runs good, except with lights on

Discussion in 'GM Electrical Tech' started by gord19, Dec 13, 2013.

  1. gord19

    gord19 New Member

    i have a 1994 chev with a 305.
    it starts and runs fine but turn on the lights and it starts to run "rough", turn them off, runs fine.
    if i turn on the emergency flashers it will "miss" every time they flash.
    Then if i step on the brakes it will completely die.

    any ideas what could be wrong?
  2. Pikey

    Pikey Moderator Staff Member 5+ Years ROTM Winner 5000 Posts

    Sounds like a charging system issue. I had a 2003 yukon xl with a bad battery and alternator. When I would stop at a light it would almost stall. Let my foot off the brake and it was fine. I installed a new battery and alternator and it corrected the issue.
  3. Enkeiavalanche

    Enkeiavalanche Loving the Outdoors Staff Member 5+ Years ROTM Winner 5000 Posts

    Get them tested If you don't have what is needed go to a pep boys
  4. RayVoy

    RayVoy Epic Member 5+ Years 5000 Posts

    I agree with the guys, that it sounds like a battery that won't hold a charge, or an alternator that won't charge the battery. But, the lights don't use a lot of power and it seems you are using so much of the available power that there isn't enough remaining to keep the plugs firing. A battery needs to be pretty low before that becomes a problem.

    How does it start, does the battery spin the starter with sufficient power?

    I agree with the guys you need to have the battery and alternator tested, but you may need to check/clean/replace some of the ground cables.
  5. gord19

    gord19 New Member

    Replaced alternator today and Battery is new within the last 3 months.
    issues remain the same.
    starts and runs but turn on lights on touch brakes then dies, but will restart right away.

    Am i going to be chasing a bare wire somewhere in the harness?
    Last edited: Dec 14, 2013
  6. csltrains96

    csltrains96 Rockstar 100 Posts

    Just because the battery is fairly new, doesn't mean it can't have an issue. I'm with the rest of the guys. Have it tested. Then start looking for a short somewhere that is dragging both the battery and alternator down when you turn on the lights.
  7. RayVoy

    RayVoy Epic Member 5+ Years 5000 Posts

    Nothing wrong with getting the battery tested, it's a good place to have started, but a quick backyard check is to answer my previous question.
    If it spins the engine (no dragging and slowing down) the battery is probably fine. And if the battery is fine, the old alt was working because it kept the battery charged.

    As I suggested in my earlier post, you probably have a bad ground wire, or a bad ground connection.


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