Trailer lights wiring

[Knucklehead97]

I'm looking at buying a 6×12 single axle trailer from a guy for a really good price. But my Jeeps trailer wiring was done terribly and I'm sure it doesn't work. How do I splice this all in? It's just a 4 prong flat connector. Also... my reverse lights don't work at all, anybody know a possibility of why?

[HOrnbrod]

With a 4-pin flat connector you don't wire in the brake lights on an MJ since the brake lights and turn signal lights each have their own bulbs. But that's okay in AL; that's what I have for my trailer. If you want the brake lights too you'll need to use a 5-pin flat connector.

 

No backup lights is probably the NSS.

[ParadiseMJ]

Being a rank beginner in the wiring department when I did mine, I got excellent results using a voltmeter with bared wires and a friend to work the signals, brakes, running lights, when I found the corresponding wire (from the truck) I confirmed on the trailer lights plugged in with the wires twisted together. Follow the directions on the wiring kit as to colors.  Then take each set apart and solder them securely. Slide the shrink wrap on each wire beforehand and keep it well back from the soldering heat. When you're done, slide the heat shrink over the cooled wires and shrink 'em. Then put them all together and stuff them into wiring loom and tape it up. 

 

Should last forever. Make sure the white wire (on the trailer) is grounded, and a good ground on the truck too!

 

With the flat 4 (truck side) you'll get about 4 feet of wire.  Abbreviate to about 2

 

Look for the 7.5 A "TRANS" fuse under the dash, before you mess with the NSS.  If that doesn't work search for NSS cleaning write-ups (numerous).

 

I wired the brakes up on both my Jeeps...may not need to in AL, need to in CA.  Just sayin' it's a safety thing for me.  I did not wire in back-ups, I only have a 5'x8' utility trailer and a small boat trailer.

[johnj92131]

My truck had some old trailer wiring that simply did not work - I took the easy way out and paid a local shop $90 to install a new, clean 4 pin connector. 

 

All I did was go have breakfast at a near by cafe, then go back an hour later and pick up the truck.  The new harness works great, first time, every time.

[Blue88Comanche]

Mine is currently spliced into the brake lights.  I used a multi-connector plug that will accept 7, 5, and 4 pin.  I plan to wire in Reverse lights and trailer brakes, i may never use them but i like having the option. 

 

New Trailer harness plug by Blue88Comanche, on Flickr

[fiatslug87]

My reverse lights occasionally will not work but if I mess around with the NSS connector at the harness (near firewall on passenger side) they will. I have not tracked down if the problem is the NSS connector or the harness connector since I rarely use reverse in that truck.

 

And happy 1000th post!

[Ωhm]

Turn signals lights (L or R) and brake lights (L and R) are basically the same circuit. If you hookup L/R turn signals, you'll get brake lights. Brake lights use the same filament as does the turn signals. Circuit is either a brake circuit or turn signal circuit.

[HOrnbrod]

Turn signals lights (L or R) and brake lights (L and R) are basically the same circuit. If you hookup L/R turn signals, you'll get brake lights. Brake lights use the same filament as does the turn signals. Circuit is either a brake circuit or turn signal circuit.

 

True for an MJ, but not for an XJ. XJ's have separate turn signal bulbs. I always mix up the two...........

[ParadiseMJ]

Don't XJ's have an adaptor that manages the circuits.? I think it's a blue wire for the trailer brakes and a tan/black wire for the back-ups. 

 

My XJ has a 6 prong connector with a 4 flat adaptor at the bumper that leaves out the trailer brakes and back-ups, unless trailer has the 6 prong one too.

[Knucklehead97]

I now regret not buying one of the 5$ NSS's when Rockauto had them mis-priced. But at least you can clean NSS's! I doubt I will ever tow a trailer big enough to have trailer brakes so I think that a 4 prong connector will be good. 6×12 is going to be the biggest this Jeep will haul most likely. Definitely will be upgrading the MC/booster and deleting the rear sensing valve eventually since I will be towing some. I've just got to find time to mess with the trailer wiring... if I get the trailer. Going Saturday if he hasn't already sold it.

