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Troubleshooting Malfunctioning Taillight Converter on 1997 Toyota 4Runner


This is a 1997 Toyota 4runner. Im seeing a problem where both turn signals blink on a trailer when I activate either the Left or Right turn signal. I have tested with different trailers and see the same issue. Using a simple plug in tester that connects to 4Runners 4-Way Flat Vehicle Connector, showed that Lights, Brakes and Turn signals working correctly. I tested the ground it is seemed good. I then hooked up a voltmeter to the 4-way Flat Vehicle Connector, and that is where noticed that when I used the turn signal, the correct turn signal was getting 12V, but the other turn signal was getting 5V. This happens for both left and right turn signals. This explains why my simple test failed, but it does not explain the problem. Im thinking that the Trailer light converter box is going bad, but I would like your opinion. Thank you.


Expert Reply:

The problem you describe would usually make me suspect a poor ground connection on the trailer, but it seems you've eliminated that by trying other trailers on the vehicle. Just to be certain, check the spot on the vehicle where your converter grounds to the vehicle frame or chassis. Make sure this grounding point is secure and not corroded. To make absolutely sure, check the grounding points on the trailer as well (where the trailer connector grounds to the trailer tongue

Next, you'll need a helper and a circuit tester like part # PTW2993 or a voltmeter. Have a helper activate the right turn signal. Use the tester on the green wire on the INPUT side of the converter. If you get any voltage on any wire on the OUTPUT side of the converter, other than the green wire, your converter is shorted and should be replaced with a new one like part # 118341. Before replacing the converter, be sure to closely examine the wiring of your trailer. If there's a short in the trailer wiring that caused the converter to blow, you'll want to repair the problem, or you will continue to blow up converters.

I'll link you to our trailer wiring and troubleshooting help articles, which I hope you'll find helpful.

expert reply by:
Mike L

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