Trailer light issue

Just installed an aftermarket trailer wiring/converter combo, and only the marker lights work to the trailer. Checked the trailer plug and the marker lights have 12v but the turns only have 7-8v, removed the aftermarket t-connectors and checked the factory harness-same. Tried it on another trailer-same. Ran a ground from the battery to the harness also. Anyone seen this before?

 

Unless you are testing the blinkers with an oscilloscope, you can get low voltage readings. Typically, a voltmeter will provide you an average voltage over some period of time. The period of time can differ based on the design of the voltmeter. Remember that the blinkers are cycling between 0 and 12 volts, so the reading you get should be bouncy and somewhere in between. You are getting 7-8 volt, which is consistent with a voltmeter reading of a blinker.

Try checking the voltage of the signals with the blinkers OFF and the brake pedal pressed down. That should give you a constant voltage between 12.5 and 14.5 volts. If you have voltage, but no LIGHT, it means that your bulbs are bad or not making proper contact.

Make sure also that you are testing with the voltmeter's negative lead touching the actual bulb socket (or white pin on the plug if you're testing there). If you are testing the positive in the socket against the negative somewhere else, then you could be experiencing a disconnected negative to the socket. Check for continuity between the negative terminal of your truck battery and the bulb socket on the trailer.

 

Careful, you might easily burn out a lot of fuses if the electrical load of your trailer is too much. LEDs have little loads so it's no big deal but regular incandescent bulbs draw a lot of current and do "funny things" when they are hooked up to your truck and lit. Much easier to go with the Toyota factory towing harness that is fuse protected. If you "pop" its fuse then you know there is either a bad ground, a short somewhere in the trailer wiring, or too much current draw from the number of incandescent lights on your trailer (if equipped). I converted my two-place snowmobile/motorcycle trailer to all LEDs and had to also rewire it from mouse damage and it works flawlessly now.