12 volt problems?

Discussion in 'General RVing' started by brandon, Jul 20, 2005.

  1. brandon

    brandon New Member

    I am having trouble with the 12 volt system in my 1977 gmc tioga. All interior lights work when th vehicle is running or plugged in to 120, but problem when trying to use battery. What happens is when I turn on an interior light the rear parking lights come on and the interior light is very dim. Also, if I turn on two interior lights they both fail. Also, not enough 12 volt power to run water pump. This was not a problem last season but after a short trip this year, it started. I think it may be a ground problem but where do I start looking. Any help would be greatly appreciated. thanks
     
  2. hertig

    hertig Senior Member

    12 volt problems?

    Since everything works on 120 volts, the problem would seem to be with the batteries. Generally there will be a 'converter' which provides 12v from 120v, and also charges the batteries. This seems to be working from your description.

    Check to be sure the batteries are hooked up correctly. If so, then I'd disconnect the batteries from the trailer and hook them to a battery tester. If they are in good shape, then it gets much more tricky.

    Electrical problems can be tough to find. The first thing I'd do is remove all the 12 volt fuses, then put in one fuse and try everything on that circuit. Then remove that fuse and put in the next, repeat until you have a 'chart' of everything which does work and does not work. Hopefully, only one circuit will be bad. If nothing works, then the problem is probably between the fuse panel and the batteries.

    I might as a last resort disconnect the converter on the off chance it was something in the output stage of that.
     
  3. TexasClodhopper

    TexasClodhopper Senior Member

    12 volt problems?

    brandon, you sure seem to have a grounding problem. The current is going through a lamp filament instead of to ground. That could mean that a ground has "lifted" at a lamp or it could be a major ground wire. I suspect the latter since more than one object is involved. Look for an area in your MH where all the ground wires come together. Probably near the house batteries. Be sure and check around the pump, too. It vibrates a lot, so it may have come loose there. Good luck.
     
  4. brandon

    brandon New Member

    12 volt problems?

    thanks guys, I'll try both
     
  5. brandon

    brandon New Member

    12 volt problems?

    In my last post about a 12 volt problem,I may have left out one key issue. The 8 track radio from the dash has be removed and their are now free wires under dash. (One red with a live current and two black which I think are grounds). Could the loose wires be the cause of my problems, if so what should I do with them. thanks
     
  6. brandon

    brandon New Member

    12 volt problems?

    In my last post about a 12 volt problem,I may have left out one key issue. The 8 track radio from the dash has be removed and their are now free wires under dash. (One red with a live current and two black which I think are grounds). Could the loose wires be the cause of my problems, if so what should I do with them. thanks
     
  7. Kirk

    Kirk Senior Member

    12 volt problems?

    As a former tech., I would say that Texas Clodhopper was on the right track. The fact that lights come on is a hint, as is the fact that everything seems to work until you attempt to use the battery. In reading all of your posts, I think that you very likely have at least two different problems, but it is difficult to be sure. To trouble shoot you really need to have a meter, preferable one of the digital variety in the $30 or so price range.

    The first thing that I would do is to tape off the leads at the dash to make sure that they are not shorting, even though they probably have no connection to the issue. The 8 track probably got power from the chassis while your basic problem seems to be with the coach. When properly wired and the engin off, there should be no connection to the lights of the chassis. Have you checked to be sure that the tail lights do not turn on when you use the lights from shore power? If the battery is a little weak, it may be that the lights are on, but you just never noticed because the greater power source works well and you have never looked!

    Another thing that I would do is to remove the coach battery from the circuit and charge it fully and then allow it to sit for a few days to see if it can maintain the charged condition. It sounds to me as though your battery is not charging properly. Have you checked to make sure that the electrolite is where it should be?

    For the tail lights to be lighting, there has to be some connection between the chassis electrical system and the one for the coach. Try lifting the negitive cable from your chassis battery and see if anything changes. Both batteries do use the chassis of the RV as a return path so you need to seperate the two first. I wonder if the battery isolator is opeing like it should? Check to see if it has seperated the two electrical systems? If it has not, that could be why the tail lights are lighting.

    You can find some good information by checking the voltage that you have from each of the three different power sources. Use a meter and read at any 12V power plug, or at any light or power connection. It would be a good idea to also check the voltage at the 12V output of the converter when on shore power and at the coach battery posts with the engine running, when on shore power and when on the battery. The shore power or the chassis alternator should supply power to the coach battery and voltage checks will tell you if they are.

    From the coach battery, measure from the negitive post to some good electrical contact point on the RV frame. That resistance should be less than 1 ohm, and never over 10 ohms. If it is, solve that problem first. Loss of ground is a very common problem on older RVs.
     

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