Trailer electrical troubleshooting
#1
07-21-19, 09:50 AM
Trailer electrical troubleshooting
Due to the way and places I bring my trailer (open bed) (off road areas) I'm constantly breaking my tail lights. Since I want to be in compliance with the law while on the road, tracing breaks in the line is getting to be a pain. The big problem is having to attach the car or towing vehicle to the trailer in an effort to test and troubleshoot problems. Is there a way, using an outside 12 v power supply that I can use to test tail lights, brake lights, hazard lights and turn signal lights without attaching the towing vehicle? All the trailer lights are LEDs and integral with each type of light. In other words each LED cluster will be, turn signal, tail light, hazard light and stop light all in one.
Top Answer
07-21-19, 10:51 AM
Group Moderator
A trailer with a 4 pin connector really only has 3 functions: Running lights (brown), which the taillights are in lower output mode and the side marker lights if present, and left (yellow) and right (green) full bright on. The tow vehicle only does the controlling of the tail lights whether to be constant on when breaking, or flashing when signaling, but the light is the same brightness. Of course, the running lights are also from the tow vehicle but they are just a single on-off switch.
That said, yes, you can do all your testing with a 12-volt battery or 12-volt DC power source like a battery charger. If you connect the negative to the white pin, the positive will then be connected to any of the other pins (green, brown, yellow) to test. You can even get a vehicle side plug with wire leads for easier connecting to the trailer wires. I would also recommend installing an inline fuse in case your wiring has a short to ground to protect the wires and battery.
Yes, stainless hardware is just fine for grounding. In fact, it will likely be better than the existing.
That said, yes, you can do all your testing with a 12-volt battery or 12-volt DC power source like a battery charger. If you connect the negative to the white pin, the positive will then be connected to any of the other pins (green, brown, yellow) to test. You can even get a vehicle side plug with wire leads for easier connecting to the trailer wires. I would also recommend installing an inline fuse in case your wiring has a short to ground to protect the wires and battery.
Yes, stainless hardware is just fine for grounding. In fact, it will likely be better than the existing.
Last edited by Tolyn Ironhand; 07-21-19 at 03:03 PM.
#2
07-21-19, 10:11 AM
probably could use some jumper wires hook up your ground and then apply power to each terminal. they do make testers with a power supply but they are expensive probably not worth the cost you could probably make your own also.
#3
07-21-19, 10:28 AM
Yea, I'm sure shops have a special apparatus just for this purpose and I agree probably expensive. Also I'm assuming to test the light all I really need is a 12 v source just to see if the light lite up. The function as to whether it's turn, hazard, or driving light is determined by the electronics in the tow vehicle.
Another quick question...In this case my middle light bar in the back got knocked off. All wires are in tact but the ground wire is no longer attached to the frame. They just used studs with a force fit type washer to hold the bar to the frame. I'm going use a screw and nut with lock washer. But since it's close to the ground, I 'd like to use stainless steel screws against plain steel frame. I'm sure that's OK for a grounding material?
Another quick question...In this case my middle light bar in the back got knocked off. All wires are in tact but the ground wire is no longer attached to the frame. They just used studs with a force fit type washer to hold the bar to the frame. I'm going use a screw and nut with lock washer. But since it's close to the ground, I 'd like to use stainless steel screws against plain steel frame. I'm sure that's OK for a grounding material?
#4
07-21-19, 10:51 AM
Group Moderator
A trailer with a 4 pin connector really only has 3 functions: Running lights (brown), which the taillights are in lower output mode and the side marker lights if present, and left (yellow) and right (green) full bright on. The tow vehicle only does the controlling of the tail lights whether to be constant on when breaking, or flashing when signaling, but the light is the same brightness. Of course, the running lights are also from the tow vehicle but they are just a single on-off switch.
That said, yes, you can do all your testing with a 12-volt battery or 12-volt DC power source like a battery charger. If you connect the negative to the white pin, the positive will then be connected to any of the other pins (green, brown, yellow) to test. You can even get a vehicle side plug with wire leads for easier connecting to the trailer wires. I would also recommend installing an inline fuse in case your wiring has a short to ground to protect the wires and battery.
Yes, stainless hardware is just fine for grounding. In fact, it will likely be better than the existing.
