12 grille lights use 2.5 square lines. Why is the wire heated?
See how the wiring, line type selection, whether the standard, hard wire, wire diameter?.Normally, a control circuit is not connected to 12 lamps, especially fluorescent lamps.
Load power is too large (2.5 square copper wire rated current is 20 amperes, tube through, temperature 8,9 fold)
The lead joint is not strong and the resistance is too large. Tin is recommended
