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Dim Tail Lights on 2007 Toyota Yaris Hatchback When Flat-Towed Using Roadmaster Diode Kit # RM-154


I installed this system on my 2007 Toyota Yaris Hatchback. I only used the tail/stop light on the Yaris and didnt connect to the separate turn signal bulbs. I just used the stop light for turn signal. Everything works perfectly but the lights on the Yaris are really dim when hooked to the motorhome. I checked the voltage at the rear of the motorhome and through the connector cable and the voltage is good. Do the diodes cause a voltage ? I didnt have time to take the taillights out and check voltage there. I did check the grounds and they are all good. Do you have any suggestions? Would led bulbs remedy the problem? Thanks for your help.


Expert Reply:

Thank you for providing a detailed description of your lighting issue and of the troubleshooting steps you have taken so far.

Diodes should not cause a voltage drop if they are operating properly. You can test whether the diodes are the problem by apply a voltmeter to the upstream and downstream wiring with the MH engine running. If you detect close to 13 volts going into the diodes but substantially less on the output side then the diodes may be defective. There could also potentially be a short somewhere allowing power loss. The ground connections, although already checked, are the most-common cause for the issue you describe. You can try moving the grounding point to a new clean bare metal surface to see if this remedies the dim light output.

Certainly switching the vehicle tail lights over to super-efficient LED types is a great way to get more light output from the available voltage. LEDs use about 1/10th the power of incandescent types. The link at right will take you to our main page for LED replacement bulbs. You can pull one of your existing bulbs to obtain its referenced number and then check for availability of an LED equivalent.

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