Ok, it's a Ford Aerostar XLT. 1996
Fuse location 8
It doesn't say this controls the shifting from first gear in my book, but when the car won't shift to second gear, the fuse blows...don't know if it's the cause or effect.
We're using a blue 15amp fuse.
That's the cause. This fuse (which is hot at all times) supplies power to the instrument cluster which in turn sends a vehicle speed signal to the powertrain control module (the computer) which controls the transmission.
In other words, when this fuse blows, it doesn't know how fast the vehicle is going, so it can't shift the transmission.
Let me continue to study this wiring diagram and I will get back to you with my ideas as to where the problem lies in just a little while.
Fuse 8 is a 15 amp fuse which supplies power to the following circuits:
Left/Right Vanity Mirror Lamp and Switch (I think these are the mirrors on the sunvisors)
Sliding Door Dome/Courtesy Lamp Switch (does this fuse blow when the door is opened?)
Right Dome/Courtesy Lamp Switch (same question as above)
Glove Box Lamp and Switch
Radio (!!!) do you have an aftermarket radio installed???
Main headLight Switch (feeds the dome/courtesy lamps through the mail light switch when it's in the dome light position)
Instrument Cluster
Based on this, I would verify that the dome lights are not causing the problem by replacing the fuse without opening the doors and then turning the headlight switch to the dome position to turn on the dome/courtesy lights. If the fuse then blows, the problem is in the dome/courtesy light wiring.
If you have an aftermarket radio installed, whomever installed it may not have properly taped/insulated the connections and the short may be due to that.