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Old 09-17-2015, 01:11 PM   #1
3 Rivet Member
2016 30' Classic
Santa Rosa , California
Join Date: Apr 2015
Posts: 143
Need help with strange test results on TV 7 way plug

My wife and I recently completed our first long trip (9,300 miles) with our 2015 FC 20ft and TV (BMW X5). On the return leg, our AS running lights stopped working. I used a voltmeter to test the TV's 7 way plug. Some results are expected, but I would like input on what the others may mean.

I get 12V between the power pin (upper R) and the neutral/ground pin (lower left) as expected, whether ignition is off or on.

With the TV R or L turn signals flashing, I show swings up to 12V for the R or L turn signal pins (right and left pin position, respectively) and the neutral pin. Expected.

With TV headlights/tail lights on, I only see about 3-4 V on the running lights pin (upper left) and neutral pin. This seems wrong - shouldn't I be seeing 12V here too? If so, I expect this is why my AS running lights aren't working.

However, even stranger....with the TV ignition switch and lights OFF, I still see about 3-4 V when I retest each of the turn signal pins, and the running light pins. Furthermore, I get 12V at the electric brake pin! Is any of this normal?

My hitch/trailer serviceman originally told me he had interfaced my BMW wiring with the 7 way plug wiring using some sort of electronic module, apparently designed to protect my TV circuits. With all this apparent weirdness in the 7 way plug test results, I'm suspecting the module has failed.

I would surely appreciate some expert answers to my questions....and please tell me which of my interpretations are valid, or not. Thanks!

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Old 09-17-2015, 01:56 PM   #2
Rivet Master
Southwestern , Ohio
Join Date: Nov 2006
Posts: 1,669
I can't tell you why your running lights aren't working but I suspect the reason you are seeing 3-4 volts on pins that should be showing zero is that you are seeing leakage current through the electronic switching devices with your high impedance voltmeter.

In troubleshooting 12 V wiring it's handy to have a plain old test lamp--12 volt bulb with leads attached. If you hook the test lamp between one of the pins showing 3-4 volts and ground I bet it won't light, even dimly, and your meter won't show any voltage either.

By the way, when you say "running lights" do I assume correctly that you mean both the tail lights and the clearance lights on the trailer? They are all on the same circuit. So if, say, the tail lights are working but the clearance lights are not, there's probably a blown fuse in the trailer.

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Old 09-17-2015, 06:53 PM   #3
3 Rivet Member
2016 30' Classic
Santa Rosa , California
Join Date: Apr 2015
Posts: 143
Both the clearance lights and tail lights on the Airstream are not working. Brake lights, turn signals and electric brakes are all working. I will get my hands on a test light and repeat the tests. Thanks.
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