Tow Vehicle 7-Way Plug Emulator

[DougE]

This was my rainy day project. Build a test unit to replicate the trailer plug on my tow vehicle. I can insert the 7-way from my trailer, hook up a battery or charger to the side posts and check each of the trailer circuits. Everything was pretty much available at Home Depot.

[cooperrobt]

Very nice. I like simple too. I had an old 12 volt 11ah battery in the garage and it seems to have enough power to light up the led tail lamps. Thanks for your help.

[DougE]

OK, here's the interior wiring, ugly as it is. I'm a proponent of KISS.

[DougE]

copperrobt - My old brain is a little foggy but I think I tried it first with a 2 amp maintainer and it didn't have enough poop to light up the LEDs. Everything works OK with a 12 amp charger.

[cooperrobt]

Thanks for your quick response.
The reason that I asked is that I just recently built one of these and although the incandescent running lights illuminate, the LED tail lights do not (they do work with the truck hooked up). I was thinking that the 5ah battery is too small and perhaps a 10ah battery would be a better choice (the house 6v batteries blow the inline fuses when the test box is connected to these).

Moderator edit to re-size picture to forum recommended limit of 640px maximum width.

[DougE]

Here's a simple wiring diagram:

[DougE]

cooperrobt - all I'm doing is putting 12v on each circuit so it doesn't matter what kind of lamp is on the circuit. I've hooked up all the switches to a common hot wire and have taken the ground directly to the 7-way. Then each switch activates one prong on the 7-way.

[nremtp143]

Impressive!!!

[cooperrobt]

Can this be used on trailers with LED tail lights?

[DougE]

You could probably sneak an amp meter in my little 4" cube box but it would take some serious wire management to make room for anything else. You can use a compass to see if the brake magnets are actually actuated.

[DrewE]

It looks very nice to me, too.

If I built one, I might put a little ammeter in, which would be useful for finding partial shorts and disconnected brakes and so forth. For that matter, a couple of banana jacks to hook up a multimeter would suffice, with a jumper wire or switch to bypass them at other times.

For that matter, while I'm dreaming, I might also put in a bluetooth or wifi unit and write an app to control it from a smartphone so that walking around and poking at the screen would make the trailer lights go on and off and save having to wander back around each time. The ammeter seems like less work, though.

[D_E_Bishop]

wanderingbob wrote:
Amazon sells one for eight bucks .

The $8.00 tester is for testing the TOW VEHICLE end, the TRAILER end testers are in the $200 to $400 range.

[DougE]

wanderingbob - Link? I could use a new brain!

[wanderingbob]

Amazon sells one for eight bucks .

[DougE]

JaxDad - apparently your brain is better than my old one. I can't remember the arrangement of pins on a 7-way and usually have to print out a diagram to know which position should have which result. Fortunately most stick to a common pin location specification but less consistent is the wire color coding. I wire all my vehicles to the most prevalent specification and using my box takes my brain out of the mix.