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Author Topic:   Trailer Lighting, More Questions
bigjohn1 posted 12-19-2005 07:58 AM ET (US)   Profile for bigjohn1   Send Email to bigjohn1  
Me and trailer lights, I guess they just don't mix. I am temporarily using the el-cheapo lights you bungie to your boat's rear cleats. This is a temporary thing till I get some real lights after Christmas. I have a Toyota dealer-installed class-III hitch and a flat style 5-way electrical connector under my truck's bumper. The LED lights I had on my EZ Loader trailer hooked up to the truck via a common flat 5-way plug. Now these el-cheapo lights I am temporarily using have a flat 4-way plug (4 wires going into the plug vice 5). The stop, brake, and turn signal functions all work fine on these lights but NOT the running light function..its like the running light
bulb filament wire is burned out or something. I checked the bulbs and they look fine (they should be, they are the brand new bulbs which came installed in the lights).

Why can't my running lights work but all other functions work fine on these temporary trailer lights? Is it the 4-way plug (from the new temporary lights) going into my 5-way connector at the truck? They mate up and plug in just fine. Should I cut off my old 5-way connector from the old trailer lights and install it on the new set of temporary lights? How do these cleat-mounted lights get a ground since they are in no way electrically connected the the metal of my trailer? I HATE TRAILER LIGHTS.

Marlin posted 12-19-2005 08:18 AM ET (US)     Profile for Marlin  Send Email to Marlin     
John, it's not that you're using a 4-pin plug. The 4-pins are completely compatible with the 5-pins; the extra 5th one generally carries the backup lights, and is used to disable surge brakes.

I'd guess that you either have a bad plug or a broken wire on the trailer wiring, or less likely, that a problem has occurred with your truck wiring on that pin. If I remember correctly, the wiring sequence (in order on the plug) is:

|0| brown - marker/tail lights
|0| green - right directional/stop light
|0| yellow - left directional/stop light
|X| white - ground

Use a voltmeter (or one of those little plug-in testers) to check your truck's connector for 12V between the ground pin and the brown wire pin (at the opposite end of the plug). Of course, make sure the truck's parking lights are on. If that works, the problem is in the trailer wiring, and it might be worth trying to cut off the existing connecter and solder another one on. You might also check to see if there are any wire nuts or connectors elsewhere in the trailer wiring that may be bad.

I don't have any experience with trailer lighting that's not part of the trailer itself, but I'd assume that this add-on set must pull an additional wire for ground right to the lights.

Good luck.


Chuck Tribolet posted 12-19-2005 09:16 AM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
|0| green - right directional/stop light
|0| yellow - left directional/stop light
|0| brown - marker/tail lights
|X| white - ground

Other than that, Marlin's advice is good.

In my experience, it's most likely to be a problem at the
plug, either plug to plug, or the wire broken internally at
the plug.


bsmotril posted 12-20-2005 03:41 PM ET (US)     Profile for bsmotril  Send Email to bsmotril     
Euro style tailights as found in your Toyotoa have separate bulbs for turnsignal, and a second single dual filament for stop/run lights. American lights, and std trailer wiring uses a dual filamant bulb for running, stop, and turn signals. Toyotas, Nissans, and others need to add an adapter to the lighting circuit to function properly with a single dual filament bulb versus the two separate bulbs in their lighting circuit. UHaul sells them, probably plenty of other sources too. BillS
cmarques posted 12-20-2005 06:05 PM ET (US)     Profile for cmarques  Send Email to cmarques     
A couple years ago we hooked up trailer lights on my dad's 2002 Tacoma double cab. After fighting with a universal converter and trying to tap into the light circuits, we gave up and got a direct plug in 4 wire converter that works right. Like Bill said you can get them anywhere. Walmart carries them for less than $30 bucks and plug inline except for the ground wire.


Chuck Tribolet posted 12-20-2005 08:11 PM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
I agree about using the plug-and-play stuff on the truck


whalerwanter posted 12-21-2005 01:36 AM ET (US)     Profile for whalerwanter    
Recently, I rewired my trailer with a new LED kit. I had the same outcome: no running lights. My problem was a blown fuse in my truck. The fuse is located under the hood, not on the interior fuse panel. I never knew that box was there, until I read my owner's manual. I replaced the corresponding fuse, "tow running lights", and everything works fine. I have a Ford truck. You've probably wired everything correctly. Good luck.
davej14 posted 12-21-2005 10:44 AM ET (US)     Profile for davej14  Send Email to davej14     
Your brake lights and turn signals use either a separate bulb (or a different filament in a dual filament bulb) than the running lights. Since your brake lights and turn signals work fine you do not have a grounding problem. Simply trace the brown wire voltage to determine where the connection is broken. Checking the fuse first is a good idea if there is no voltage at the vehicle connector.

Good luck.

bigjohn1 posted 12-21-2005 05:29 PM ET (US)     Profile for bigjohn1  Send Email to bigjohn1     
Thanks for the help on this....there is no voltage at the vehicle connector so looks like I may have a blown fuse in the truck. I'll check that out and post a follow-up later today.
cmarques posted 12-21-2005 06:51 PM ET (US)     Profile for cmarques  Send Email to cmarques     
Whalerwanter- you are right about the Ford being fused seperate under the hood, don't know about other makes. I work at a Ford dealer and get several calls a week asking about trailer lights going out and truck lights still working.


