XJ electric trailer brakes

[eaglescout526]

I know its not MJ and Pete I can move it to the pub if necessary but I do want a lot of eyes and thoughts on this. So Chunk now has the trailer harness hooked up and wires are crimped into terminals to match the electric manual minus power from the power seats and mirrors wire, I see this little note and I am wondering and I have my doubts given how little XJs we are seeing these days but someone mustve seen something like this. It says the wire is coiled and taped to harness is a similar fashion like the cargo lamp wire on the MJ. Now I havent exactly dug around the electrical manual for this electric brakes but I am curious if anyone on here has seen or knows about such. 

 

[eaglescout526]

Ok I did a little more digging and read the diag portion of the manual and it says it is a module on the master cylinder(not the sentry fluid sensor). FYI the manual I am reading is for 1985, my 84 manual doesnt have a lot believe it or not, but it has the basics. I am gonna look in the parts manual. Now I am curious if anyone has seen such a module that wasnt the late ABS stuff.

[Pete M]

first I'm hearing of it.   

[eaglescout526]

Same goes for me. I found it in the electrical manual but nothing in the parts manual which has me confused

[Ωhm]

88 XJ Electrical

 

[eaglescout526]

On 10/29/2023 at 8:57 AM, Ωhm said:

88 XJ Electrical

 

I’ll have to look at my 88 parts manual and see if it’s in there. 
 

That being said, if anyone was to go this route, how would you set it up so the electric brakes would work on a trailer? 
I don’t plan to use or tow a trailer that uses a type 2 plug but it would be really nice to just have that as a worst case or a simple move 15 ft. 

[Ωhm]

1 hour ago, eaglescout526 said:

That being said, if anyone was to go this route, how would you set it up so the electric brakes would work on a trailer?

 

Trailer brake rheostat.

[gogmorgo]

Usually this would just be to simplify adding in an aftermarket brake controller. Often you’ll have a wire coiled up under the dash that runs to a similarly terminated wire somewhere under the rear panels. The idea is you pull power and ground from somewhere under the dash to power the controller, tap into the brake switch wiring as a trigger for it, and then this wire carries the output from the controller to the appropriate pin on the trailer connector.

 

You’ll see a coiled and taped wire like this even in much newer vehicles with enough towing capacity you might want to add a brake controller, like say a minivan, but where it’s not common enough that it’s worth it for the manufacturer to add a specific connector in every vehicle sold like most trucks from the 90’s on had until they started putting in brake controllers from the factory. I’m pretty sure the ZJ has a similar setup, although I’ve never investigated.

 

Brake controllers and trailer connectors are pretty cheap if you want to add one, although it’s not really something I’d want to install if I didn’t need to. Not a lot of place to put one in a small cab, they’re not usually very nice to look at, and they like to stick out and smash your knees, or they make doing other interior work obnoxious. Seems like they’re always mounted through a panel I need to remove when they could have been mounted a few inches over and never been a problem.

If you’re only moving 15 feet you likely aren’t going fast enough the vehicle’s brakes won’t hold up. You can also get brake controllers that go between the vehicle and trailer connectors so you don’t need to mess with vehicle wiring, so long as you have power to the 12V pin on your 7-pin connector. They’re good for towing with a borrowed vehicle or one you won’t be towing with often.  
 

You can also just shove 12V directly down the wire if you want to, although that will send full power to the trailer brakes, probably lock them up. The beauty of a brake controller is it varies the output voltage depending on how hard you’re decelerating, which varies the stopping power of the electric brakes and it’s typically adjustable to account for differences in trailer weight. I’m sure you could figure out how to replicate it on your own, but by the time you’ve sorted out a variable output for them you might as well have just bought a brake controller. 

If you are installing one, inertial is best. It accounts for how hard you step on the brakes. The time-delay controllers just slowly ramp up the output from when you hit the brakes, which isn’t as useful in an emergency braking scenario. Modern controllers have accelerometers in them, and can be mounted in any orientation, but the old analogue ones have a weight on a spring hooked up to a rheostat, and need to be mounted at a specific angle so the weight moves in the correct direction when you hit the brakes. It’s one of those cool analogue systems but I imagine they don’t work so good if the trailer shoves you sideways.