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I have a harbor freight tag-a-long trailer and having difficulties with getting the lights to work. I have an Addon trailer wiring harness w/isolator relay. I can verify that this works by using an ohm meter. THe issue seems to be with the 5 to 4 wiring harness convertor. The running lights work, but no brake lights or turn signals. I have tried 2 different types of convertors, a Hopkins and a U Haul brand, both with the same results. Any ideas or suggestion on where to look?
 

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When I was wiring mine (a Piggybacker) I ran a temporary wire from the trailer frame to the bikes Neg battery to make sure there was no doubt. In my case, it was a poor/inadequate ground to the trailer. Other than that, not sure what else to say.
 

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Thanks I will check the grounds, the issue seems to be that I can verify all functions ahead of the converter, but only see voltage for the running lights after the convertor.
 

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Thanks I will check the grounds, the issue seems to be that I can verify all functions ahead of the converter, but only see voltage for the running lights after the convertor.
Same symptoms I had. That is what confused the heck out of me. I am like....now wait, I have to have GRD because the running lights are working. Turned out not to be the case. I just can't remember what I ended up doing to fix it.

Edit: Hey, it just came to me. There were some small inline fuses (5 Amp or 7.5 Amp) that I had blown and didn't know it....well, at least not until I found them. But by the time I actually found them I already had the temporary GRD inplace. So maybe the temp GRD didn't really do anything. Sorry if this messed you up.
 

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I checked the inline fuse and found it to be good, Without it the running lights do not function. I just cant understand why no voltage to the brake or turn lights. Makes me suspect the converter, but I have already tried two. Is there anyway that the converter can be checked? I guess I could try to apply voltage directly to it and then see if any output.
 

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I am not sure what else to recommend. I did drag this up. Might be worth a qucik read.

Troubleshoot Your Trailer Wiring


If you have a Modulite (powered converter), Converter, or T-One connector that is not working properly, you need to use a circuit tester to determine the source of the problem.
  • Check to make sure there is a signal going into and coming out of the converter or Modulite box without the trailer hooked up. The only part of the wiring harness that will typically go bad is the box, so you need to determine if a signal is making it to the box, and if so, is it coming back out on the correct wires. There are four possibilities:
    1. There is no signal going into the box, meaning something is incorrect on the vehicle.
      • Solve the problem by checking for blown fuses and then check the installation points. Use a circuit tester to check that the correct wires are tapped into, the wiring harness connectors are plugged into the correct vehicle connectors, and check that connectors are plugged in all the way.
    2. A signal is going in and coming out on the appropriate wires, then there is a problem with the trailer wiring.
      • Solve the problem by inspecting the wiring on the trailer to make sure all of the connections are correct and ground wires are connected properly. Most likely, the ground wire on the trailer is not secured properly. A trailer wiring system is grounded to the frame near the coupler and each light also needs to be grounded. If there is not a white ground wire coming out of a trailer light, then the light is grounded through its mounting studs. Too much paint, dirt, or rust can cause bad grounds, so make sure the ground is secured to the bare metal frame. Also look for pinched or cut wires, these are often found when wires are routed above suspension components or behind taillights
    3. If a signal is going into the box and not coming out or a signal is going into the box and coming out on the wrong wires the ground on the vehicle may not be connected properly. If the white ground wire is not installed properly on the vehicle, then the green and yellow wires will not carry signal coming out of the box.
      • Solve the problem by checking to make sure the ground wire is installed properly on the vehicle. To make sure you have a suitable ground, first connect the circuit tester's ground wire to the same location as the ground wire on the wiring harness. Then test the signal going into the converter or modulite box. If there is no signal, connect the circuit tester to another grounding location such as the exhaust pipe. If a signal is present, the grounding location for the wiring harness is bad, and a new location needs to be found. On a few vehicles, the frame and body components are not grounded. In these rare instances, look for a ground wire coming out of the license plate light.
    4. Due to extensive testing and quality control, it is very rare that a new wiring harness will be defective. If the wiring harness worked properly when installed but then went bad, there is a strong possibility that it has shorted out because of a problem with the trailer wiring. Make sure to correct any trailer wiring problems before installing a new wiring harness.
Converter Shorting Out


