Convert Motorhomes 4 Way To 7 Way And Install Charge Line For Towed Vehicle Battery

Updated 02/09/2021 | Published 02/05/2021

Products Featured in This Question

10 Gauge Wire - Blue Primary - Per Foot

(109)

$1.87

Buyers Products Trailer Connector Adapter - 4-Way to 7-Way RV and 4-Way Flat

(208)

$20.76

40 Amp In-Line Circuit Breaker - Perpendicular Mount Bracket

(101)

$9.98

Roadmaster 4-Diode Universal Wiring Kit for Towed Vehicles - 7-Way to 6-Way Straight Adapter Cord

(3579)

$181.68

Roadmaster Battery Charge Line Kit for Towed Vehicles

(1454)

$47.02

12 Volt Outlet Kit, 20 amps

(407)

$46.07

Question:

I have 4 wires coming from motorhome

asked by: George L

Expert Reply:

If you do not have a 4 way flat and just have 4 wires at the back of your motorhome, then use Hopkins Endurance Quick-Fix Replacement 4-Way Flat Trailer Connector w LED Test Lights - Vehicle End # HM48190. This will connect your 4 wires to a 4 way flat plug. Once you have a 4 way flat, you can convert to 7 way with Buyers Products Trailer Connector Adapter - 4-Way to 7-Way RV and 4-Way Flat # 337TC1474P.

Your 4 way flat will plug into the 4 way harness on this adapter, then you will need to ground the white wire to your motorhome. The adapter's black wire should be connected to the positive terminal on your motorhome's battery using 10 Gauge Primary Wire # 10-1-1. You will want to add 40 Amp In-Line Circuit Breaker # 9510 in the wire before connecting to the battery.

Now you can use Roadmaster 4-Diode Universal Wiring Kit for Towed Vehicles - 7-Wire to 6-Wire Straight Cord # RM-152-98146-7. This will connect to your motorhome's 7 way and be mounted on your towed vehicle's front bumper for light signal output and charge line output. This kit comes with everything to connect your RV lighting wires to the towed vehicle's lights. Use Roadmaster Battery Charge Line Kit for Towed Vehicles # RM-156-25 to keep your towed vehicle's battery charged/maintained. One end connects to the 12v wire on the bumper-mounted kit mentioned above, and the other end connects to the towed vehicle's battery.

In order to use a supplemental braking system, use 12 Volt Outlet Kit # RM-9332 which will connect to the towed vehicle's battery and be ran into the cab to power the supplemental braking system. I have attached demonstration videos for these products.