Anybody ever seen something like this?

[jholl24]

I cleaned my battery terminals today, and while taking the nut and bolt off the "hot" post I noticed a spark.
After I was finished, I tried to start my pickup, but it wouldn't hit a lick. So I assumed I had blown a fuse. They all checked out.
I looked under the hood and noticed this plug next to the "hot" terminal. I touched it to the post and the truck fired right up.
Anybody know why this is rigged up like this? I bought this 95 pickup about two months ago and never thought anything about it. Its a great running truck, but this setup is bugging me a bit.


[img=http://s16.postimg.org/5faj0w5z5/0526141909.jpg]