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Author Topic:   Trailer Lights
Maximus posted 04-19-2005 10:21 PM ET (US)   Profile for Maximus   Send Email to Maximus  
Well the fun with my EZ-Loader never ends...

My trailer lights don't work. I can hook up an external 12 volt power source with aligator clips and make them work. But when I hook up the truck's flat four they don't work. Also, a 'referee' truck worked with the trailer without issue. The problem has to be with the truck wiring.

Flat four basics...

White Wire: Ground
Next wire (#2): Rear lights and clearance lights
Next wire (#3): Left Brake
Next wire (#4): Right Brake (or vice-versa)

Here's what I have done to diagnose/fix the problem:

I checked the ground on the truck connector, no resistance between the white wire and a bolt on the truck bed, meaning I have a good ground. Volt meter shows 12 volts between the ground on the flat four and wires 2-4 on the flat four (when powered). My trailer light tester, a mating connector with 3 LED's that light up confirming power, confirmed my findings with the volt meter.

Thinking the truck's connector was a bit corroded, I snipped the end and spliced in a new end...$3 fix, right...wrong. Same thing, power and a good ground but when I hook it up to the trailer, no lights.

Next, I replaced the entire truck wiring harness...$35 fix, right...wrong. Same thing, power and a good ground, but no lights.

Frustration sets in...

I snipped the trailer's flat four. I spliced in a new connector...the other half of the $3 fix from above. Prior to sealing up the connections, I attached the new trailer flat four to the new truck flat four. The lights still don't work.

I checked for power at the splice location (12 volts between the white wire and wires 2-4 and I get nothing (when powered)). I unplugged the truck connector and checked power between the the white ground and the other wires and I have power.

Arrgh...what do I do next?

jimh posted 04-20-2005 08:38 AM ET (US)     Profile for jimh  Send Email to jimh     
The problem seems to be on the vehicle side of the connection, so perhaps it is more appropriate to mention the brand of vehicle than the brand of trailer.

About all I can suggest:

--perhaps when you measure the 12-volts available from the trailer it is a "ghost" feed. There is enough current available to make a meter read, but not enough to light a miniature electric light bulb. Test your vehicle connector with an actual load. The solution could be as simple as a blown fuse. The 12-volts you are seeing on the meter might be some circuit sensor voltage floating on the line.

davej14 posted 04-20-2005 08:48 AM ET (US)     Profile for davej14  Send Email to davej14     
This is definnitely a strange one. It seems like you have checked everything thoroughly. A couple of suggestions:

1. Have you tried your vehicle with another trailer to see what happens? It probably will not work but if this would be easy for you to try it would also confirm the problem with the vehicle.

2. You didn't mention the ground connection from the connector to the trailer. If the referee truck had a good connection via the hitch ball it would work even if the connector ground to the trailer was bad. Most often these are ground problems.

3. Was the vehicle factory wired or do you have an aftermarket installation? In an aftermarket job they often install a module with a separate power lead to handle the trailer load. Since the voltage at your connector is correct and the led's on your connector light up properly, then there must be an inadequate current path to the connector. If there is a module, check for corrosion where it is grounded to the vehicle and also inspect the power lead. If all looks well then I would replace the module next.

Maximus posted 04-20-2005 10:16 PM ET (US)     Profile for Maximus  Send Email to Maximus     
Sorry, I was frustrated last night.

Truck is a 93 Toyota Pickup. Wiring harness is an aftermarket type. It plugs between the exisiting connections at the two rear lights. As I said before, I replaced this already.

I don't have a second trailer to test things on as well.

I am going down the path of enough voltage, but not enough current. Any idea how to check this? Why would things change, everything worked great last season.

Also, the truck was not hitched to the trailer last evening during my trials, so no ground through the ball. I'll try this next.

