playfield wiring schematics say "coil diodes are 1n4004 switch diodes are 1n4148"

http://www.ipdb.org/files/853/Bally_1985_Fireball_Classic_Schematics.pdf

Either will work fine. We switched to 1N4148 diodes for the switches to save a penny each.

You can use the 1n4004 for both coils and switches, per this post: https://pinside.com/pinball/forum/topic/tilt-not-registering#post-4317733

The 1n4148 were likely used for cost. $1 at Great Plains Electronics gets you 50 of the 4148 (2 cents each), 20 of the 4004 (5 cents each). An insignificant difference when you're using 20 a year but if you're a factory using tens of thousands it's worth using the cheaper diode.