I have recently replaced the wiring in my utility trailer and mechanic has tested lights when in the shop and says they're all working fine. Hooked it up to my pathfinder and lights were not working. He tested the wiring going into the 5 amp tail light converter and all wires going into this had power, however, one of the wires coming out of the converter did not have power. I bought I new converter and wired it in just like the old one was wired in. Now lights on trailer only come on when the vehicle lights are turned on and sometimes even then the driver's side trailer brake and turn lights do not work. Any suggestions? New to all this but all my wires seem to be connected fine...I just don't have a tester thing of my own and don't want to pay again for a mechanic as it seems it should be very staightforward.....Thanks in advance for your help!

There are several potential reasons why the trailer lights on a 1998 Mitsubishi Montero might not be working:

1. Blown Fuse: Check the fuse panel for a blown fuse related to the trailer lights. Replace the fuse if it is blown.
2. Wiring issue: Inspect the trailer light wiring for any signs of damage or corrosion. If there is damage, repair or replace the wiring.
3. Bad Ground: Make sure that the trailer lights have a good ground connection. Test the ground connection to ensure it's making a good electrical connection.
4. Faulty Light Bulbs: Check the trailer light bulbs to see if they are burned out. Replace any damaged or burned-out bulbs.
5. Trailer Light Connector: The problem could be with the trailer light connector. Check the connector for any signs of damage or corrosion. Clean the connector or replace it if needed.

If you are unable to resolve the issue, it may be necessary to take your vehicle to a qualified mechanic for further inspection and repair.

Some people wire trailer plugs differently. If the plug is not wired differently than yours, make sure the tow ball is clean. No rust. That's where the trailer gets its ground from. Usually they will work if thats the case, but not right. I can't remember what the wire colors are right now. Go to etrailer and look up the diagram.

check to see if the ground wire is making good bare metal contact on the trailer.

Thanks Syntax Error for letting us know you figured out the wiring harness was wired incorrectly. It is always a good idea to look up the color wiring standard for the socket and to check the pin positions and what functions .
Sometimes trailers can be wired incorrectly also ?
I wired the licence plate bulb to my brown wire by mistake and this is the brake wire . Took a while for me to figure that one out !

You shouldn't need the license plate lights to work to make your trailer lights work. Chances are that there is an issue with the wiring it's self. On my father 94 pick up the wiring is spliced directly in the taillight wiring. If your taillights work there shouldn't be an issue with the trailer lights. Start by checking or remounting the ground wire attached to the wiring harness. If that isn't the issue test the input of the harness followed by the output. If there is input but no output you need to replace the harness. Try the CURT 55379 you can purchase this by visiting one of their retailers by clicking here.

Your trailer connector is wired wrong or shorted. Check the connections at the car.

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Trailer Wiring Diagrams 4 Way Systems

4 way flat molded connectors allow basic hookup for three lighting functions; right turn signal / stop light (green), left turn signal / stop light (yellow), taillight / license / side marker (brown) and a ground (white).

4 way tow vehicle side.
4 way trailer side.
5 Way Systems

Same as 4 way system listed above but adds a extra blue wire for brake signal or auxiliary power. Used on pop up camper trailers or utility / boat trailers.
5 way tow vehicle side.
5 way trailer side.
6 Way System, Rectangle Plug 3/4 inch by 1 inch 6 way rectangle connectors right turn signal (green), left turn signal (yellow), taillight (brown), ground (white). The red and blue wire can be used for brake control or auxiliary. Use on a small motorcycle trailer, snowmobile trailer or utility trailer. Can also be used as custom wiring on trailers with 3 light/wire systems. See "Tow Vehicle Taillight Wiring" below.
6 way tow vehicle side.
6 way trailer side.
6 Way Systems, Round Plug

Round 1 1/4" diameter metal connector allows 1 or 2 additional wiring and lighting functions such as back up lights, auxiliary 12v power or electric brakes. Note: The black (sometimes red) 12v and blue electric brakes wire may need to be reversed to suit the trailer. Check with a test light or VOM. Uses: horse trailer, travel trailers, landscaping trailer, car trailer, etc.

6 way tow vehicle side.
6 way trailer side.
7 Way Systems

Round 2" diameter connector allows additional pin for auxiliary 12 volt power or backup lights. Uses: heavy duty landscaping trailer, car trailer, boat trailers, horse trailer, travel trailer, construction trailer, etc. Check with a test light or VOM.

7 way RV flat blade tow vehicle side.
7 way RV flat blade trailer side.

is the trailer attached to the ball on the van?? could be a ground problem,,run a jumper from hitch to trailer see if that works,,

most trailers don't have fuses, but rely on the car fuses, and if the car lights go on, that can't be it.
You need a test light.
Check if the current is getting to the trailer connection, then check at the trailer bulbs.
But the ground connection is the most likely if none work.
The trailer itself is the ground for the lights, but you need a brown wire from the trailer frame to car frame/ground.