Towed Battery Charger Troubleshooting

A. There can be a few reasons why the battery is dying. You could have a bad cell in the towed battery, to much current draw from not pulling fuses, 12V might not be running from the motorhome batteries to the 7-pin at the rear bumper, there could be a blown fuse, or the Towed Battery Charger(TBC) could be defective. Try the following troubleshooting steps:

Test for 12V at the bumper of the motorhome

1. With the motorhome running, use a multimeter and touch the negative lead to the chassis and go around the pins on the 7-pin receiver at the bumper of the motorhome.

2. If you see hot 13+ volts, then we know the receiver is good and can proceed to test the umbilical.

3. If you do not find a hot 13+ volts, then a dedicated 12V accessory might not be run to the 7-pin or you have a corroded circuit lead. 

Test the umbilical

1. Plug in the umbilical into the motorhome's 7-pin.

2. Using a multimeter, touch the negative lead to the ground pin and go around the pins.

3. If you see hot 13+ volts, then we know the umbilical is good and can proceed to test the TBC.

4. If you do not find a hot 13+ volts, then the umbilical is bad.

Check for proper ground at the towed vehicle

The TBC relies on the ground for the wired light system that gets installed on the towed vehicle to complete the charging circuit. There are two types of wired light systems: the first has to be grounded and uses the existing light bulbs at the rear of the towed, the second is a self-contained loop that does not have to be grounded to the chassis and uses separate light bulbs. Check the back of the 6-pin receiver on the towed and make sure the ground goes to the chassis. If it does not, then you need to splice into the ground wire(usually white) and ground it to the chassis. 

Test the TBC

1. Check the glass barrel fuse on the side of the TBC. If the fuse is good, proceed to test the TBC.

2. With the umbilical unplugged from the towed vehicle, use a multimeter to get the towed battery's static voltage.

3. Plug in the umbilical to the motorhome and the towed vehicle.

4. Start the motorhome.

5. Use the multimeter on the towed battery's terminals and read the charging voltage. There should be an increase in the charging voltage over the static voltage. If you do not see an increase, then something is not working properly on the TBC.

A. There are a few possibilities for this. The first thing to check is the fuse on the side of the Towed Battery Charger. If that's not it, then refer to the troubleshooting steps from the question above.