Hello I need some help.my 98 chevy pick up has no taillights ,my brake and turn signals work.I have checked my fuses all seem OK .What to look for now?

Have you physically inspected the bulb, I do believe on that year it is a 3 filament bulb. Or make sure no corrosion is found at the contact poinst for the bulb.

With the lamps switched on, check for power on the Orange wire (comes from the fuse) and on the Brown wire (comes out of the switch) at the Headlamp Switch. If you have power there, verify power at the lamps sockets.
If that tests OK, your next step will be to check the Ground circuit.

Check for a loose wire on the back of the light switch