Sounds like a battery cable issue to me too. The trip odo and clock should be on constant +, not switched by anything, so I doubt the relay had much to do with it. Could be the shock of the hood closing shook the cable back into place. If the battery terminal clamp is loose or corroded, it can work well enough to light up the dash until you turn the key, at which point the additional load burns out the spot that was making a connection and everything goes dark. If the terminals are tight, pull them off and make sure they're clean inside, they can corrode in between and cause the same issue (happened on one of my dad's trucks once). If the terminals are clean and tight, and the cables feel alright, check any big fuses in line with the + cable for any obvious looseness or corrosion.