Help to complete a 12 v circuit

Anything electric, AC or DC

Help to complete a 12 v circuit

Postby gene so » Sun Mar 11, 2018 4:46 pm

I am finishing the wiring of my galley and thought it was complete when I had two AC receptacles and a switch for the 12 v pump for the water tank wired up. The back wall was installed andonly then I realized I had not installed the 12 v receptacle.
I checked the group of wires coming up from the false floor that holds all the wires from the Inverter to the various portions of the trailer. in that group I located the black wire which was not hooked up, this would have been the "hot wire" for the receptacle. I had four white wires in that group. None pulled out of the sheath. Although the one which was not hooked up, should have. So, I did not know which was which.
I got out my 12v electric starter and my volt meter. I attached the volt meter red line and also my existing black wire for the receptacle, to the "hot" cable of the electric starter. I then attached solderless connectors to all the white wires and hoped to use the voltmeter to discover which white wire was the correct one to complete that 12 volt circuit. None of these wires solderless connectors, when I touched with the voltmeters' other electrode, moved the gauge at all. The gauge worked when I touched the negative cord of the starter.

I hope I have explained this so you can understand this. Anyway, I who know precious little about electrical wiring and am now really stumped. The elctricians I have spoken too seem to knowa lot about AC electrical problems and virtually nothing about D.C. Hookups. I would really appreciate some correct help on locating which of those four white wires is the correct one tocomplete this circuit so I can have a 12 volt receptacle in my galley.

thanks to youin advance,

Gene S.
gene so
Teardrop Advisor
Posts: 78
Joined: Sun Aug 21, 2011 9:47 pm
Location: las vegas, new mexico

Re: Help to complete a 12 v circuit

Postby tony.latham » Sun Mar 11, 2018 8:04 pm


This is where you lost me:

I attached the volt meter red line and also my existing black wire for the receptacle, to the "hot" cable of the electric starter.

What's the purpose of the electrical starter? Is that an engine starter?

It sounds like you know which wire is your positive 12V DC––your black wire, right? I think you are looking for a 12V ground wire, correct? If so, I'd unhook all the power (battery and 120V and test each white wire for continuity with your voltmeter to a known 12V ground.


Still scratching my head over your "electrical starter".

User avatar
Gold Donating Member
Posts: 3089
Images: 17
Joined: Mon Jul 08, 2013 4:03 pm
Location: Middle of Idaho on the edge of nowhere

Re: Help to complete a 12 v circuit

Postby Pinstriper » Sun Mar 11, 2018 8:28 pm

I am also having trouble understanding what is being described.

I *hope* we're not reading that you are mixing the AC and DC wiring systems. They have NOTHING in common.

Ooops, bad word, as "common" means something in AC wiring.
Let's eat, Grandma !
Let's eat Grandma !
Commas. They save lives.
User avatar
Teardrop Master
Posts: 109
Joined: Tue May 16, 2017 3:40 pm
Location: Outer SW Portlandia

Re: Help to complete a 12 v circuit

Postby pchast » Sun Mar 11, 2018 8:40 pm

Please don't tell me you forgot to mark every wire both ends..............
Are the connections still visible? :thinking:

If so and if the battery end is disconnected, you can test for wire
continuity and find out. ONLY IF nothing is hooked up to a battery
OR AC power. ..........
Platinum Donating Member
Posts: 1462
Images: 96
Joined: Mon Jan 28, 2013 5:47 pm
Location: Athens, NY

Re: Help to complete a 12 v circuit

Postby linuxmanxxx » Mon Mar 12, 2018 8:34 am

I think you'd be better off if you can access both ends just checking ohm resistance.

Sent from my Pixel 2 XL using Tapatalk
User avatar
500 Club
Posts: 733
Images: 10
Joined: Fri Sep 10, 2010 1:50 am
Location: Abilene TX

Re: Help to complete a 12 v circuit

Postby MtnDon » Mon Mar 12, 2018 9:39 am

I interpret "12v electric starter" to be one of those portable jump start boxes being used as a power supply.

It is difficult to envision how the wires are run, how they are being connected. Possibly the best method would be to use a multimeter and check the continuity of the individual wires. Is the mentioned voltmeter only a voltmeter or is it a multimeter? A multimeter has an "ohm" or resistance setting. That setting allows one to test that end A and end B have a complete circuit wire between them. With a multimeter used like that, you can eventually sort out all the wires when the ends are accessible and the wire length in between is hidden. You would probably need a longer wire with alligator clips on each end to help complete the test circuits, unless the multimeter has very long leads and the overall distances are relatively short. After all, TD's are not all that big.

So, the big question is do you have a multimeter? If not you can find them for under $10 in many places. Try a Harbor Freight, Autozone, Walmart....

Our 6x12 deep vee nose cargo trailer camper conversion... viewtopic.php?f=42&t=58336

We have a small off grid cabin we built ourselves in the NM mountains; small PV solar system; 624 watts PV, Outback CC & inverter/charger ...
User avatar
2000 Club
2000 Club
Posts: 2019
Images: 24
Joined: Sun Aug 19, 2012 10:57 pm
Location: New Mexico

Return to Electrical Secrets

Who is online

Users browsing this forum: No registered users and 2 guests