Re:P 38 COCKPIT DETAILS
The Pilot's Flight Operating Instructions for Army Models P-38H Series, P-38J Series, P-38L-1, L-5 & F-5B Airplanes ISBN # 0-87994-0 shows what surely is the same instrument but lower on the panel. It is the turbo Warning instrument with a left light, right light and a third button(?) labeled "Push to Test". In other instrument panel layouts this area is either blank or has a warning label of some sort.