Electricity is pretty simple stuff, at the basic level. It's like a bottle of electrons ready for a "hole" to flow through. The pressure, flow and potential really don't matter at the basic level; it's just theoretical stuff and not really important for what I'm trying to describe.
When the "hole" is planned, and the outlet is a certain size, the work for the electricity to accomplish is under control. If it's a light bulb, the electricity flows through the bulb, the electrons either heat a filament, or excite a field, and any extra flows to the ground. The same holds true for automobiles; any work to be performed is under control, but there is one stipulation that can lead to all types of strange things: the ground.
When the ground isn't good, or none exists, things stop working, or worse: things do things unintended. The electricity doesn't travel the intended path; it can even travel "backwards"; finding a path that may make a left turn signal flash dimly on the right. If it's the electricity to run the starter motor, it may be enough to make relays work, but not enough current is allowed to turn the motor, or just enough to make the bendix chatter. I think a ground problem may have materialized on a truck at work.
Everything was fine, but the fuel filter started leaking onto the manifold. We stopped the truck, made the repair, and that's when things became strange. The ignition would work; then not. The voltage was correct; then not. lights acted strangely, or shut off. The batteries are new and at 13 volts, so I don't think that's the problem
I scratched my head, until I had enough, dragged the truck off the road with a backhoe, and started thinking about the problem. Past experience slapped me around for a few minutes, and I had a eureka moment: "It must be a ground problem." So, I had every intention of starting with the main ground from the battery to the chassis. It's an old truck; and it wouldn't hurt to remove the ground strap, check the connection and reattach it to the frame....but it started raining.
So, tomorrow I'll find the time to see if I'm correct. If not, I'll either look for other problems, or burn it on the side of the road.....not really....although it crossed my mind as a solution that would make me feel better.
In Case You've Wondered
My blog is where my wandering thoughts are interspersed with stuff I made up. So, if while reading you find yourself confused about the context, don't feel alone. I get confused, too.
If you're here for the stories, I started another blog: scratchingforchange.blogspot.com
One other thing: sometimes I write words you refuse to use in front of children, or polite company, unless you have a flat tire, or hit your thumb with a hammer.
I don't use them to offend; I use them to embellish.