braverex

I got a new trailer and the wiring seems to be giving me a little trouble. When I don't have the headlights on everything seems to work fine(brake,left,right) on the trailer. When I turn the headlights on none of the lights on the trailer work. I have a standard 4 prong trailer connector (3 male and one female). I was thinking my brown wire might not be connected to the wrong wire in my truck but any thoughts on what might be causing the problem?

Thanks!

Mark in MD

Hi. I've been pulling a trailer with a Toyota truck for 13 years.

You didn't mention whether you have an OEM wiring harness for your 4Runner, or if the wiring is the standardized colors which should match the trailer.

I'd crawl underneath and make sure the colors match leaving your 4runner and entering the trailer plug. You're right, the brown wire carries the current for the lights. The brown wire should be the one right next to the ground white wire.

Make sure the white wire is grounded to the trailer. Should be attached to a bolt next to the trailer tongue.

I'd get a multimeter and test the three connections coming out of the 4runner plug for current.

If there's no current in the one next to the ground (which is the brown wire), it might be because of corrosion in the pre-harness connection, which should be found about a foot or so above the plug, if you have a pre-harness connection.

Otherwise, the brown wire might be grounding out somewhere. I'd check the area where the harness enters the cab, which should be below the drivers seat.

Hope this helps.

braverex

It is an aftermarket install (i think UHaul). The wires seem to match up fine and I am getting a good voltage read when I have my headlights off. When I turn my headlights on though I don't get anything to work with the trailer lights. (all the lights on my 4Runner work like normal).

firemaniac

Have you tried hooking the trailer to a different truck to see if it is your truck or your trailer giving you the problem? if the problem is on the truck side I would first check/replace the ground from the connector, next the converter that combines the turn signal feed and the brake light feed into one wire (these have been known to go bad), also the wire spliced in for the tail lights (brown) on the truck side for a bad connection of coarse this assumes that badhaul used a hard wire kit instead of a T-plug kit (connects in line with the stock harness)

if it is on the trailer side I would check/repair the ground near the toung, after that check the lights grounds to the frame and then for shorts in the housing (eg. tail shorting to stop/turn) and make sure the bulb holders are clean and free of corrosion (could cause another short).

Either way check the grounds first on both the truck and trailer side.

Chris

nieuwendyk-25

Check the bulbs too they can sometimes cause funky problems it one of the elements is burned out and the others work.

firemaniac

Good point, bulbs are realitivly cheap.

Chris

braverex

Yeah, the bulbs are brand new and I just rewired the whole trailer side so I am confident in the grounding with that. I will check the grounding on the truck side to see if I can come up with anything.