Just returned from a vaction in Ft Wilderness.  Had a wonderful time visiting Cousin Mickey.

On the trip down, I stopped at a rest area at night to run the engine and circulate the transmission fluid in my 03 Honda Element (Automatic Trans).  The battery was dead.  I chalked it up to having left the blower fan on.  The key must be left in the "On" positon so the steering wheel is unlocked, but the engine is off.

Used the car to run around all week and it started fine.  On the ride home, my periodic stops to circulate the trans fluid everything worked fine.  Later, driving into the night, with the lights on, the battery again went dead.

My car has the installed light system hooked up to the car tail lights.  There are diodes in the wiring to prevent feedback.  My question is, can a diode go bad and enable the lights to draw from the engine battery?

Since I've been home, the engine starts and runs fine, so I can safely say the battery is not the problem.  I've had the wiring in place for 3 years and this is the first time I've had a problem.

Am I right to suspect the diode(s) as causing the problem?

Best Regards!

Hi Paul:

I wouldn't suspect the diode.  In any event it can be tested as described by a previous commentor.  The diodes are installed to prevent power from your tow vehicle from feeding back into the wiring of the toad.  In some of the newer vehicles, with computers and such, it can damage the toad if this is occuring.  If the diode were bad the power from the tow vehicle would feed back into the circuitry of the toad and unless something in the toad was shorted to ground as a result of the shorted diode there would be no ill affects on your battery.  If something were shorted in the toad it would stay that way even when not connected to the tow vehicle and the battery in the toad would run down even when not being in tow.   Since you say you have used the toad this way for 3 years without a problem in the past, I would suspect the battery in your toad is on the verge of failing.  If that battery is 3 years old too, it could be getting to a point where it cannot feed the toads internal circuitry while in tow like it did when it was new.  Having to leave the ignition switch in the "on" position does put power to some circuits in the toad independent of any power from the tow vehicles system.   You can have the battery load tested at an Auto Zone store free of charge.  Hope you find the problem!

Alan,

Thanks for the idea.  I'll get the battery load tested to be sure.  The battery is apporaching 4 years old, so it will be a good idea to replace it if it is even less than perfect.

What I'm curious about is why it only happens at night with the lights on.  I tow mostly during the daytime, so any battery weakness would manifest itself more in the daytime.

Let you know what I find.

Best Regards!

Hi Paul:

You didn't mention what type of car you tow but I did some investigations on our Ford Explorer Sport Trac after reading of your problem.  Our Explorer has a position on the head lamp switch that is for automatic operation.  We leave the switch there so that when it gets dark the electronics senses the light level and automatically turn on the lights.  If I leave the ignition switch in the "on" position without the engine running and have the light switch in the "auto" position, the lights will come on when it gets dark and run the battery down.  From now on we will tow with the light switch in the "off" position.  There maybe other things that come on automatically when it gets dark that would also contribute to draining the battery.  It will just take some digging to find out.  I hope you find the problem.