Dusting off an old device and bringing up openwrt-18.06 at ae2a3a1 (2018-10-09) on it, it seems to work like a champ, but I'm not seeing a device or LuCI entry for the 5G LED.
There is not a entry for a 5G LED in
target/linux/ar71xx/files/arch/mips/ath79/mach-tl-wdr4300.c
target/linux/ar71xx/base-files/etc/board.d/01_leds
Anyone have a recollection of this?
jeff@Home:/$ ls /sys/class/leds/
ath9k-phy0 tp-link:blue:lan1 tp-link:blue:lan3 tp-link:blue:qss tp-link:blue:wan tp-link:green:usb1
ath9k-phy1 tp-link:blue:lan2 tp-link:blue:lan4 tp-link:blue:system tp-link:blue:wlan2g tp-link:green:usb2
Edit:
https://openwrt.org/toh/tp-link/tl-wdr4300
The 5GHz LED seems not to be controlled via GPIO.