HAPPYJIM posted 04-20-2005 10:44 PM ET (US)     Profile for HAPPYJIM  Send Email to HAPPYJIM     
Try using a test lamp to check the truck wiring. I have a digital multimeter that is almost useless for checking lighting circuits. The flashers on the truck run too fast for the meter to pick up a reading. I paid $100 for the meter at Radio Shack but a $5 test lamp with a needle probe is the best for checking 12 volt lighting circuits.
high sierra posted 04-20-2005 11:10 PM ET (US)     Profile for high sierra  Send Email to high sierra     
Bad ground. High Sierra
high sierra posted 04-20-2005 11:53 PM ET (US)     Profile for high sierra  Send Email to high sierra     
To elaborate a little, take a jumper cable and connect it to your truck at a clean spot and connect the other end to the trailer. Scrape off the area where you connect the cable. Connect your 4 way plug and the lights should work if the ground was the problem. This is only to check the grounding of the vehicles.
Jerry Townsend posted 04-21-2005 12:33 AM ET (US)     Profile for Jerry Townsend  Send Email to Jerry Townsend     
Maximus - since no lights work - the problem is something common to all lights. The only thing that is common to all lights is the ground - you say the connector ground is good to the vehicle ground - what about the trailer ground - from the trailer ground connector to each of the lights?

And I have misunderstood - but don't rely on a good ground through the hitch. ------ Jerry/Idaho

Maximus posted 04-21-2005 07:52 AM ET (US)     Profile for Maximus  Send Email to Maximus     
Game plan:

1. Hitch truck and trailer, try again.
2. Run a dedicated test line from battery ground to truck trailer wiring ground.

I'm using my trusty Simpson meter (analog display).

davej14 posted 04-22-2005 02:09 AM ET (US)     Profile for davej14  Send Email to davej14     

If the test line to the truck trailer ground doesn't work, be sure to run this line directly to the trailer frame and test that also.

I have a shorelander galvanized trailer and one of the lights didn't work. There was a separate ground lead from the trailer light assembly to the trailer frame and this connection was corroded. Cleaning it up solved the problem.

Let us know how you make out.

Knot at Work posted 04-22-2005 07:33 AM ET (US)     Profile for Knot at Work  Send Email to Knot at Work     
I recommend that you disconnect the lights before submerging the trailer in and out. I always disconnect the light and then reconnect after haul out. Cuts back on corrosion.

Just a thought.

Jerry Townsend posted 04-22-2005 10:27 PM ET (US)     Profile for Jerry Townsend  Send Email to Jerry Townsend     
To eliminate corrosion - simply clean your contacts and then give the bulb base a generous coat of vasoline - a silicone grease works too. - -- Jerry/Idaho
Chuck Tribolet posted 04-26-2005 05:12 PM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
Vaseline melts when it gets hot out. The right silicone
grease doesn't.


Buckda posted 04-26-2005 05:25 PM ET (US)     Profile for Buckda  Send Email to Buckda     
The fact that the trailer was not attached to your vehicle via the hitch may be the problem. I just rewired my trailer over the winter and added LED lights. When I first connected the lights without hooking up the hitch, I had nada - nothing! "How the H*** does that happen?!" I hook up the trailer to pull it out of the barn for some better light, and the lights flickered on.

Give that a try. Sometimes it's the simplest thing.

kingfish posted 04-26-2005 07:06 PM ET (US)     Profile for kingfish  Send Email to kingfish     

You must be grounding through the hitch from the trailer to the vehicle rather than with a separate ground wire, or your ground wire is faulty around the vehicle somewhere.


skred posted 04-27-2005 08:47 AM ET (US)     Profile for skred  Send Email to skred     
Kingfish has it right. You need a solid ground (white wire) connection to the trailer frame, and a solid ground connection on the vehicle side with the white wire from the vehicle connector. You're only grounding through the hitch metal-to-metal contact now.
Maximus posted 04-27-2005 09:12 AM ET (US)     Profile for Maximus  Send Email to Maximus     
I haven't posted a follow up because I haven't had time to try any of the suggestions yet. Stay tuned...
JohnJ80 posted 04-28-2005 04:01 PM ET (US)     Profile for JohnJ80  Send Email to JohnJ80     
Almost positive this is a bad ground. When grounds are bad, things get flaky.

The LED lights will be MUCH more sensitive to this than the incandescent. LEDs need to have a min voltage to light and are not as 'analog' as incandescent lights are.

The suggestion to take a wire right back to the battery terminal is the right one. Here is what I would do.

