I am refurbishing a 1988 TT and cannot figure out what is wrong with the 12v lights. I checked the battery, and it is fine. I ran a long jumper wire from the ground on the battery to my test light and I have power at the socket in the 12v light, but the bulb will not come on in any of the 12v fixtures. I even tried a new bulb to be sure, but nothing. This has me thinking I have a ground problem, but, then again, the water pump functions normally. There is only one ground wire hooked to the battery, so it has to be the same ground feeding the lights, right? Also, when I touch the test light to either the end of the bulb in the fixture, or the side casing, my test light comes on. I thought the side casing of the bulb is for the ground, but I'm not sure. Any suggestions?
12V interior lighting problems
- Thread starter ALAG3
- Start date
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Frank B
Well-known member
OK, I don't quite follow that. You have power on the lead that touches the pin on the end of the bulb? Again, if you touch the the outer casing of the bulb with your test light, you get a reading? Where do you have the other end of your test light connected when you do this? If it is to a ground point in the trailer, then you do have a bad ground at the light socket. Your test light will sense power going into the bulb, across the filament, and out to the casing on the bulb. You will only get this if the ground on the light socket is bad.
Frank.
Frank.
John From Detroit
Well-known member
Let me see if I get it
You ran a long jumper wire from the battery to the light socket and you have power to the socket
But the light does not light
That kind of leaves you with two and only two choioces
1, Bad socket.. To test for bad socket the easy way, take your test lamp, touch the power lead on the socket side of the switch, light lights. good, you have 12 v to the bulb
Now touch the SHELL of the socket (or the ground lead) Lights (either test lamp, fixture lamp or both) come on.. BAD GROUND ELSE bad socket or bad bulb.
if socket or bulb is bad, YOu can test by moving the jumper lead to the positive (or just test across the socket with the test lamp
I'm goning to take a wild guess and suspect the grounds first, and the socket 2nd.
You ran a long jumper wire from the battery to the light socket and you have power to the socket
But the light does not light
That kind of leaves you with two and only two choioces
1, Bad socket.. To test for bad socket the easy way, take your test lamp, touch the power lead on the socket side of the switch, light lights. good, you have 12 v to the bulb
Now touch the SHELL of the socket (or the ground lead) Lights (either test lamp, fixture lamp or both) come on.. BAD GROUND ELSE bad socket or bad bulb.
if socket or bulb is bad, YOu can test by moving the jumper lead to the positive (or just test across the socket with the test lamp
I'm goning to take a wild guess and suspect the grounds first, and the socket 2nd.
Karl
Moderator Emeritus
Don't assume that the ground is good. The water pump will almost surely have its' own ground wire attached somewhere on the frame, and the interior lights probably have their own ground(s) attached to the frame somewhere else. On 'vintage' rigs such as yours, it's not uncommon for the bulb sockets to become corroded. Disconnect the negative terminal at the battery and one by one, remove the bulbs and clean the inside contacts of both the bulb and socket with a brass brush or fine sandpaper. If that doesn't work, try taking a length of wire and connect one end of it to the metal base of the bulb and connect the other end to a clean spot on the frame. If it lights, you have a bad ground and need to trace it out and fix it. If it still doesn't light, measure for 12VDC the center connector of the bulb. If it's not there, you may have a blown fuse for the lighting circuit.
Good luck!
Good luck!
I finally found the problem. The ground wires are connected in near the converter and whoever owned it before me had them taped with electrical tape to the main ground for the trailer. The main ground wire had come out of the electrical tape. I put them all back together with a wire nut and all is working fine. Thanks for the input!
Gary RV_Wizard
Site Team
Glad you found it. Bad grounds can be pesky.
Carl L
Moderator Emeritus
ALAG3 said:
The presence of electrical tape is almost a sure sign of someone's poor efforts at wiring. Good DC wiring practice uses heat shrink insulation and, in addition, soldering on any connection exposed to weather or moisture.
I gained this experience completely rehabbing a junky wiring job on an used boat I owned a few years back.
Hfx_Cdn
Well-known member
Whiole on the subject of poor grounding, I had a problem with the 12V light fixture over the table on our coach. Tried for about 3 days to track it down, as most 12V problems are poor ground connections, but I couldn't find a thing. I gave up, and about a week later I had to retrieve something the grandkids dropped behing the hide-a-bed, and when I hit the white wire, the light came on. I followed the wire and found one of those "in line" splices on the ground, and it had severed the wire, so when you talk about cheap short cuts, thats what caused it, soldered the connection, and it works like a charm 
John From Detroit
Well-known member
I see my "Wild Guess" that one should suspect the grounds first was not so wild after all
(Actually, it's badsed upon experience,, Grounds are the #1 problem in the 12V electrical system) That is because most other connections are like to like (metal wise) but grounds are often like to unlike.. Your specific problem is.. Not exactly as common as just bad bround... However bad connections in general.. That's #2
(Actually, it's badsed upon experience,, Grounds are the #1 problem in the 12V electrical system) That is because most other connections are like to like (metal wise) but grounds are often like to unlike.. Your specific problem is.. Not exactly as common as just bad bround... However bad connections in general.. That's #2
