I've got a '99 4Runner, about 95k miles. It just started (in August!) having trouble cranking. First suspicion - battery. Then I thought about it - why would a battery drain in the summer. So when I popped the hood, I could hear something like 'sparking' or arcing coming from the module right behind (towards rear) of the fusebox (battery=> fusebox=> this module). First, what is that module, and secondly, anyone know why I have an arcing sound coming from it? I disconnected the battery, and of course the arcing stopped. Being an electrical engineer, I thought I could diagnose the problem. Even with the battery disconnected, there is still intermittent continuity between the two battery terminals. I assume that's not right.
Thoughts anyone?

 

When does this arcing happen? Driving? Random?
Have you hooked up a multimeter to try to track down how much current draw?

 

Thanks for the reply. I haven't done that yet. I am going to try a new battery and see what happens. I wonder if some of those active circuits in there act funny when there is a low current through them.
Ben

 

So....If anyone's interested, I contacted a family friend who is a mechanic. He said that it was the solenoid inside the vacuum module for the 4WD enganement system. They do weird things when the battery dies. Guess it was a dead battery after all!
He also said that he replaces more batts in the summer than winter, contrary to what I thought.