Click,Click,Click!

Just an example of a simple problem threw me for a loop for a few minutes. 86 Ranger, one day won't start. Acts like dead battery/ bad connection, BUT THE HEADLIGHTS stay on nice and bright.

Problem? The NEG battery cable, came off the battery, went down and a factor "T tap" bolted to the frame, and then same cable ran over and bolted to the engine. The cable was all corroded inside near that "T tap." It carried enough to ground the headlights to the frame, but the section going over to the block was "done."