Remove the relay. Check the voltage on the female terminals in the relay plug. The should be 12 volts on one small and one big terminal. Use a jumper wire between the two big female terminals, it should be a fair sized wire because it will carry the headlight current. Do the lights now work? If they do check the relay as follows. The Toyota relay should have two big and two small terminals. The small terminals are the switching terminals for the relay coil. If you have a battery charger or any 12 volt supply you can check relay coil operation. Hook the red battery charger clip to one small terminal and the black clip to the other small terminal, polarity doesn't matter on a relay. You should hear or feel the relay coil energize. If you have an ohmmeter check that there is 0 ohms resistance accross the two big terminals. You could also run a jumper from the small terminal with the red battery charger clip to one of the big terminals and measure the voltage on the opposite big terminal, it should have the same voltage on both sides. You really need wiring diagrams for your truck top locate the problem. I'm linking you to a 2003 shop manual, it should be close enough to your lighting circuits to help.
http://fsm.afraid.org/
Look for headlamp circuits in the wiring diagram to get an idea of the wiring layout. The tail lights are on another diagram. You should have another relay in the tail lights. You can look at the lighting circuits in volume II to get some ideas on testing each component.
Note there are separate relays, fuses and bulbs in the two lighting systems. The common components are the ECU, (2003, I assume 96 is similar), light switch and ground circuits into the switch.
Hope this provides enough information to get you started.
Clifton