Trailer lights not working

5337 · Aug 6, 2018

Just picked up a 1994 Mazda B3000 2wd with a plug for trailer towing. No power at plug and found ground wire broken and repaired that. Checked power at the plug and now have power for both rear lights and running lights. I hooked up my trailer and have running lights but no signals. Unhooked trailer and hooked back up to my Jeep and lights work fine :icon_confused:

Don't know what to look for next...Heavy duty blinker fuse?

RonD · Aug 6, 2018

Most trailers use a 4 way(wire) setup
Ground
Parking lights
Left turn AND Brake
Right turn AND Brake

So turn bulb and brake bulb are the same, share 1 wire for each side

1994 Ranger/Mazda uses a separate Brake light bulb, so there is a 5th wire

You can get a Converter which will probably be best since it would convert trucks trailer plug in to match most trailers

And if current plugin on the truck is 4 wire then converter may already be installed, just not working, bad splice or ??

The converter(small black box) connects to 3 wires, left turn wire, right turn wire and brake wire, on trucks wiring, then has 2 wires OUT to trailer plug in, left turn AND brake, Right turn AND brake.
So converter combines the 3 wires into 2 wires with an electronic circuit that isolates each side so brake light doesn't cut off turn signals when both brakes and turn signals are in used at the same time

1994 wiring diagram here if you want to see wire colors: http://www.therangerstation.com/forums/showthread.php?t=162630
Download diagram from post #3

5337 · Aug 6, 2018

Thanks Ron, It has the converter installed underneath the truck. The ground wire was broken and I repaired that by mounting it under a bolt to the bumper. I have power to the 4 prong plug on left signal, right signal and running lights. I have tested with a trailer test plug from Harbor Freight and with my tester and all are working as it should until I attach trailer plug, then no lights on trailer. Running lights work but no signal lights.
I checked the trailer wires and then hooked them up to my Jeep and they work fine.

Ground wire looks to be 16-18 Gauge wire and I loosened the bumper bracket bolts and attached the ground wire.

RonD · Aug 6, 2018

What about brake lights?
Do they work on the trailer when hooked to the Mazda

Also plug in the Tester into the Jeep and see if it works the same

ericbphoto · Aug 6, 2018

This is strange. Almost sounds like either A. Trailer has single element bulbs installed or B. Mazda has bad flasher that doesn't like the extra load of the trailer lights. But neither scenario fits perfectly with the symptoms reported. One other question. Does the trailer have regular incandescent bulbs installed or LED's?

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5337 · Aug 6, 2018

Thanks Eric, the bulbs are duel element and work fine behind my Jeep. Just used it this evening to haul my zero turn to mow a yard. I'm stumped on this one because I have power at the 4 prong plug on the Mazda, but when I plug the trailer in I have no turn signals or brake lights but have running lights. I'm leaning toward the blinker. Might try a heavy duty and see if that helps. :icon_confused:

ericbphoto · Aug 7, 2018

the bulbs ... work fine behind my Jeep

That's the weird part. I'm leaning toward the flasher being the problem. Quite a puzzle.

Ranger850 · Aug 7, 2018

Wrong bulbs?

4x4junkie · Aug 7, 2018

My guess is that the converter is bad (has high resistance). This would pass the tiny amount of current needed for a meter or tester to see voltage, but not enough to actually light up a bulb (I assume the lights on the truck itself are working correctly).

I've had such converters just up & quit on mine, proving they aren't exactly the most reliable.

5337 · Aug 7, 2018

Thanks 4x4junkie, I worked on it today and thinking the same as you. Gonna get a new converter and try that. I'm only getting 10.3 Volts to the plug and I'm assuming it should be 12 Volts.
Yep, lights on truck work fine and so does trailer when it's hooked to my Jeep.

5337 · Aug 9, 2018

Thanks 4x4junkie, you were right, it was the converter. Picked up a new one and problem solved. Did have to add a heavy duty flasher because the signals blinked to quick.
Thanks again!

RonD · Aug 9, 2018

Good work

ericbphoto · Aug 10, 2018

congratulations and thanks for sharing.

5337 · Aug 10, 2018

4x4junkie · Aug 11, 2018

Glad you got it working.

×2 Thanks for the update.

Trailer lights not working

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