[HOrnbrod]

Don't XJ's have an adaptor that manages the circuits.? I think it's a blue wire for the trailer brakes and a tan/black wire for the back-ups. 

 

My XJ has a 6 prong connector with a 4 flat adaptor at the bumper that leaves out the trailer brakes and back-ups, unless trailer has the 6 prong one too.

 

I believe it's called a logic module. I had to use one when I installed a third brake light on my camper shell. It was either that or run a new trigger wire from a set of the NO contacts on the brake pedal switch.

[Ωhm]

Looking at the wiring diagrams for MJ and XJ, both have the same Turn Signal switch. Should be the same on both vehicles. Yes NSS is for back up lamps only.

[Eagle]

 

Don't XJ's have an adaptor that manages the circuits.? I think it's a blue wire for the trailer brakes and a tan/black wire for the back-ups. 

 

My XJ has a 6 prong connector with a 4 flat adaptor at the bumper that leaves out the trailer brakes and back-ups, unless trailer has the 6 prong one too.

 

I believe it's called a logic module. I had to use one when I installed a third brake light on my camper shell. It was either that or run a new trigger wire from a set of the NO contacts on the brake pedal switch.

 

 

A logic module is used when adapting a vehicle with separate turns (like an XJ) to work with a trailer that has a flat, 4-pin connector. What does it do on your MJ's camper shell?

[HOrnbrod]

Logic module is a generic term and they are used for many different applications. This particular logic module is for third brake light installations and allowed me to pick up the brake switch 12V signal for the third brake light at the tail lamp harness w/o interference (flashing) from the turn signals. How it does this internally I don't know, but w/o it if I used the turn signals while braking the third brake light would intermittently flash in time with the turn signals.

[HOrnbrod]

Don't XJ's have an adaptor that manages the circuits.? I think it's a blue wire for the trailer brakes and a tan/black wire for the back-ups. 

 

My XJ has a 6 prong connector with a 4 flat adaptor at the bumper that leaves out the trailer brakes and back-ups, unless trailer has the 6 prong one too.

 

Does your XJ have the Trailer Tow option?

[mikekaz1]

With a 4-pin flat connector you don't wire in the brake lights on an MJ since the brake lights and turn signal lights each have their own bulbs. But that's okay in AL; that's what I have for my trailer. If you want the brake lights too you'll need to use a 5-pin flat connector.

 

No backup lights is probably the NSS.

 

hmm, sorry but this doesn't sound correct....    MJs most certainly can use a 4 pin standard harness. and a 5 pin is historically used for reverse trigger.

[Knucklehead97]

Being a rank beginner in the wiring department when I did mine, I got excellent results using a voltmeter with bared wires and a friend to work the signals, brakes, running lights, when I found the corresponding wire (from the truck) I confirmed on the trailer lights plugged in with the wires twisted together. Follow the directions on the wiring kit as to colors. Then take each set apart and solder them securely. Slide the shrink wrap on each wire beforehand and keep it well back from the soldering heat. When you're done, slide the heat shrink over the cooled wires and shrink 'em. Then put them all together and stuff them into wiring loom and tape it up.

 

Should last forever. Make sure the white wire (on the trailer) is grounded, and a good ground on the truck too!

 

With the flat 4 (truck side) you'll get about 4 feet of wire. Abbreviate to about 2

 

Look for the 7.5 A "TRANS" fuse under the dash, before you mess with the NSS. If that doesn't work search for NSS cleaning write-ups (numerous).

 

I wired the brakes up on both my Jeeps...may not need to in AL, need to in CA. Just sayin' it's a safety thing for me. I did not wire in back-ups, I only have a 5'x8' utility trailer and a small boat trailer.

I changed the fuse and my passenger reverse light works! Thanks! The other ones bulb is blown, easy enough fix. Ends up there were quite a few blown fuses on this Jeep.