1986 Isuzu Impulse no power

When I push the A/C button in there is no response from the A/C.
Also when I slide the fan lever, no fan kicks in.
I know it is an electrical supply issue so the fuse I checked and ichanged with new.
I am now going to change the relay but I have a feeling it is not the relay.
Where else can I troubleshoot this problem.
The light on the push button does not come on at all it has to be power supply problem but from where is is cut off?