My P 30 van's flashers, dash panel, tail and brake lights do not work.

Check the ground connection, if worst come to worst, get some wire and jump the ground all the way back to the battery. Older vehicles often have tenuous ground connections if things have rusted or been in an accident. once you know its not the ground for a section of devices, start continuity testing all the way out to the component not working. But it’s likely the ground. Or actually check the hot wire first: is it hot? if not, hook it back up.