Originally Posted by MercuryZephyrZ7
Its called a Starter Solenoid, if you go to the parts store for a new one. You can bypass this to see if the starter is stuck or not working also. All you do is on top of the solenoid there are two little studs, then on each side there is one big one. You take a screwdriver (WITH and insulated handle...unless you like being zapped) and touch one of the little studs to the large stud that is connected to the wire leading to the starter.
Which little stud will jump it is different on different cars. On my '95 it was the small stud closest to the firewall IIRC. Again, you'll know when you got it right when the truck turns over and scares the crap outta you! If you do this and the starter turns over then your starter is good, solenoid bad. If you do this and the starter just clicks, make sure you have at least 12.5 Volts on the battery and if so your starter is probably stuck.
Make sure it's in neutral if manual and key on. Should turn over if you cross the correct studs. Good luck!
This is why I usually put relay/solenoid, there's always someone who comes on and says its one if you said it was the other. Pretty sure parts stores call it a solenoid but I've seen it labeled as both.
If your going to test it that way and take a chance of melting the metal of your tool or accidentally arc welding it to the posts, feel free. I prefer to use a small section of decent gauge wire to touch the two big terminals whenever I have to test it for someone. That way you ruin some scrap wire instead of one of your tools.
Assuming you have the same one I usually see, the small posts are for engaging the connection between the big posts. If its clicking then its trying to engage but for some reason it isn't working. So if you can jump the big terminals together and get the starter to engage it usually means that part is bad. You can also do some electrical tests, but the quick and easy is to just jump the two big terminals.