights. So, you will need to supply those lines. And, if you are buying a trailer with brakes you'll want a brake controller too.

7 Pin Towing Questions

I need to set up a 7 pin towing system on my 2001. I've read a bunch of old posts and think I know what to do, but want to confirm for my own peace of mind. Three questions, in order of stupidity, least to most: Seems like most guys have added a 4 to 7 adaptor, and then just run wires directly...

forum.ih8mud.com

7 Way Trailer Wiring Harness DIY

After looking around for a used 7 way trailer wiring harness(Toyota pn: 82177-60010, Wire Frame No. 4) and having no luck, I decided to build my own. The Toyota price of $210 + shipping was riddiculous to me for what that is. I wanted to stay as stock as possible in this and avoid cutting the...

forum.ih8mud.com

Where is trailer plug?

Here is the 7 pin on my 05 (photo taken from rear bumper, looking towards Driver's Rear tire) Wiring connects to the Driver's side plug shown in @SHOSHO 's pic above.

forum.ih8mud.com

Thanks MJK!

Yep, those are among the "dozen" threads I read. Can you expand on what an AUX power does for the trailer, or how a brake controller sending wire works? I'm guessing that modern (or even older) brake controllers have some sort of accelerometer in them to detect and calculate the braking force signal that should go to the trailer brakes. Am I correct in thinking the "brake sending" wire is nothing more than essentially an on/off signal? More questions appear: why couldn't you get that signal straight from the brake light wire, and/or if there's more to such a wire, then what application would it be used for if not for a brake controller and if the engineers saw fit to include a brake sending wire then why the heck didn't they just make it simple to add a full 7 pin outlet? Must I think of everything?!?! LOL

And as I said, I'm picking up my travel trailer tomorrow, they're wiring in a brake controller and 7 pin system. I'm paying them to do it because it's so ridiculously convoluted to simply add those functions to an already equipped "tow package" from Toyota. I was just trying to give the dude who's going to wire it a jump start (applying all the stuff that's spelled out in the "dozen" threads I've already researched). It's dark now, I guess he'll have to figure it out on his own! Oh, and @wngrog I'd like to see the guy who did yours for $50!!! This thing is gonna cost me $250 for the controller and another $250 to spend 4 hours wiring it!

To the dudes who answered the "what's this plug" question; THANKS!! It's useless, just as I had suspected! LOL

Eyedaho · Jul 14, 2020

HawkDriver said:
Thanks MJK!

Yep, those are among the "dozen" threads I read. Can you expand on what an AUX power does for the trailer, or how a brake controller sending wire works? I'm guessing that modern (or even older) brake controllers have some sort of accelerometer in them to detect and calculate the braking force signal that should go to the trailer brakes. Am I correct in thinking the "brake sending" wire is nothing more than essentially an on/off signal? More questions appear: why couldn't you get that signal straight from the brake light wire, and/or if there's more to such a wire, then what application would it be used for if not for a brake controller and if the engineers saw fit to include a brake sending wire then why the heck didn't they just make it simple to add a full 7 pin outlet? Must I think of everything?!?! LOL

And as I said, I'm picking up my travel trailer tomorrow, they're wiring in a brake controller and 7 pin system. I'm paying them to do it because it's so ridiculously convoluted to simply add those functions to an already equipped "tow package" from Toyota. I was just trying to give the dude who's going to wire it a jump start (applying all the stuff that's spelled out in the "dozen" threads I've already researched). It's dark now, I guess he'll have to figure it out on his own! Oh, and @wngrog I'd like to see the guy who did yours for $50!!! This thing is gonna cost me $250 for the controller and another $250 to spend 4 hours wiring it!

To the dudes who answered the "what's this plug" question; THANKS!! It's useless, just as I had suspected! LOL

The brake controller wire isn't just tied into the brake light signal because you don't want to have a digital on/off signal for brakes, unless you don't mind spilling your coffee and buying a lot of trailer tires. The brake controller itself uses a signal from the brake pedal/brake light. Most also use an accelerometer as you suspected, as well as internal logic and a user offset to determine how strongly to engage the trailer brakes. Too much engagement and your trailer isn't helping with the braking. Too much engagement and you're smoking your trailer tires and spilling your coffee down the front of your shirt.

The auxiliary 12V wire to the 7-pin is typically used to charge the breakaway battery on trailers that use one. That battery is what powers the trailer brakes if it comes disconnected from the towing vehicle and pulls out the activation pin, which is connected by a small cable to the tow vehicle. Some trailers also use that 12V wire for power for interior lights etc I think, depending on how they're set up.

MJK · Jul 14, 2020

A trailer brake controller is a two wire system that controls the brakes of the trailer electronically. The sending wire is positive, and uses a shared ground. Variable voltage causes variable braking force. It is not an on/off switch. The controller uses an accelerometer, but also has an adjustable gain setting to accommodate for varying weight and trailer brake conditions. There are also rare conditions under which you'd want to apply trailer brakes but not vehicle brakes. This allows all of the above to happen.

Aux power is just what it sounds like. It is a switched 12V charging system for battery powered things in the trailer. So, my dump trailer has a hydraulic ram powered by a car battery. It uses the Aux power to recharge that battery while you are driving. Your camper may or may not have such a system.

As for why 7 vs 4 - Older and lighter duty trailers are commonly 4 wire. More recent and heavier trailers are required by law to have electric brakes, and hence they need a mechanism to control them. Some also have reverse lights/cameras, etc. Converting from 7 back to 4 is an easy adapter you carry with you or accomplished via a 4+7 receptacle.

+ Adding the reverse wire is typically accomplished by tapping into the trucks reverse light bulbs. This may not be necessary for your trailer, if it does not have reverse lights or cameras.
+ Adding the 12V aux is again situational (EDIT: but see breakaway as noted above)
+ Adding the brake sending wire is important. Typically the controller is added to the cabin where it accessible by the driver. You provide it switched 12V+ and a ground, and it outputs the sending signal to the correct pin. This same function CAN be accomplished via your phone & a removable bluetooth controller at the plug if you are so inclined.

HTH and good luck.

gregnash · Jul 14, 2020

MJK said:
A trailer brake controller is a two wire system that controls the brakes of the trailer electronically. The sending wire is positive, and uses a shared ground. Variable voltage causes variable braking force. It is not an on/off switch. The controller uses an accelerometer, but also has an adjustable gain setting to accommodate for varying weight and trailer brake conditions. There are also rare conditions under which you'd want to apply trailer brakes but not vehicle brakes. This allows all of the above to happen.

Aux power is just what it sounds like. It is a switched 12V charging system for battery powered things in the trailer. So, my dump trailer has a hydraulic ram powered by a car battery. It uses the Aux power to recharge that battery while you are driving. Your camper may or may not have such a system.

As for why 7 vs 4 - Older and lighter duty trailers are commonly 4 wire. More recent and heavier trailers are required by law to have electric brakes, and hence they need a mechanism to control them. Some also have reverse lights/cameras, etc. Converting from 7 back to 4 is an easy adapter you carry with you or accomplished via a 4+7 receptacle.

+ Adding the reverse wire is typically accomplished by tapping into the trucks reverse light bulbs. This may not be necessary for your trailer, if it does not have reverse lights or cameras.
+ Adding the 12V aux is again situational (EDIT: but see breakaway as noted above)
+ Adding the brake sending wire is important. Typically the controller is added to the cabin where it accessible by the driver. You provide it switched 12V+ and a ground, and it outputs the sending signal to the correct pin. This same function CAN be accomplished via your phone & a removable bluetooth controller at the plug if you are so inclined.

HTH and good luck.

Very nice explanation @MJK