I have a 72 Cutlass S and the turn signal/back up/seatbelt fuse is out. Trying to see if anyone has had the same short problem. I've unhooked the wiring to the back under the steering column, so I know that is not it. Since the seatbelt warning is hooked up to it, I get to hear the great buzzing sound also. What a treat. Just hoping someone might have a suggestion to this nightmare.
The fuze busts as soon as i turn the key on.

 

Check the bulbs from the sockets for the turn indicators and back up lamps. One of those sockets could have corrosion in them and with the bulb installed they may be the short. Or it could be the brake light switch, usually down low on the steering column someplace.

 

I unhooked the entire wiring harness from the back under the steering wheel, because initially I thought it was the intermediate harness being chaffed. But I unhooked the whole harness that leads to the back under the steering wheel and the fuse still blows. I'm thinking it might be the turn portion in the steering column.