Ford Repair: 1986 Ford F150 4x4 Starting Problems, core plugs, poor connections

Question
hi my name is jon and i live in hawaii where i purchased this 1986 Ford F150 4x4 inline six 300cc motor.. Everything was good until now!!! Its got about 145,000 miles on it before the oil pan started leaking and core plugs rotted out, so i pulled the motor got everything repaired and put it back in...  now im ready to start my engine turned the key and its turns over no problem then i go to turn off the key then disaster happens, the engine is still turning over!!!! My ground wire melts.. the small 10 guage wire from the body to the block.. so i figure my starter is shot, might as well change the solenoid too.. so i did!!  checked all my ground wires made sure the positive wire is properly mounted, checked the switch on the steering coloum made sure the spring was engauging and went thru every wire in my wire loom to make sure it all ok and not melted together causing a short.. checked all connections checked for 12 volts and for proper ground where needed.. made sure my alternator was hooked up, also replaced the coil... hope that is enough info for my question.


Why is the motor turning over when the key is not even in the ignition?

Answer
first the motor turning over with no key-you probably had a weak battery or poor ground-did you paint the block? if so paint where the ground cable mounts can cause a poor ground-bad cables,cheap cables,cable ends rusted,corroded cables can all cause poor connections or current draw problems-basically most of the time poor ground or weak power supply to starter caused the points in the solenoid to get hot and stick so when you turn off switch the points are still stuck therefore supplying power to the starter-being as is your ground is what melted you had a poor ground.

after rectifying that problem check-for blown fusible link wire at solenoid you can do this by gently pulling on small wires mounted on hot side of solenoid to see if they stretch if so the fusible  wire is blown-check with test light to make sure you have power from battery to solenoid-then when key is turn to start position you should have power on the small wire with elbow connector on solenoid if you do then you should have power coming out of solenoid to starter also when in start position. good luck.