I recently had the need for a 7 wire tester for our Inspections. All Towables (Travel Trailers, 5th Wheels, Popups, etc.) use an umbilical cord that attaches to the Tow Vehicle. The umbilical is used to illuminate the turn signals, brake lights, but most importantly, they activate the electric brakes if it is equipped. Sometimes, the Trailer is setup to charge the Trailer Battery from the Tow Vehicle.
I check these anytime I hook up our RV and go camping. Once the Trailer is hooked up, it’s actually pretty easy. Turn the hazard lights on and go walk to the back and make sure the lights are blinking. To test the brakes, I just set the brakes on the controller (in the Truck) and see if the Trailer brakes will stop us.
But when we Inspect an RV, we are supposed to test these features and make sure the client gets an RV that is working correctly. But since we pride ourselves on being professional, it seems jenky to me to plug a Client’s umbilical into my Truck. Suppose the RV has a wiring issue and causes me a problem? Or worse yet, suppose my Truck has an issue and causes the client’s RV an issue? Either way, it’s a Liability, not very professional and it’s off-brand.
So there are commercially available 7 wire testers and I was looking at buying one. When I was checking them out, I thought to myself, “It’s just a switch box and a battery!” Essentially, you’re powering the circuit from the on board battery (or the Trailer battery) and making the lights come on. So I pulled up Amazon, ordered a few parts that I didn’t have and decided to put this together a few days later. I’ll add that I used to be an Electrician when I was in the Navy and I’m pretty handy around the house. So this was well within my wheelhouse, so to speak.
I used a cordless drill battery adapter, 7 wire connector, a meter and a few switches. I use the meter to test the circuit for Electric Brakes. I can see how much current the brakes are using and since I know how much it’s supposed to use, I can decide if they are working correctly. I’m pretty happy with the results and it works as good as I thought it would.
As a side note, Kathleen pointed out the 7 wire tester only had 5 switches. There are 5 circuits, but you need 2 wires for the battery power. Also, I’ve yet to find a Trailer that had Backup Lights, but I’m still going to test for it. FYI, I don’t plan to make these and sell them, but if you would like the schematic or want to know which parts I used, just ping me.