Anyone know about the electrical wires on a 1981 Ford F-100?
if its a 3 wire solenoid then the two big wires go to the starter and the battery positive post,the small wire comes from your ignition switch,if its automatic it goes thru the neutral start switch as well if its a four wire the nthe extra small wire goes to the alternator field terminal to supply power to energise the alternator for charging
For your question, I'm going to assume that you are installing an aftermarket stereo. This being said, you will have to break out the ole' test light. You are going to want one wire that has constant voltage, even with they key off. You are going to want another wire that only has voltage with the key either in the on position or accessory position, but not while the key is off. The third wire you want to have is a ground. 1. For the constant voltage wire (voltage all the time even with the key off), take your test light and hook the clip part to a known good ground (Metal part of the dash, make sure it's getting a good ground or else you will get irritated when the light doesn't light up.) With the key off and removed, touch the light to all of the wires. You should only have one of the wires that are hot. Remember which wire this is because it is going to go to the yellow wire on the aftermarket radio harness. 2. For the ignition hot wire (voltage only when the key is in the on or accessory position) You want to turn the key on and touch the other wires. Find one that lights up, then turn the key off and the light should go off on the test light. Remember this one because you will be hooking this one up to the red wire on the aftermarket stereo harness. 3. For the ground wire, hook your clip end of the test light on the constant voltage (voltage all the time) wire. Touch the pencil tip end to the ground wire. If it lights up, it is a good ground. Hope I helped! Happy installling! )
The two large cables, one goes to the battery, the other goes to the starterThe two small wires, one goes to the start connector at the IGN switch, The other goes to the coil as a direct 12v for better spark for starting. ( when you release the key from start to run the 12v supply goes to the coil via a resistor wire) This set up assures better spark for starting.
go to auto zone web site they have a lot of self help manuals for free.