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Why does my odometer flicker all numbers and get dim when I sometimes hit the brakes. Nothing else in the dash is affected except the radio and it's only sometimes. Is there a short behind the radio

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  • Welcome to SE Mechanics! This is a good question, but hard to answer without more information. It would help to know how old the car is and if it is the original radio. Also, is this a new problem? If it is can you tell us about when it started and if there is anything that could correlate with it?
    – dlu
    Jul 30 '16 at 18:07
  • What do you notice in the radio?
    – dlu
    Jul 30 '16 at 18:21
  • Even if it isn't obviously relevant, it would not hurt to add the model and year of your car.
    – dlu
    Jul 30 '16 at 18:33
  • How can this be answered without Make Model and Year of Vehicle??
    – Moab
    Jul 31 '16 at 21:40
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There are two possibilities that come to mind:

  1. Hitting the brakes turns on the brake lights, so there might be an issue with grounds or a loose wire that could be causing other circuits to appear to loose power.

  2. Hitting the brakes also invokes Newton's 1st law (roughly speaking, when you change the forces on things (apply the brakes), they can move) perhaps the radio (why are you suspicious of it?) or its wiring harness are moving and damage to the wires when the radio was installed are causing the flickering.

Neither are simple problems to track down. But you may be able to at least get pointed in the right direction by noting when it happens:

  • If the problem is due to the brake lights going on it will happen even if the car is not moving and it won't matter how hard you push on the brake pedal. All that matters is that the brake switch get's activated.

  • On the other hand if the problem is due to something shifting when the brakes are applied the problem will likely not occur when the brakes are applied while stopped and will be more likely to occur if the brakes are applied hard.

So you might find a safe place to do some experimentation. What you'd like to come up with is a way to reproduce the problem. If you get to the point where you can make it occur pretty reliably and you're still not sure of the cause another thing you could try would be to find and disconnect the brake light switch (it is usually somewhere near the brake pedal). If the problem is related to the brake lights going on disconnecting the switch should make it go away. Be sure to reconnect the switch before driving on the road.

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Check all the fuses; perhaps there is a bit of corrosion, etc. How old is the Chevy? On older cars corrosion on fuses with the old tubular style fuses was common. The brake lights draw a fair amount of current, and if the fuses are corroded, it could affect anything else on the circuit.

Image cropped from https://commons.wikimedia.org/wiki/File%3ASelection_of_Fuses.JPG

enter image description here

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  • I am curious how this answers an intermittent issue with the odometer and the radio when the brake pedal is pressed. Can you explain your answer a little better?
    – CharlieRB
    Aug 29 '16 at 20:56
  • The brake lights draw a fair amount of current, and if the fuses are corroded, it could affect anything else on the circuit. Aug 29 '16 at 22:00
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    That makes more sense. Can you add that to your answer?
    – CharlieRB
    Aug 30 '16 at 12:17

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