[Richard L]

This problem has mde easier for me as you have given me some clues.

If the gauge goes dim, it is due to the main power supply into the system, ie, the red wire from the 4-way power plug. As the yellow led's supply is regulated to 5V internally it will not be affected by a noisy 12V supply.

Is it possible to find another loaction for the red wire (molex)? It can be connected directly to the battery. The system's will not drain power until the ignition swicth is at the "run" position.