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Dash lights only work when brights are on..

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Old Dec 3, 2012 | 11:03 PM
  #1  
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Dash lights only work when brights are on..

Can't find another thread with this situation detailed but Im almost certain I had this same problem in my early bronco several years ago.
All gauge lights come on when I hit the floor mounted dimmer switch to turn the brights on. If I hit it again to go back to lo beams, all the gauge lights go out.
Almost like the dash lights are grounded when I hit the dimmer switch and lose the ground on low beams...
Anybody have experience with this?

78 F250 Supercab
 
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Old Dec 4, 2012 | 07:36 AM
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That doesn't make sense (but not saying you aren't experiencing it) because the instrument lighting doesn't pick up from the high beams. My guess would be that something is bad in the light switch, since that is the only place that the headlights and dash lights meet.

Hopefully somebody with even more electrical knowledge will chime in. This is a curious problem
 
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Old Dec 4, 2012 | 09:15 AM
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There has to be some short somewhere, or a "present" left behind by a previous owner. The dash lights and dimmer switch are completely independent of one another.
 
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Old Dec 4, 2012 | 09:25 AM
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I'm not sure about the 77.5+ but do you have a "brights on" indicator light on the dash? The ground could be around that light circuit providing power to the rest of the dash when it is lit.
 
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Old Dec 4, 2012 | 09:47 AM
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Good point - however this thing has had so much rewiring done there is no telling what could be spliced incorrectly.
I'll keep digging.
 
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Old Dec 4, 2012 | 10:29 AM
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Originally Posted by Jimmyrig
I'm not sure about the 77.5+ but do you have a "brights on" indicator light on the dash? The ground could be around that light circuit providing power to the rest of the dash when it is lit.

Yes - I do have a bright light on indicator that does come on with the gauge lights when I step on the button.

Good place to start.
 
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