12vdc bedroom lights dim even with switch off

Davenport · 11-23-2021, 11:13 AM

2016 Dynamax DX3. When I turn off the bedroom light switch, lights are still on very dim. Same with bathroom lights. I have checked switches, all working properly. I did find that even if I pull the fuse in buss lights still on very dim, but will not turn on all the way. I decided that maybe there was a back feed from another circuit so I pulled other fuses one at a time and I found it. The fuse to the "Fan/AC" (this runs both AC fans and the bathroom vent fan), when removed the lights in bedroom and bathroom went out, but still worked correctly by their own switch (on/off). That leads me to believe that the wiring for the fans is cross feeding into the light wiring. Problem is where to start tracing wires? I have no schematics for this and can't find anything showing how the wiring is run for this model coach. Lazy days in Murfreesboro, TN. have been helping but they are as lost as me.
Any help would be greatly appreciated,
Billy Davenport
Tennessee

groovezilla79 · 11-23-2021, 11:20 AM

May not be your case, but we had this happen once and it was the inverter doing some crazy stuff. Ended up replacing it and the issues went away. Not sure if that's been checked or not in your unit. Good luck.

SeaDog · 11-23-2021, 11:20 AM

welcome to the forum its a great place to get your questions answered. Sounds like something is wired backward and feeding thru. I think I would start at the lights and work my way backward until I found the circuit that removes the power. chasing electrical can be a drawn out process good luck

Davenport · 11-23-2021, 11:32 AM

groovezilla79: Thanks for the input. I just replaced the inverter because of other issues. Thought it might fix this problem to but, didn't get that lucky.

W5CRE · 11-23-2021, 11:43 AM

Inspect, tighten and clean all DC grounds you can find. Check rooftop dc devices for corrosion. These are a couple of frequent causes of electrical problems on trailers.

D W · 11-23-2021, 11:50 AM

Quote:

Originally Posted by W5CRE

Inspect, tighten and clean all DC grounds you can find. Check rooftop dc devices for corrosion. These are a couple of frequent causes of electrical problems on trailers.

X2. The deficiency described is very often a defective ground.

Davenport · 11-24-2021, 02:33 PM

Quote:

Originally Posted by D W

X2. The deficiency described is very often a defective ground.

Tried to find the ground terminal and I have been unable to locate it. My 12vdc buss bar/fuse terminal under the bed has a red hot wire supplying power to it but no ground. where would the ground terminal bus for the fuse terminal be?

llr · 11-24-2021, 02:54 PM

Quote:

Originally Posted by Davenport

Tried to find the ground terminal and I have been unable to locate it. My 12vdc buss bar/fuse terminal under the bed has a red hot wire supplying power to it but no ground. where would the ground terminal bus for the fuse terminal be?

They probably just attach to the nearest metal possible. My guess is they both attach to this metal and it is a connection between here and the battery.

It may be almost impossible to find, if you can run a new ground wire that would be easiest

PenJoe · 11-24-2021, 03:46 PM

Just curious, are the lights that stay on LED or incandescent? LED lights have a diode that prevents back feed.

Our son, an electrical engineer, just happens to be visiting with us and I asked him the question. We were in agreement that it could well be a grounding problem. If you have incandescent lights, changing to LEDs may solve the lights being totally off, but it would not solve the problem.

The problem may be that the two areas have what is called a floating ground that could be traced with a volt meter. You may have to do continuity testing as-well to isolate the problem. The two references may help explain the issue

https://www.bing.com/images/search?q...1&disoverlay=1

Just curious, are the lights that stay on LED or incandescent? LED lights have a diode that prevents back feed.

Our son, and electrical engineer, just happens to be visiting with us and I asked him the question. We were in agreement that it coul;d well be a grounding problem. If you have incandescent lights, changing to LEDs may solve the lights being totally off, but it would not solve the problem.

The problem may be that the two areas have what is called a floating ground that could be traced with a volt meter. You may have to do continuity testing as-well to isolate the problem. The two references may help explain the issue

https://www.bing.com/images/search?q...1&disoverlay=1

https://www.solaris-shop.com/blog/gr...verter-damage/

https://diysolarforum.com/threads/ho...-ground.11009/

PenJoe · 11-24-2021, 04:12 PM

Quote:

Originally Posted by Davenport

Tried to find the ground terminal and I have been unable to locate it. My 12vdc buss bar/fuse terminal under the bed has a red hot wire supplying power to it but no ground. where would the ground terminal bus for the fuse terminal be?

Unlike house wiring with a black/white/ground wire, RVs grounding is connected to the chassis. So, there is no ground wire at the buss under the bed. The grounding is to any metal that has a direct connection to the chassis. The inverter and the batteries must be grounded to the chassis. The neutral wire from any 12v light fixture or appliance must ultimately be connected to the chassis by any metal having contact with the chassis. The positive wire goes to fuse panel , then to the switch that operates the light fixture. That connects the circuits. If the switch is off and the lights are still on, there is back feed current.

Davenport · 11-24-2021, 05:01 PM

Thanks everyone for the input, it was very informative. Problem found. In the original post I talked about the vent fan on another circuit and when I pulled the fuse for it the lights went out, (LED's). Well the wiring to the fan "somewhere in the ceiling was feeding low voltage current to the light wiring. Cut the lead to the fan and ran new lead to it from fuse panel and problem solved. Hope this makes sense to you.
Thanks all for the input, I did learn a lot from reading your posts.

dave1650 · 11-24-2021, 05:37 PM

Quote:

Originally Posted by Davenport

Thanks everyone for the input, it was very informative. Problem found. In the original post I talked about the vent fan on another circuit and when I pulled the fuse for it the lights went out, (LED's). Well the wiring to the fan "somewhere in the ceiling was feeding low voltage current to the light wiring. Cut the lead to the fan and ran new lead to it from fuse panel and problem solved. Hope this makes sense to you.
Thanks all for the input, I did learn a lot from reading your posts.

That makes a lot better sense then the ground problems. It had to be leakage on the wire from the switch to the lights. That was a good way to eliminate a lot of time and hassle and is a good way to solve the problem. Happy camping.

aircommuter · 11-25-2021, 08:53 AM

[QUOTE=PenJoe;2664925]Just curious, are the lights that stay on LED or incandescent? LED lights have a diode that prevents back feed.

Our son, an electrical engineer, just happens to be visiting with us and I asked him the question. We were in agreement that it could well be a grounding problem. If you have incandescent lights, changing to LEDs may solve the lights being totally off, but it would not solve the problem.

The problem may be that the two areas have what is called a floating ground that could be traced with a volt meter. You may have to do continuity testing as-well to isolate the problem. The two references may help explain the issue

https://www.bing.com/images/search?q...1&disoverlay=1

Just curious, are the lights that stay on LED or incandescent? LED lights have a diode that prevents back feed.

Our son, and electrical engineer, just happens to be visiting with us and I asked him the question. We were in agreement that it coul;d well be a grounding problem. If you have incandescent lights, changing to LEDs may solve the lights being totally off, but it would not solve the problem.

The problem may be that the two areas have what is called a floating ground that could be traced with a volt meter. You may have to do continuity testing as-well to isolate the problem. The two references may help explain the issue

https://www.bing.com/images/search?q...1&disoverlay=1

https://www.solaris-shop.com/blog/gr...verter-damage/

https://diysolarforum.com/threads/ho...-ground.11009/[/QUOTE
LED is a diode.

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