Need Help with Socket Tester

[Capebuild]

Hello. The other day I had a Tekonsha P3 Brake Controller installed in my Subaru Outback. Since I don't yet have my lights hooked up on the trailer, I wanted to
test the 7 pin connector that was installed with the brake controller. To do this testing I bought a Curt socket tester (see attached photo). All the LEDs on the tester
illuminate when they're supposed to with the exception of the BU labeled LED, which is the tester for the "back up light or auxiliary power". The instructions for the tester
say this LED should illuminate when the tow vehicle is put into reverse. It does not illuminate so asking if anyone has any insight into that and why it might not be illuminating...
and whether there might be an issue with the installation wiring. I have no experience with this sort of thing.

Thank you for the help.

John

[JunkMan]

I don't think the backup lights are normally wired when a harness is installed. That port is used for auxillary power most of the time, but unless you asked for either of those to be wired,tbey probably left it disconnected. I wou!d check with tbe shop that wired it and ask if it was used, my guess is no.

[Capebuild]

Thanks for your help, JunkMan.

I think I figured out what the issue is.... when the brake controller was installed and mated up with the 4 pin flat connector that was already on the vehicle, that is where the wiring gets the lighting connections (eg. turn signals, brake lights, etc.)....... since there is no back up connection on a four pin connector, there would be no back up connection translated to the 7 pin. If my 4 pin flat connector were a 5 pin, that would probably have a back up connection which could then have been translated to the 7 pin.

John