150 Speedo

There is a brighter bulb for use in the 4 for illumination . SlantSixDan can provide the number. I didn't write it down but I did purchase for my panel.
Providing a sufficient ground is crucial for any though. Pot metal is not a optimal conductor then chrome plated screws in black oxide coated U nuts placed on painted steel all adds up to measurable resistance. Add a ground wire on both printed circuit boards. Might be all you need and surely less expensive than 4 dollar per bulb(s).