W250 auto
Wouldn't start, no power at coil.
Checked fuses, had a blown 25 amp (stop/signal)
Replaced it and had voltage at coil.
Next day same thing, no start, no voltage at coil
but fuse is fine. (coincidence)
What is causing the intermitent power to coil?
Can I hot wire it with key on voltage?

Thanks !

Check the ECU. With colder weather, a weak capacitor can do this.
If your check engine light does not come on during the no-start, that may be your problem.
http://www.jeepforum.com/forum/f12/crash-course-brain-surgery-replacing-capacitors-ecu-492597/
AS said, a bad ASD relay is a possibility

http://www.allpar.com/fix/codes/sensors/auto-shutdown.html

Is this the relay next to the Fuel pump relay attached to the inside fender in the drivers side? I had an issue with the fuel pump
getting low amps and "solved" it by splicing in a new ground at the pump to the frame.
During the trouble shoot, I unplugged both of these relays looking for corrosion, cleaned the terminals, cleaned the body grounds.

I'll replace it and go from there.
IF that doesn't solve it, can I run a seperate 12v source to the coil?
(12v with key on)

Thanks !

IF there is a problem somewhere in the wiring the computer may shut down that part

I found out the hard way( as usual) when I wired the VSS on my Dodge -55 that use a Jeep/ Van/ Dakota combo of parts, I lost power to the coil and distributor , when I got the VSS wired the right way the other problems magically disappeared

Just so happens that when I was dealing with the fuel pump issue
I picked up a fuel pump relay from Napa. Wouldn't plug in, the indexs
weren't right, but it did plug into the ASD. Pulled it out of the box and swapped out, problem solved for now.
I found the wire (grey/orange trace) that goes from the
relay to the coil, so if it happens again, I can run a jumper
to ge me back home.

Appreciate the responses !