1988 420sel Ignition
 

1986 420sel Ignition problem
I have a 1988 420sel, I am getting frustrated when I turn the key to start the car the radio comes on and lights come on as it should but it will not engage the started. I ran a wire to the starter and when I hit the rigged starter button I installed it starts with no problem. When I go to turn off the engine I turn the key and it shuts down as it should, So far I have replaced the starter, installed a new neutral switch changed the ignition module and still having this problem. Could it be the ignition switch itself ?? not sure any help would be appreciated it before I just junk this car, Thanks!!!!!!!!!!!!!!!!!:silly:

Go and buy a cheap voltmeter (or borrow a friend's) and trace the circuit to see where you are loosing the starter signal.
Battery power is fed to the ignition switch pins 3 and 5 (sounds like you have power here). Power comes out of the switch on pin 2 (violet wire) in the start position and goes to pin 8 of the park neutral switch and out at pin 6 (violet/white). From there it goes to the starter solenoid. This is a simple series circuit, so a break anywhere in this string will cause your problem.
Some cars have a relay in the circuit as well, but the manual does not show one for your year and model.