Voltage on TOW Connector - Fiberglass RV


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Old 04-16-2014, 01:05 PM   #1
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Voltage on TOW Connector

This is related to my solar charging question.

I just checked the voltage across pin 1 (Black/12 v) and pin 4 (white/ground) on my tow vehicle (while running) and I measure less than 1 volt.

Can someone explain why only .5 volts?

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Old 04-16-2014, 01:12 PM   #2
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Bad ground? Try measuring from 1 to some other ground point.
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Old 04-16-2014, 01:21 PM   #3
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Charge line not hooked up, or fuse is blown? Check to see if there is an inline fuse near your battery or at the vehicle fuse box.
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Old 04-16-2014, 01:37 PM   #4
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Bad ground? Try measuring from 1 to some other ground point.
If it was a bad ground, would the trailer turn signals still work?
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Old 04-16-2014, 02:13 PM   #5
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The trailer lights are grounded to the frame. The car socket is grounded somewhere else. So, maybe they'd work because they have an alternate ground path.

Another idle thought I had is I bought a set of those blade fuses that light an LED in the fuse if it blows. That suggests to me that some small current must flow to the circuit even if the fuse is blown. The theory of this particular fuse is to highlight the one that is blown. It kind of defeats the primary purpose of the fuse but it is another way a very low voltage could be present. They were cheap and I bought some to play with.
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Old 04-16-2014, 02:25 PM   #6
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I just hooked up to the trailer and verified that turn signals, etc work.

I tried checking from 12 v on connector to ground on chassis, and it read 0 volts. I did find a black wire not plugged in to anything near the tow connector. I tried checking it for power and still nothing.
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Old 04-16-2014, 02:26 PM   #7
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As my understanding, your solar panels are located in trailer and you are trying to charge them with towing vehicle's battery/alternator( vehicle running)..i.e...via towing vehicle circuitry. If that is the case and that voltage drop measured as .5volts is correct, (supposed to be zero) then I guess either your vehicle ground or trailer ground has been loosen, otherwise, bad connection. Try to secure them well- sand frame to shiny, clean terminal shiny, bolt them tight and...grease them. Just my guess...
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Old 04-16-2014, 03:11 PM   #8
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As my understanding, your solar panels are located in trailer and you are trying to charge them with towing vehicle's battery/alternator( vehicle running)..i.e...via towing vehicle circuitry. If that is the case and that voltage drop measured as .5volts is correct, (supposed to be zero) then I guess either your vehicle ground or trailer ground has been loosen, otherwise, bad connection. Try to secure them well- sand frame to shiny, clean terminal shiny, bolt them tight and...grease them. Just my guess...
Two separate issues.

First is I want to connect solar panel through controller to 7 blade connector on trailer to charge battery. When I measured the voltage at the controller, it was higher than I expected. Renogy explained that is because it is open with no load.

Second, I wanted to see what voltage my tow vehicle was putting out on the 12 volt connection blade. I expected 12+ volts and I got 0. Either something is wrong or I just have no idea what I am doing. Both are equal possibilities!

What ties the 2 together is that I was trying to be 100% sure I had wired the connector correctly by comparing voltages - from what the controller is putting out on pin 1 to what the car is putting out on pin 1.
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Old 04-16-2014, 03:22 PM   #9
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Two separate issues.

First is I want to connect solar panel through controller to 7 blade connector on trailer to charge battery. When I measured the voltage at the controller, it was higher than I expected. Renogy explained that is because it is open with no load.

Second, I wanted to see what voltage my tow vehicle was putting out on the 12 volt connection blade. I expected 12+ volts and I got 0. Either something is wrong or I just have no idea what I am doing. Both are equal possibilities!

What ties the 2 together is that I was trying to be 100% sure I had wired the connector correctly by comparing voltages - from what the controller is putting out on pin 1 to what the car is putting out on pin 1.
...So I did misunderstand your purpose, in fact I understood it in...a reverse way. Sorry about that. Ab solar pnl charging or even its circuitry, I have no experience in it so I just pass it on. But separately your TV connector doesn't give out 12VDC at terminal it's supposed to then I think it definitely has fault there. Now the problem is at your tow vehicle harness alone. I guess either bad connection at that terminal/wiring or bad ground of your TV. If nothing could be found, I guess the problem lies within the connector itself, replace it. Just my thought...
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Old 04-17-2014, 06:08 AM   #10
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Do you have a factory installed tow package? On my Ford the fuse is under the hood while most items are under the dash. Just another place to look for the fuse. The problem does seem to be tow vehicle related to me. I get about 13.5v DC with the engine on, 0 volts with the key off. There is a fuse/relay to turn the charging current at the connector on/off. You reported that you check with the engine running so assuming the fuse/relay is okay and the ground is good it's a mystery to me. I suppose you could check each socket blade to a frame gound to verify the turn signals are getting 12v. If they don't then you're doing something wrong in measuring.

I've forgotten to switch the meter to DC on occasion...
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Old 04-17-2014, 06:21 AM   #11
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Do you have a factory installed tow package? On my Ford the fuse is under the hood while most items are under the dash. Just another place to look for the fuse. The problem does seem to be tow vehicle related to me. I get about 13.5v DC with the engine on, 0 volts with the key off. There is a fuse/relay to turn the charging current at the connector on/off. You reported that you check with the engine running so assuming the fuse/relay is okay and the ground is good it's a mystery to me. I suppose you could check each socket blade to a frame gound to verify the turn signals are getting 12v. If they don't then you're doing something wrong in measuring.

I've forgotten to switch the meter to DC on occasion...
I had my mechanic install the brake controller and do the wiring for the connector. I'll go by today and see what he says.
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Old 04-17-2014, 07:07 AM   #12
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You need one of these. I should start making them for sale. It plugs in between the trailer and the tow. It checks lights, brakes and provides voltage and amperage to the trailer from the tow. It was a winter project one year while dreaming about coming camping trips. I like the preparation for a project; the research, the procurement of parts (its full of "stuff"), etc. I even looked into making my own circuit boards as part of the next generation test box. Not that hard to do but circuit boards need really wide traces to pass through the amps it might see.

I think you can buy something similar but they're a bit pricey, especially for a one time user. But I don't think I've seen a pass-through tester. For that matter my box wasn't cheap either. But it kept me out of the pool halls one winter.

This photo shows the vehicle at idle and the refrig on DC. The green light indicates there is charging current at the trailer connector.

Oh, well, hope your installer has good news for you. Let us know what he says. I love a good mystery.
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Old 04-17-2014, 08:31 AM   #13
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On my ford truck there is also about 3 relays for the tow package including one for the charge circuit as well as a fuse. Can't find the relay in the wiring diagrams but I assume it only is turned on when the engine is running.
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Old 04-17-2014, 08:35 AM   #14
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Looks like I need to find a new mechanic.

He said to test battery, hook up tow to trailer, and test again. Battery read 12.86. Hooked tow up and battery still read 12.86. Hooked up shore power and battery read 13.6.

So problem seems to be in the wiring for connector. Even though he did the wiring, he is too busy to get to it until next week. Doesn't do me any good as the trailer and I will be at the beach.

ETA: They never hooked up the 12 v aux power. All 7 wires are connected to the connector, but the black wire is just dangling. Not connected to power.

Is anything needed to prevent the trailer batteries from draining the tow battery when stopped but still hooked up?
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