When too many amps are drawn through the converter box, it can be shorted out. The possible causes are:
  • Too many lights on the trailer. Each incandescent taillight draws about 2 amps and side marker lights typically draw about 0.5 amps each. Most converters allow up to 4 amps to pass through them. A standard converter cannot have any more than 1 taillight on each side.
  • Trailer connectors get wet, causing too many amps to be pulled through the converter. Water can unite all 4 wires on the trailer connector causing it to draw too many amps. This often happens when a boat trailer is backed into water with the trailer wiring still connected to the vehicle.
    • To solve the problem of connections getting wet, always disconnect the trailer connections before backing into the water. Also, covers can help prevent water from getting into trailer connectors when it rains or when a vehicle is taken through the car wash.
  • Bare wires touch each other or the trailer frame. This causes too many amps to be pulled through the converter box. The coating on trailer wires can wear thin, often at the connection to the trailer's taillight or where the wires pass over the trailer suspension. If wires are hung too loose, they can get pinched and smashed between the trailer frame and suspension u-bolts.
    • To solve the problem inspect the trailer wires and replace any that are damaged or frayed.
Weak Ground


If you find some, but not all, lighting functions work properly you may have a ground problem. In this situation a weak ground is just strong enough to provide some lighting functions but not all. When the taillights and brake lights are used at the same time, it creates the maximum amp load of the lights on the trailer. If a ground problem exists, it will show at this point. The places to check grounds are as follows:
  • The connector on the vehicle should have a ground wire secured tightly to a clean surface on the frame. A wire attached to the body or a surface with undercoating or rust can cause a ground problem
  • The connector on the trailer should have a wire from the connector secured tightly to a clean surface on the trailer.
  • Each tail lamp assembly at the back of the trailer also must be grounded. This is done in one of two ways.
    • The first is by a separate wire coming from the back of each tail lamp assembly being secured to the frame.
    • The second, and most popular, ground is achieved through the bolts of the tail lamp assembly. In this case, the lamp housing must be attached to the frame of the trailer. If the lights are mounted on wood or PVC material, the light will not receive ground.
  • The last possibility to explore is in the trailer design. If the trailer has a tilting bed, it is possible the ground is not passing through the pivot point resulting in a poor ground. The solution to this is to route a ground wire from the connector at the front of the trailer to each lamp assembly at the back of the trailer bypassing this pivot point.
 

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Discussion Starter #7
Thanks again! And very good information, I will go through and check everything again in the morning.
 

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4 to 5 converter

I am gathering all the components to change a Tag-along from a 4 to 5 hookup. I have a Rivco 5 wure plug on the bike and looked at converting my Rivco isolator to a 4 wire by using the 5 t0 4 converter. I researched it to death and if I remember corectly, the 4 wire converter has to go before the 5 wire isolator.

http://www.rivcoproducts.com/products/product.php?productid=524&cat=255&page=1

Check this Rivco converter out. it says it has to be wired in ahead of the isolator
 

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I had the same problem and fixed it with a u-haul 5-4 one. They had 2 different ones but only one worked. Make sure the u haul one has the stops combined with the turn.
Product # 13493
 

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Discussion Starter #10
Does anyone know if it is true that the 5 to 4 convertor must be AHEAD of the Add On wire harness w/isolation relay (PN 45-1819)? As Hog Wild stated this is true for the Rivco set up.
 

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I had a similar problem and the 5-4 converter had to be installed before the isolator. That solved the issues for me. I had tried two different converters prior to that, but was always trying to install them after I had installed the isolator.
 

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Discussion Starter #13
Just to update this thread. I did install the Hopkins 5 to 4 convertor ahead of the Add-On wire harness w/isolation relay (PN 45-1819) and everything worked correctly. The emergency flashers were more side to side flashing instead of both flashing on at the same time unless a brake lever was depressed. Thanks again to all for their help.
 
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