Is Diode Needed when Running Trickle Charge Wire Off 12 Volt Circuit for Lube Pump when Flat Towing

Question:

Maintaining a charge on tow car battery. I have a 6-pin on the coach and a 6-pin connector on the tow car which is a 2012 Toyota Highlander. It is for the lights on the tow car and to power a transmission oil cooler pump. For some reason, after a long tow trip 300-500 miles, the battery is dead in the tow car. I jump it off from the coach chassis batteries and its okay. I have tried to locate the power draw on the tow car battery, but haven’t any luck. I was thinking about connecting a wire 12ga from the hot lead going to the lube oil pump and attaching it to the tow car battery, to keep the tow car battery charged. Do I need a device inline to prevent the lube oil pump from taking power from the tow car battery? Thank you

asked by: Eddie H

Expert Reply:

Yes, you would want to install a diode such as # RM-690 to prevent power from flowing from the battery back to either the trailer connector or the pump.

Your vehicle may have some feature that stays powered on when the key is in the tow position.

expert reply by: Michael H