Chuck Tribolet posted 12-21-2005 08:29 PM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
That separate fuse for the trailer is a good idea. There are
a lot of crummy trailer wiring jobs around. On my first
Pathfinder, I rented a car trailer to tow the FireTurkey
(1968 Firebird 400 Convertible) to the body shop for a paint
job. The engine was out being rebuilt. Anyway, we had a
lot of trouble getting the trailer lights to work, and it
turned out there was a short to ground. We kept popping the
primary tail light fuse. At least with a separate fuse,
you still have lights on the truck.


davej14 posted 12-22-2005 11:15 AM ET (US)     Profile for davej14  Send Email to davej14     

If you find the fuse is blown, replace it and before connecting to the trailer, check to see that there is voltage at the connector. If not check to see if the new fuse is blown. If so there is a problem in the vehicle harness.

If after plugging things together all works fine you are all set, but keep an eye on it. It is possible that there is a frayed wire within the trailer frame that may only contact the frame when in motion.

Good luck.

rtk posted 12-22-2005 11:59 AM ET (US)     Profile for rtk  Send Email to rtk     
Just went through this with a friend's trailer lights. First visit to his Ford dealer, blown fuses. Sent him on his way. I put a test light on it, reverse light pin no voltage. (7 way plug on vehicle)

He went back to the dealer, told them does not work.

They did discover a problem in the vehicle trailer lights wiring harness going to the plug.

I tested it at the plug, then disconnected the plug from the vehicle harness and tested directly at the vehicle wiring harness to eliminate a problem with the plug.

I was suprised to see a seperate factory wiring harness there dedicated for trailer lights and accessories. Alot of installations I have done "T"s into the rear harness for the vehicle lights. Seperate fuses for trailer lights and vehicle lights is a good thing. If the trailer is shorting out the trailer light supply it will not effect the vehicle running lights.


Jerry Townsend posted 12-22-2005 03:28 PM ET (US)     Profile for Jerry Townsend  Send Email to Jerry Townsend     
The seperate/multiple fuses arrangement can be done in two different ways 1) running the trailer lights from under the hood, or 2) pigtailing the trailer lights from the vehicle lights.

Now, if one is pigtailing the trailer lights from the vehicle lights - make sure the fuses for the trailer lights are rated for a lower/lessor amperage than the fuses located in the fuse panel/block. If the fuses are the same rating, the fuse for the vehicle will blow first - not what you want. ----- Jerry/Idaho

bigjohn1 posted 12-26-2005 07:09 AM ET (US)     Profile for bigjohn1  Send Email to bigjohn1     
OK, I finally found the culprit - it was a blown 5 amp fuse in the separate harness dedicated to the trailer lights. I did not realize Toyota Tacoma's came with a separate harness and fuse block just for the trailer lights/harness (this is separate from the under dash (#1) and under hood (#2). On a 2004 Tacoma Pre-Runner, it located underneath the driver's side rear jump seat next to the factory tire jack. As to the cause of my blown fuse, I looked the trailer over very closely and there was a frayed wire going to one of the lights and it was contacting the trailer fame. All is well now...thanks for helping me sort through this.
Tyouth posted 01-30-2006 09:59 PM ET (US)     Profile for Tyouth  Send Email to Tyouth     
Would one expect 12V from the working turn signals connections?

I have running lights but not turn signals on the trailer -truck is fine. I'm getting 4V at turn signal connections and no trailer lights. I assumed that the adaptar in my 2000 pre-Tacoma was the problem but when I wired up the new adapter got the same results.

Any thoughts? Have checked trailer wiring. All I can think of is to undo it and check it again.


jimh posted 01-31-2006 12:33 AM ET (US)     Profile for jimh  Send Email to jimh     
Try disconnecting the trailer from the vehicle. Then measure the voltage from the vehicle on its connector without the trailer attached. If you still only get 4-volts the problem is in the vehicle. If you get 12-volts the problem could be in the trailer or still in the vehicle.

Check the grounds. Many problems in trailer lighting circuits are caused if there is a bad ground. You can get sneak paths for current, and sometimes a lamp filament will conduct current without illuminating.

Tyouth posted 01-31-2006 06:51 PM ET (US)     Profile for Tyouth  Send Email to Tyouth     
Thanks for the reply Jim.

I didn't make it clear but the 4 v (alternating 4v, 0v)for the turn signal is at the trailer/vehicle harness connection.

jimh posted 01-31-2006 09:26 PM ET (US)     Profile for jimh  Send Email to jimh     
Measure the turn signal voltage under steady state. Have someone hold the turn signal stalk until it makes the lamps illuminate. Then measure the voltage. You may be seeing "4-volts" on your meter because of the on-off nature of the signal.

Also, are you sure the turn signal lamps in the car are designed for 12-volts? Newer cars have some fancy illumination and lighting system. To really test, temporarily wire a bulb across that circuit at the connector and see if the car can illuminate it. If not, problem definitely in the car. Or maybe a matter of the design--could it be some crazy LED lighting circuit?

Also, if you car in equipped with Euro-style tail lights, where there is a separate lamp for turn signal and a separate lamp for brake light, then you will need a convertor to reduce this to the standard 4-wire trailer system.

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