Help, I'm baffled! Interior lighting circuit reading at 6V instead of 12V!

[sailbound]

While attempting to wire two small (1 watt) red LED courtesy lights off of a light switch in the bathroom of of our new 265BH, I noticed both lit very dimly and were clearly under-powered. I then checked with a volt meter and see that the circuit is reading a consistent 5.8 volts. This switch comes off the main overhead lighting circuit where the factory overhead LEDs are all at their usual brightness with no indications of low voltage or shorting. I'm not an electrical engineer, but I have had four different sailboats over the years and am fairly good at basic stuff like this. Some jokes here may be warranted, but I am completely baffled as to why this is happening and hoping someone can help me resolve it!

[Country Campers]

While attempting to wire two small (1 watt) red LED courtesy lights off of a light switch in the bathroom of of our new 265BH, I noticed both lit very dimly and were clearly under-powered. I then checked with a volt meter and see that the circuit is reading a consistent 5.8 volts. This switch comes off the main overhead lighting circuit where the factory overhead LEDs are all at their usual brightness with no indications of low voltage or shorting. I'm not an electrical engineer, but I have had four different sailboats over the years and am fairly good at basic stuff like this. Some jokes here may be warranted, but I am completely baffled as to why this is happening and hoping someone can help me resolve it!

Welcome aboard , get it , haha.

Have you tried to test the light on another circuit? Any way to test it off of another battery or source.
If all of the lights work on the circuit and this new light does not I can only guess that the new light is bad. Another thought is to make sure you are connecting to the right wires , + to + , - to -.

Brian

[howson]

While attempting to wire two small (1 watt) red LED courtesy lights off of a light switch in the bathroom of of our new 265BH, I noticed both lit very dimly and were clearly under-powered. I then checked with a volt meter and see that the circuit is reading a consistent 5.8 volts. This switch comes off the main overhead lighting circuit where the factory overhead LEDs are all at their usual brightness with no indications of low voltage or shorting. I'm not an electrical engineer, but I have had four different sailboats over the years and am fairly good at basic stuff like this. Some jokes here may be warranted, but I am completely baffled as to why this is happening and hoping someone can help me resolve it!

Ahoy there, sailbound! (I had to copy Brian...)

Sounds like you wired the new light in series with the camper's OEM lights. The OEM lights seemingly working normally works against that diagnosis, though.

The other possibility is the new LEDs are wired backwards as Brian suggested. In GD's OEM wiring the solid white wire is the negative, or ground. The hot wire is normally some color, even if it's just a stripe on a white wire.

[Jkwilson]

A switch will seldom have both sides of the power source available. Likely switching just the 12V line with no negative available.

[sailbound]

Thank you all for your responses... thought I'd be notified of responses, but that didn't happen so I just realized there were answers here - thank you! For clarity, the trailer is wired with the main switch for all overhead lights at the main entry and then the Bathroom and Master bedroom lights controlled by additional switches off that main circuit.

Again, I am attempting to tap the power at the Bathroom switch and noticed that rather than typical Red/Black wire coming in, there are actually two Red (combined in single spade connector) and a single Brown wire. Testing tells me that one Red is the incoming power to the Bathroom switch, and the additional Red wire then carries power on to the Master Bedroom. I have searched with mixed results on what the Brown wire is... some say positive, some negative for DC circuits - perhaps this is where the problem lies.

The one thing I can say with certainty is that multi-meter testing (Red on Red and Black on Brown) is giving me the 5.8V reading, one that seems to be confirmed with TWO separate LED lights that are both underpowered when wired this way... I doubt the LEDs and meter are all wrong. BUT.... now wondering if I'm making incorrect assumptions that Brown is negative in this case?? More than willing to admit I'm not as good as I thought, and will do so immediately if someone can help me solve this! Just don't tell my wife.

[howson]

Thank you all for your responses... thought I'd be notified of responses, but that didn't happen so I just realized there were answers here - thank you! For clarity, the trailer is wired with the main switch for all overhead lights at the main entry and then the Bathroom and Master bedroom lights controlled by additional switches off that main circuit.

???

Are you saying the bathroom and bedroom lights in your RV won't work if the "main switch for all overhead lights at the main entry" isn't on?

[Country Campers]

Thank you all for your responses... thought I'd be notified of responses, but that didn't happen so I just realized there were answers here - thank you! For clarity, the trailer is wired with the main switch for all overhead lights at the main entry and then the Bathroom and Master bedroom lights controlled by additional switches off that main circuit.

Again, I am attempting to tap the power at the Bathroom switch and noticed that rather than typical Red/Black wire coming in, there are actually two Red (combined in single spade connector) and a single Brown wire. Testing tells me that one Red is the incoming power to the Bathroom switch, and the additional Red wire then carries power on to the Master Bedroom. I have searched with mixed results on what the Brown wire is... some say positive, some negative for DC circuits - perhaps this is where the problem lies.

The one thing I can say with certainty is that multi-meter testing (Red on Red and Black on Brown) is giving me the 5.8V reading, one that seems to be confirmed with TWO separate LED lights that are both underpowered when wired this way... I doubt the LEDs and meter are all wrong. BUT.... now wondering if I'm making incorrect assumptions that Brown is negative in this case?? More than willing to admit I'm not as good as I thought, and will do so immediately if someone can help me solve this! Just don't tell my wife.

