Testing electrical 1990 Suburban

Discussion in 'Chevy Suburban Forum (GMC Yukon XL)' started by Bogel, Feb 13, 2014.

  1. Bogel

    Bogel New Member

    I was hoping to get a little advice on testing some electrical pieces on my suburban. Its a 3/4 ton 350TBI TH400 ect...

    Basically 2 problems.

    #1 Running lights drivers side rear are not functioning.

    Brake lights turning signals work, just no running lights on the drivers side rear only.

    I did a little bit of research on this, and my reading points to a faulty light socket. I have a volt meter, was hoping there is a way I could test this before I order a new socket. I have tried the bulb from the passenger side which is working, no change.

    #2 Fuel gauge is crazy.

    It works sometimes, most of the time it doesn't. I suspect ground due to wacky nature and the fact that it does work.

    I suspect this is the ground wire or gauges, waiting for it warm up outside before I go test.

    Just looking for a little advice to see if I am heading in the right direction.
  2. Pikey

    Pikey Moderator Staff Member 5+ Years ROTM Winner 5000 Posts

    your fuel gauge could be a bad sending unit. As far as testing to see if the socket is bad. Since I do not have a wiring schematic for that vehicle I would start by turning on the running lights. We know that the passenger side works. So, I would go to the passenger side and probe the wires at the socket with a test light. Looking for power. Then I would go probe the other side. If it is the socket then you should have power going to the exact same wires on both sides. Lets say you have power on the passenger side on a orange wire (just an arbitrary color I came up with) and you test the driver side and find that the same orange wire in that side does not have power, then you have a wiring issue rather than a bad socket.
  3. Bogel

    Bogel New Member

    Thanks for clearing that up for me there, I am not the best with electrical.

    I should be able to get out to work on the truck Tuesday sometime.
  4. RayVoy

    RayVoy Epic Member 5+ Years 5000 Posts

    By any chance, did we try new bulbs in both locations (I know you did in one)?

    That is by far the most common reason for a light to stop working.
  5. Bogel

    Bogel New Member

    I did not, I tried the working bulb in the side that was not working, no change. I also tested the non-working bulb in the working side, worked perfectly.

    I should however replace them with new ones just to be safe.
  6. RayVoy

    RayVoy Epic Member 5+ Years 5000 Posts

    Well, hang on, I think you did a reasonable check, it does appear to be something other than the bulbs.
  7. Jamm3r

    Jamm3r Member 2 Years 100 Posts

    It is extremely common for these to fail. I've tried fixing them and can't. Best to replace the whole assembly on both sides

    Usually a bad ground on the fuel pump/fuel tank assembly
  8. Bogel

    Bogel New Member

    I did the test, I have a new light socket in the mail, I may replace the other one in the future. I will probably be dropping the tank for other issues here in the next few weeks after I test the fuel pressure. Thanks for the help, will post back whenever I get the socket socket changed.

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