trailer wiring issue

Having a bit of an issue with the trailer wiring harness on my '98 xj.

I installed a Hopkins plug in wiring harness flat 4. plugged in a test plug, and plugged in boat trailer both giving the same issue. left/right, hazard, and stop work until i turn on running lights, then only running lights work, no brake or turn. The odd thing is if i probe the wires going into the back of the plug i get brake/turn with or without running lights. I have taken off every ground connector i can find sanded to bare metal and reattached. I even ran an extra ground from the ground wire between the plug and converter box to an existing ground bolt.
Taillights on the jeep itself work without issue. factory taillights with incandescent bulds. trailer lights, test plug, and test light are led. Continuity tester used to verify grounds.

Any help is appreciated, I've spent the better part of two days searching and testing solutions to no avail.

Rob277 said:

....Taillights on the jeep itself work without issue.

Click to expand...

I would consider that the Hopkins harness is defective.

Tim_MN said:

I would consider that the Hopkins harness is defective.

Click to expand...

^ .:gag:

That is a possibility, but it had a universal converter in it before that had similar issues. It was wired in with quick connects which were removed and wires repaired. Plus this seems unlikely considering if I probe the wires directly behind the trailer plug everything seems to work, but using a tester less than 2 inches away on the plug itself I run into problems.

Rob277 said:

..it had a universal converter in it before that had similar issues..

Click to expand...

Then I would suspect a wiring issue, probably some sort of probelm with ground, a short circuit/open circuit, or a defective bulb socket. You will need to inspect/test all the front and rear lamp circuits and bulb sockets. Also check the tailgate wire harness for short/open and failed wire splices.

Try a different trailer. There could be a short on the trailer side.

--Andy

Note from DJ
My ’88 has the factory towing harness wiring set up. It has the 7 blade RV connector that is connected to relays that are located behind the spare tire. They can be located by removing the spare tire & then remove the plastic cover in front of the body cavity back there.

This is all I have and my boat lights all work as they should, with no need for the 4 light to the 2 light conversion system. The relays do it for you.
NAPA Part Number: BK 7551560
Adapts 7 Blade RV Socket Into 4-Wire Flat On Trailer Side
http://www.napaonline.com/Catalog/CatalogItemDetail.aspx?R=BK_7551560_0006462383

Not all XJs came with the Tow package option, so you need to install an adapter between the factory wiring an the Trailer to convert from European lights to the old US system.

Let's see now...

The XJ lights work.
Both the tester and the trailer act the same.

Is the ground on the adapter (some have grounds) attached to a good ground?
Is the adapter in the right wire set?

my jeep is oddly optioned as it was originally a lhd postal jeep. I'm assuming it never had the towing package. When I got it there was no hitch receiver, or relays, it just had the universal converter and plug. The tester I'm using is the one that autozone sells made by Hopkins. It has four pins and uses the ground pin just like a trailer does. I have tested with probe clipping the ground to the ground pin as well as grounding straight to body.

I have tried two different boat trailers with the same results. Ground at plug tests good with continuity tester. Extra ground leads added before and after converter to rule out ground issue.

What's the part number of the adapter you are using?

Ok Rob there is an issue that is being overlooked here and let me share from one of my other towing trucks.

Truck I have is a '72 1210 International Pickup with a flat bed replacement for the factory bed. I wanted to convert the truck's rear taillights to LED. I went and bought the 4.5 or 5.5" round snap in style like big rig trailers and taillights use. My trailer is a homemade unit, that I rewired the entire harness and lights. Those lights are standard incandescent/halogen. My problem was when the trailer is connected same thing as you, with the parking lights on, the turns fail to work. Brake lights worked, but were real faint. I have found when you introduce a set of LED's to the factory wiring, the relay/flasher that works the turns gets tricked to think that the lights are "out", all lights, meaning that it doesn't have the necessary volts or amps to activate the relay/flasher unit. Two things helped my setup.

1. Redo the trailer ground wire for the trailer side. I used a flat electric meter box clamp, that uses 2 set screws to hold it on, and the third for the ground wire. This helped with the dim lights. Also check all the grounds for the tail lights on both the XJ and the trailer. The trailer lights ground to the trailer, which is grounded in turn to the XJ, via the trailer ball. So make sure that the tongue on the trailer and the ball are both super clean of oil, and rust. You need good metal to metal contact here. I also redid the wiring on the truck to have a ground for each individual light, which also helped. Grounds all need to be clean and clear. You indicated you checked all of these, but you might be missing one, so check them just to be sure.

2. Heavy duty flasher/relay installation. When you add more lights to the factory lights, it adds extra load/draw, and resistance to the system. Since the grounds are crucial to the whole deal working right, then this is the next option. On the aforementioned International truck, when I step on the brakes with the hazards on, they come on steady. This is because they use the same part of the light filament for the bulb intensity. In the case of the XJ, it uses a separate system for both the turns and the brakelights. In this instance, you have to have a converter unit to activate the turns on the trailer. These are sold as an all in one, or inline kit that goes into the factory connector behind the spare tire panel. Here there is a connector that separates into the DS and PS of the rear lights. There shouldn't be any of this in your hatch, as this wireset runs down the DS, then along the shelf part for the rear seat, where it then goes through a grommet on the floor. This might have changed for the later XJ's, but my '94 was set up this way, and I will have to check it my '00. Pull that panel and check and see if that connector on the kit, on each side has correct connection, and is clean. I had to replace this convertor unit on my first '94 as it went bad.

Try these suggestions and report back your findings on this, as I think you probably either have a bad ground, or the unit you installed is bad.

Jeff