That said, yes, you can do all your testing with a 12-volt battery or 12-volt DC power source like a battery charger. If you connect the negative to the white pin, the positive will then be connected to any of the other pins (green, brown, yellow) to test. You can even get a vehicle side plug with wire leads for easier connecting to the trailer wires. I would also recommend installing an inline fuse in case your wiring has a short to ground to protect the wires and battery.
Yes, stainless hardware is just fine for grounding. In fact, it will likely be better than the existing.
Last edited by Tolyn Ironhand; 07-21-19 at 03:03 PM.
#5
07-21-19, 11:52 AM
Thanks Tolyn. Also about the color configuration.
That said I did a quick Google on wiring harness diagram. What they tell me is:
Isn't a side plug just the mating side to this? And the fuse should be placed at the white or negative terminal?
That said I did a quick Google on wiring harness diagram. What they tell me is:
vehicle side plug with wire leads for easier connecting to the trailer wires. I would also recommend installing an inline fuse in case your wiring has a short to ground to protect the wires and battery.
#6
07-21-19, 12:08 PM
And the fuse should be placed at the white or negative terminal?
#7
07-21-19, 12:12 PM
Trailers can be finicky because the grounds often aren't the best and you're working through the filaments as well as any sloppiness between the bulbs and sockets, but I have had some success with an ohmmeter or automotive type continuity checker, the kind with a battery and bulb in the handle, a spike, and wire with an alligator clip.
#8
07-21-19, 12:58 PM
No, the fuse should be on the supply or positive wire. That wire color code pictured is pretty much the universal standard.
AKA, yes, I use to have one of those back when I worked on cars.
Honestly I have forgotten a lot of what I use to know and with newer codes and electronics I'm a reluctant to try things. 
#9
07-21-19, 03:06 PM
Group Moderator
Sorry for the confusion. I posted the wrong color codes. I have edited my earlier post and Norm's post is correct.
Really the fuse could be installed on either side, positive or negative, but it is normally put on the positive wire. As long as there are only two wires coming off the power source current the flow through either one.
Really the fuse could be installed on either side, positive or negative, but it is normally put on the positive wire. As long as there are only two wires coming off the power source current the flow through either one.
#11
07-21-19, 05:53 PM
I have been running trailers like yours for 40 years, and I just want to add that most problems I have had over the years had to do with bad grounds, (unless I smashed one or more exposed tailler light assemblies) On the one I have now, which I built up from an old boat trailer, I made sure that I put the ground connection wire to the trailer in a very accessable place, so I can inspect it first every time.
#12
07-21-19, 06:27 PM
WML, I've had both types of problems. Smashed light assemblies and bad grounds. This latest problem where the middle light assembly was torn off and the ground was taken out. The assembly is still good. Just reattached and made sure there is a good ground. I'm not overly happy with the Carry-On brand trailer in terms of their wiring. Seems as though they could've done a better job. The trailer itself is good with tubular rails instead of angle iron.
#13
07-21-19, 06:38 PM
Well Norm, I can't speak for the Chinese light kit I bought from
Autozone to wire up this homemade trailer as far as quality, but unless I do a burn thru of the wires when repairing the frame etc it has held up pretty well. I should get some heavier wire and just re do it all, but hey it works, so I leave it alone lol
Autozone to wire up this homemade trailer as far as quality, but unless I do a burn thru of the wires when repairing the frame etc it has held up pretty well. I should get some heavier wire and just re do it all, but hey it works, so I leave it alone lol
Norm201
voted this post useful.
#14
07-21-19, 07:27 PM
Group Moderator
Suggestion as to what size fuse to use?
I have never been really impressed with any trailer wiring. Something always goes bad for one reason or another. One reason is they rely on the trailer frame for the ground path and the connections get corroded and damaged all the time. I am always fixing them along with tires and batteries.
OF course, I also have five trailers so that might be one cause.
#15
07-21-19, 08:31 PM
Group Moderator
When I had my mobile electronic store I would get many trailers to wire and repair. I didn't use the trailer at all for ground. I ran a dedicated ground wire and never had any problems. All connections were soldered and heat shrunk with glue type tubing.
#16
09-09-19, 08:06 PM
Pete, I know this is an old thread, but reading it again, I just wondered, since both my Chinese trailer light kits came with the white wire going to ground on the trailer, fastened to the frame with a sheet metal screw or bolt, and all the light assemblies are plastic, where and how you fastened your dedicated white ground wire to each assembly. From the look of it, the individual light cases grounded to the frame with metal sleeves that covered ( but were insulated from} the hot wires that ran the other light functions?