To determine which wire is which.....

If you have a long piece of wire that you can attach to a known ground , on the battery or at the power panel , that will reach to the switch that you have in question then you can use that to check for power on the wires as well as which wire is ground. You can also use this to see that you have zero resistance to the ground wire and if there is a short to ground on that switch or circuit.

I will check your settings to see if you have them set up to receive notifications if you wish. When you select to receive notifications you should get an email that alerts you to a quote or tag.

Brian

[Cate&Rob]

sailbound

Welcome to our forum BTW . . . I am just catching up to this thread . . . we have been travelling.
Another long time boater here . . . but, mostly power.

As noted above, you will not likely have a ground wire at the switch location. The RV convention for ground wires is white. Any other color can be +12V. Where this gets even more confusing is that prewired devices like lights often use the conventional black -ve and red +ve. So, the brown wire is likely bringing 12V to the switch and the red wires are likely taking this 12V to the lights.

The confusing part is that you have to have the main light switch turned on for this other switch to work. This is not normal. My guess is that one circuit is being grounded through another light which has enough resistance to drop the normal 12V to the lower voltage.

I would start by putting your meter between the disconnected brown wire (+ve) and the panel ground plate (-ve). This should show 12V and should be unaffected by turning the main light switch on/off. If this is correct, you are going to have to figure out where the -ve wire from the lights is grounded. These wires are probably black and paired with the two red wires at the switch. These black wires should go to a white wire which will be the RV ground circuit.

If you can post pictures of what you are working with, this will help us to help you.

Rob

[sailbound]

All, please forgive my tardy reply here, but this whole effort was in prep for a long-planned family RV trip to Florida over the past two weeks... while we unfortunately had to cancel due to the pandemic, I still took the time off which --most importantly-- includes ignoring my phone and PC as much as possible. My wife likes this, but I feel like I've been a bad forum friend.

Thanks again to all for your responses. I was able to solve the problem, with special thanks to the post from Cate&Rob here - your description addressed my problem perfectly - very helpful, thank you! I was wrong about the overhead lights switch at the entry acting as a main switch for lighting in bath and bedroom - this was a miscommunication between my wife and I. The rooms are powered independently, and I was able to easily source and tap a white (-) wire running down the wall to solve my issue. I now have red courtesy lights in both living area and bath, and I learned a lot about how things are wired in the process!

While not critically important, I'm still baffled why the LEDs lit up at all when connected to two positive (red and brown) wires. I always thought 12V required both positive and negative were required to complete a circuit but maybe have more to learn here too?

Anyway, again, I am incredibly grateful for the quick and friendly help here and glad to be part of the forum. Given that DIY improvements and tinkering with things in general is half the fun for me, I'm sure I'll be posting more here soon when I get into my next "oh sh*t" moment. I will also try to be more brief in the future... think I just feel guilty for disappearing for awhile!

Many thanks and hope to see you all out there soon when the gets back to normal! Until then, please stay healthy and safe!

[Cate&Rob]

I'm still baffled why the LEDs lit up at all when connected to two positive (red and brown) wires. I always thought 12V required both positive and negative were required to complete a circuit

Hi sailbound,

Welcome back . . . I was wondering where you went .
Sorry to learn that your RV trip got cancelled . . . many (most?) of us are in the same/similar situation. For us, we had to come back to Canada early from our winter in Florida.

WRT your question . . . a light (even an LED) just needs to see a voltage difference between one wire and the other, to light the bulb. So, the brown wire would be at 12V and the red wire would be at a lower voltage through the resistance of the other lights on the circuit to ground. Obviously enough voltage difference to turn on the LED.

When you join us on a more regular basis, please fill out you signature block (to remind us which Grand Design rig you have) and if you don't mind, sign your posts so we get to a "first name" basis.

Thanks for the kind comments BTW. You will find that your years of boating experience will prepare you well for your new "land yacht".

Rob

[sailbound]

Cate&Rob , once again, thanks for your reply. The voltage diff activating the light makes sense but certainly added to the confusion on my project. My signature is also now now updated and active. My name is David, wife is Nanette, and we have two preteens - sorry for leaving my name out as I usually do sign off with it. I'm a lifelong Californian who just moved from Santa Barbara to Louisville, KY... and, yes, between culture change and being landlocked, there is definitely an adjustment in making this move! Still at least on the Ohio River which helps!.

Yes, I quickly grasped the systems and maintenance on the RV, so now it's just a matter of keeping a good maintenance checklist and departure routine while also improving my backing skills. My sailboat was 52' so couldn't be towed, and a 33' trailer is a good bit bigger than the 18' ski boat I towed many years ago. My one crazy habit that needs breaking is thinking that everything in the RV needs to be secured when camping. I'm used to things heeling over a good 30-45 degrees when underway... hopefully, this is never the case!

Thanks again,
David

[Cate&Rob]

sailbound
Hi David & Nanette,

We are wandering way off topic here (which we are not supposed to do) but I have to follow this for a moment.
Many years on a 40 ft trawler and various smaller sailboats before that, so I can relate.
It is so nice waking up every morning on the RV to see that the anchor didn’t drag overnight .

Welcome to our new world!

Rob (& Cate)