Battery Ground Cable Switch

They commonly give problems with age. You can replace it with an aftermarket battery cut-off switch, may require some creativity to install one nicely. Most just get rid of the switch and bypass it.

 

on my 89 't' my just melted down the other day. Everything seems to work a little better now. I suspected that it was providing a voltage drop and do not plan on replacing it.

 

Eliminate the switch from the circuit!! I had the same problem with an '84 Mondial QV that I owned, had lots of electrical gremlins. I bought new positive and negative cables, and routed the negative side directly to the chassis, bypassing the switch completely. Make sure you clean the metal surface on the chassis really well with emory paper, so that the cable makes as good a connection as possible. I then sprayed the battery terminal and the cable connection at the chassis with a battery corrosion protectant.

The switch, even when it is "working" puts so much resistance in the line that you are losing power. As soon as I made that one change, a lot of my problems cleared up, especially the starting problems I was having. Also, be sure to check the fuse panel -- the old Mondial fuse block is notorious for connection problems, delamination of the circuit boards, and burned out wires. You might want to re-route some of the high drain items, like the fuel pump, away from the fuse block all together.

Hope that helps.

BTW, old car rule of thumb -- 95% of all electrical problems can be traced to a bad ground.