1. Get a 15-20' long wire. Connect it to the (-) terminal, directly on the batter.

2. Disconnect the ground wire from the vehicle flat connector. Splice this with a wire nut to the long wire connected to the battery.

3. Give it a try, my bet is that it works.

4. If that doesn't work, then run that long wire to the trailer after reconnecting the vehicle flat to the local connection. Try it again.

5. If this works, then the ground connection to the trailer is bad. Ohm out the connection from the end of the trailer flat to the trailer frame (scratch it to get down to metal). You may have to do this where ever each light attaches.

But, since another truck works, my bet is that the ground connection on the vehicle side is the problem.


Chuck Tribolet posted 04-28-2005 07:06 PM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
John's post gave me another thought: Check the battery
voltage. If it's low (< 12.5V), fire up the truck and
check again, it will probably go up to the high 13's. Now
do the light work? If so, it's the battery.


Maximus posted 04-28-2005 08:34 PM ET (US)     Profile for Maximus  Send Email to Maximus     

I tried starting the truck, thinking the battery was weak. No change. I'm pretty much convince of a truck ground problem as well, although zero resistance between the white truck wire and metal on the bed suggests not.

I am anxious to got try anything at this moment. Rain and other crisis have kept me from continued troubleshooting.

Chuck Tribolet posted 04-28-2005 11:44 PM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
Maybe the bed's insulated from the frame? That's not
impossible -- lotsa stuff gets rubber mounted these

What kind of truck?


Chuck Tribolet posted 04-28-2005 11:46 PM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
Never mind about the type of truck, you already said '93


Mako posted 04-29-2005 11:54 AM ET (US)     Profile for Mako  Send Email to Mako     
Back when I had my truck ('93 Toyota 22RE), I had problems blowing the speedometer fuse everytime I reversed with the trailer attached. Turns out the problem was the brake disable which connects to the reverse light wasn't grounded or something. Anyway, cutting the reverse wire at the harness fixed the problem. I don't have trailer brakes anyway.

Here's what I'm thinking: The wiring for the Toyota must be different on every car, or you have a Reese harness like I did and they're doing something wrong. Figure out which wires perform which function on the flat-four, then make sure they're attached to the appropriate wires on your truck's electrical. Don't just trust the wiring harness. Hope that helps.

Maximus posted 04-30-2005 12:22 AM ET (US)     Profile for Maximus  Send Email to Maximus     
I hitched the trailer to the truck this evening and initially got some flaky results, but all seems well now.

At this point, I had the new wiring harness in the truck, a new flat for connector on the trailer and some quick connects between the new trailer flat four and the trailer wiring harness.

Frustrated with the continued failure of the lights, I asked my wife to review the connections. Being color blind, I had inadvertantly confusted the green and brown wires! The trailer actually has five wires: yellow, white, green, brown, and green (again). The green's get paired.

With the connections corrected and the trailer hitched to the truck, everything seems to be working correctly.

In summary,

1. it appears that both the flat four connectors (trailer and truck) may have need to have been replaced due to corrosion and poor conductivity.

2. The truck wiring harness (aftermarket) probably didn't need to be replaced, but no harm done.

3. The trailer needs to be hitched to the truck to get a good ground, as the single white wire seems to be a marginal ground.

4. I had mixed up the green and brown wires during some of my eariler troubleshooting attempts, doh!

All connections have been mended with solder, shrink wrap tubing, and tape.

Come hell or high water, the boat gets launched this weekend.

Thanks for all of your help.

JohnJ80 posted 05-01-2005 07:08 PM ET (US)     Profile for JohnJ80  Send Email to JohnJ80     
LOL - I had a friend who was color blind and an electrical engineer. When we worked in the lab together, he was a real pain since we couldn't make out the wire colors or the resistor sizes (colored strips). Made for some spectacular shorts!

On the ground - if it only works when the trailer is on the ball, then you have a bad connection for the ground on one side or the other. I would spend some (more) time following those to where the make contact and making sure that they are done properly. If the best ground is coming through the ball, then you are going to have flakiness in the future. The wire grounds should be MORE than enough to handle any current the trailer needs.


Barney posted 05-01-2005 07:56 PM ET (US)     Profile for Barney  Send Email to Barney     
Max, I know what your problem is. Road salt. You need to move south. Jim

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