Often the electrical contacts on the removable bulb holders get dirty or partially corroded, and then don't carry current well.
This can cause the Brake Lights or other Rear lights to fail intermittantly or fail completely.
1. Clean the contacts in the bulb holders and the contact areas on all the bulbs involved.
Use a small piece of emery cloth, or a piece of steel wool.
2. Check the connections where the wiring connects to the lights.
Clean away any corrosion and make sure the contacts are tight.
Sometimes you can use needle nose pliers to gently tighten them.
Replace any corroded wiring.
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