Unit not charging; new battery installed; bulb tested with another battery...working fine. No light when charging; flickers with movement??????

Dull or Dim Brake Light Repair: If your car has a dull or dim brake light it is dangerous to you and other drivers. A dim brake light is a mystery to most people because the bulb is working, just not correctly. First confirm a new and correct brake light bulb has been installed. Next, turn the ignition key to the "on" position and have a helper depress the brake pedal. With the bulb installed touch a grounded test light to the outer bulb holder ring. If the bulb brightness changes the bulb socket ground has high resistance and needs to be repaired or replaced.

Flickering Brake Light Bulb Repair: A flickering brake light bulb can be very distracting and annoying. A brake light flickers because the power or ground is being obstructed momentarily. The most common cause for this condition is a loose fitting bulb socket. To check for this condition remove the brake light bulb in question, while a helper hold their foot on the brake pedal move the bulb around slightly in the socket. If the bulb flickers replace or repair the bulb socket as needed to regain proper brake light bulb operation. If the brake light bulb socket tests ok wiggle the brake light fuse and wiring at the brake light bulb socket, brake light switch and turn signal switch (American cars). If the brake light bulb flickers repair the component or wiring as needed.
Preferred Procedure: Always replace brake light bulbs with manufacturers recommend replacement bulbs. If you cannot find the correct replacement bulb part number consult an auto parts store for additional manufacturer information.
Common Problems
When brake light bulbs are replaced with the incorrect bulb causing no or dim brake light operation
If the brake lights stay on continuously it could mean the brake light switch has failed or an adjustment is needed.