Trailer Circuit Tester?

D

Doryman

New member
I need to troubleshoot the wiring on my Tom Cat trailer. The brake lights are kaput so I got new LED tail lights at a discount from EZ Loader but some of the side markers don't work either. I thought I would rewire the trailer, but putting the wires on the outside of the frame members as per a previous discussion here. What I am looking for now is a device that will test the circuits by applying power to a pin and making the light come on. I found a number of devices with a Google search but if I understand the descriptions correctly, they test the truck circuits, not the trailer. I saw a homebuilt tester on casters at a local RV repair shop which makes me wonder if I am going to have to build one too. Would appreciate suggestions from those who have been there, done that.

Note: I have electric over hydraulic brakes so need to be able to test that as well.

Warren[/url]
 
I'm sure someone will point you in the right direction but I have seen one that will test both sides, the puller and the pullee. I'll do some looking and find it.

ON EDIT: Here's a Link to a bunch of different kinds. From simple to very expensive.

Charlie
 
Captains Cat":3it6shp9 said:
ON EDIT: Here's a Link to a bunch of different kinds. From simple to very expensive.
Click to expand...

That is the same page I found with Google. The expensive ones are obviously overkill and the inexpensive ones, if I read them correctly, are designed for testing the vehicle, not the trailer. Here is a typical description:

Features and Benefits: Plugs into the trailer plug Each LED light corresponds to the circuit being energized Provides an easy to connect ground terminal for trailer lighting set up Tests both 4 and 5 pin vehicle side connections for faulty wiring. LEDs light up to corresponding circuit. If LED does not light up, the circuit is not receiving power. Double sided unit allows the user to plug in-line with the trailer - leave plugged in while on the road. Made of hard ABS Plastic - durability for long life. 1 year limited Warranty. # INN7866
Click to expand...

So am I confused or am I right that the inexpensive ones do not do what I need?

Warren
 
I guess I'm just an old broken-down science teacher, but I can't see where you'd need anything other than a 12 volt battery (or power source), some leads, and a 12 volt light bulb in a socket as an indicator, although a VOM meter would assist in finding resistance and voltage drop problems.

Joe. :teeth :thup
 
I must be missing something very simple here...

If you pick up a cheap one to test/verify the vehicle outlet - and it passes - why can't you use the vehicle to test the trailer lights/brakes?
 
Sea Wolf & DaNag got it right. I just used a volt-ohmmeter, found the problem, bought a cheap fish tape at Harbor Freight, and rewired the trailer.
 
Aside from the fact that I am electrically-challenged, using the truck as the source means someone has to be sitting in the driver's seat and operating the controls.

Another issue is that the trailer is parked in a somewhat inaccessible spot since I only get it out twice a year, basically. I could use the truck but would rather not.

But you have answered my question, I think. I just apply 12v to each of the connections and see what lights up and doesn't?

Warren
 
The only controls that would at first thought require someone in the seat that you can't set up and leave running are the brakes to make sure that the brake lights are working. That too can be done without sitting in the seat. Just put 2 pipe wrenches on the brake pedal with the handles sticking toward the seat. They are heavy enough to turn the brake lights on and you can test away to your heart's content at the back of the trailer.

Jim
 
Doryman":2awu86u0 said:
Aside from the fact that I am electrically-challenged, using the truck as the source means someone has to be sitting in the driver's seat and operating the controls.

Another issue is that the trailer is parked in a somewhat inaccessible spot since I only get it out twice a year, basically. I could use the truck but would rather not.

But you have answered my question, I think. I just apply 12v to each of the connections and see what lights up and doesn't?

Warren
Click to expand...
Almost - apply 12 V to every connection but the ground wire! You can do this a number of ways. But the easiest would be to use a small 12V battery (like a lattern battery or a motorcycle battery). Hook the negative terminal to the ground (either via the plug or directly on the trailer) and hook the positive one to each of the other connections on the plug. If you buy or make a plug "extension cord" that is long enough, you can do this from the rear of the trailer so you can see the lights.
 
I like to keep a 12 volt garden tractor battery around the shop. You can connect a plug (like the truck connector) to this battery, posative wire at a time, plus ground, and use this as a source. I made a circuit tester, with a 12 volt bulb, with leads and alligator clips soldered on. Of course use the voltmeter with clips also.
 
Your emergency flashers will light both the tail lights and the brakelights all at once .It wont do the clearance lights [sidemarkers] but simply turning the headlights on will do that . No pipe wrenches needed. There are fuses for the trailer harness under the hood Warren , on the left side , under a black plastic cover that snaps off easily. Check the diagram inside the cover and check all the fuses that say trailer on them . I find them blown frequently . They are separate from the vehicle light fuses.
Marc
 
Marc , Yes they are. I was stumped as to why my lights would not come on. I had checked the fuses, and everything else, three times. then some one told me that new trucks have seperate fuses for the trailer lights and thats where I found the problem.
 
I lifted the ideas of some others, and then got really lazy. Here's what I did. First, got another vehicle-trailer 4plug connector, and used the lawn tractor for a power source. That was a lot better than having to back the tow vehicle up to the trailer. Then I got really lazy, and asked the obvious question: where can I find a 12v battery that's always near the boat, and easy to hook on to? Answer: gee, how about the two that are always there!

So, with that great revelation, I rigged up a wiring harness with a cigarette socket on one end, and a vehicle-trailer 4plug connector on the other. Two conductor wire is used from the socket. One wire is connected permanently to the short ground pigtail at the 4plug connector. Each of the three other pigtails from the 4plug connector have an insulated spade connector. The second wire from the cigarette socket has a mating insulated spade connector, so that it can be connect to any of the three 4plug wires, one at a time.

All you do is open the starboard window, plug into the cigarette socket, drop the rest of the harness out the window, connect the vehicle-trailer 4plug to the trailer harness, and then, one at a time, energize each of the three trailer wires.

This won't tell you if you have a problem with your tow vehicle's trailer lighting controller, but it does let you see if all of the trailer's lights are functional. That's enough for me.
 
Hey Warren! Do not feel bad about being electrically challenged.. I took my 2005 Excursion to a new shinny floor Ford dealership who had been in business in an old dirty building for 30+ years. They went stupid when the shinny floors hit them. Needed my oil changed and my electric over hydralic breaks on a new trailer were not working, but they worked on other's truck...so, felt sure it was the truck. They said they had a new fancy device just for checking the 7 pin connector... and said my truck was fine, charged me $45.....and still no trailer brakes... So... my C-Brat friend Terry from Attica NY...on LAST DANCE was with me... and out under the shade tree, we found with a very inexspensive push it in the wire and if it is hot, it lights up...if it does not... it is not hot. Well....the "always on" top center pin was not on... So... often the most simple testers are the best. If it's hot its hot....if it's not...well..it's not!!

Happy lighting!

Byrdman
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