4H was working fine now when I press the 4WD button light on dash does not illuminate and definitely isn’t in 4WD. L4 does work though as you don’t need button for that just shift the gear.
Any ideas on where to start looking to fix this
Probably easier if you google hilux ADD or look on newhilux.net.
As mentioned you will see the wires connected to it on the front diff. It's a known failure usually from water getting in. I think Toyota only sell them complete but some have been able to clean them up or fit a new motor