No 12v from TV - Fiberglass RV


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Old 10-19-2018, 04:32 PM   #1
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Question No 12v from TV

I have no evidence that 12V feed is reaching my Casita.

I have a 7 flat pin connector. Turn signal, brake lights and electric brakes all work perfectly, but it seems that no 12V power is reaching the trailer battery or the trailer's 12V circuits.

Using a multimeter, I find no current from ground (1) to aux power (4). This is true with ignition on or off and with the engine running.

The 2004 Trail Blazer tow vehicle was factory wired as part of its towing package.

What are the probable causes, or cause of this lack of current?

Thanks.

Jim

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Old 10-19-2018, 04:43 PM   #2
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Originally Posted by James Davis View Post
I have no evidence that 12V feed is reaching my Casita.

I have a 7 flat pin connector. Turn signal, brake lights and electric brakes all work perfectly, but it seems that no 12V power is reaching the trailer battery or the trailer's 12V circuits.

Using a multimeter, I find no current from ground (1) to aux power (4). This is true with ignition on or off and with the engine running.

The 2004 Trail Blazer tow vehicle was factory wired as part of its towing package.

What are the probable causes, or cause of this lack of current?

Thanks.

Jim

Most 12 volt system are fuse protected. Depending on many different trailer makes and wiring configuration, some were just wired to the auxiliary battery on trailer and for most the 12 volt feed is feeding to the 110/12 volt converter and then back to the trailer battery. I had the same problem this spring and could not figure why the trailer had no 12 volt power. I traced the wiring from the vehicle trailer plug to inside the trailer and after many gymnastic body contortions, I was able to locate inline fuse that I never knew existed.
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Old 10-19-2018, 04:46 PM   #3
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was the ignition on and engine running when you did this test? many factory tow packages won't power the 7'blade until the vehicle alternator is charging

on my 2001 ford E150 we bought new, the tow package included a relay and fuse in a baggy in the glovebox, these had to be plugged into the main relay/fuse panel under the hood to provide tow power.
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Old 10-19-2018, 04:48 PM   #4
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Sounds like that's worth a look, but I have no voltage on the TOW VEHICLE, so maybe there's a fuse on that side too... That would make sense.
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Old 10-19-2018, 04:49 PM   #5
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Sounds like that's worth a look, but I have no voltage on the TOW VEHICLE, so maybe there's a fuse on that side too... That would make sense.
the fuse and relay I am talking about are on the tow vehicle side.
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Old 10-19-2018, 04:51 PM   #6
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was the ignition on and engine running when you did this test? many factory tow packages won't power the 7'blade until the vehicle alternator is charging

....
Yeah, as I said in the first post, engine running or not, no juice.
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Old 10-19-2018, 04:51 PM   #7
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"Tow package" means different things to different people (and companies). It is quite possible that a charge line is not considered part of the tow package for that vehicle. You would have to research it to make sure it is included, unless it was working and now it is not.
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Old 10-19-2018, 05:09 PM   #8
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Using a multimeter, I find no current from ground (1) to aux power (4). This is true with ignition on or off and with the engine running.
If you were truly measuring current between these two points, that is, using the ammeter function on your multimeter, then you were placing a short between the two points which would certainly pop a fuse or breaker. Perhaps you ment voltage?

Many charge lines are relay activated. The relay will be fused. That's where I would start.
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Old 10-19-2018, 05:23 PM   #9
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the fuse and relay I am talking about are on the tow vehicle side.
Thanks.

I found what seems to be the fuse for that circuit (30 amp). Fuse not blown, but no power in fuse socket with the engine running. So, there must be a relay I don't know about. Will have to research it.
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Old 10-19-2018, 05:25 PM   #10
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If you were truly measuring current between these two points, that is, using the ammeter function on your multimeter, then you were placing a short between the two points which would certainly pop a fuse or breaker. Perhaps you ment voltage?

Many charge lines are relay activated. The relay will be fused. That's where I would start.
good catch. i read 'voltage'. if his meter was actually in a ma or amps mode, it would have blown a fuse inside the meter, which disables the amps/milliamps modes. those are very fast-blow fuses.
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Old 10-19-2018, 05:30 PM   #11
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good catch. i read 'voltage'. if his meter was actually in a ma or amps mode, it would have blown a fuse inside the meter, which disables the amps/milliamps modes. those are very fast-blow fuses.
Yes, I was measuring voltage, but thinking flow, both of which were zero.
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Old 10-19-2018, 05:30 PM   #12
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Thanks.

I found what seems to be the fuse for that circuit (30 amp). Fuse not blown, but no power in fuse socket with the engine running. So, there must be a relay I don't know about. Will have to research it.
you measured the voltage from either side of the fuse socket to a good ground nearby? you can't measure the voltage across the two fuse pins, because there's no load plugged into the trailer socket.
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Old 10-19-2018, 05:44 PM   #13
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you measured the voltage from either side of the fuse socket to a good ground nearby? you can't measure the voltage across the two fuse pins, because there's no load plugged into the trailer socket.
Ah. Right you are. I'll check again.
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Old 10-19-2018, 05:57 PM   #14
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OK....I get a 12V reading on one leg of the fuse socket, so, why do I get nothing from 4 to ground at the pigtail socket? Got to be another fuse or relay, or????
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