how do I troubleshoot my1994 3/4 ton vandura conversion van's brake light proble

First check your brake fuse for open. If o.k. then check your brake switch's power and ground circuits. If they are o.k. make sure the brake switch is adjusted properly. If no power out of brake switch it is probably a bad brake switch. If you have power out of the brake switch, make sure the bulbs and sockets are good and check the circuit from the brake switch to the brake lights.