JL 500/5 low ohm light 2 seconds upon turn on

Just purchased a used jl 500/5 . Was told working all well.
Brought it home did a power test no speakers hooked up to it .would turn on but the low ohm light would aluminate for approx 2 seconds then fade away green power light afterwa5ds, I tested each channel with a 4 ohm bookshelf speaker. All channels work well gain works,channels clear sounds equal loudness . When amp powers down low ohm light turns on right at the end ?

Also I removed the cover and powered up, all green leds come on at same time same speed .same brightness.

I called jl audio tech no real information gained .amp was too old for accurate knowledge. He was leaning towards internal short.