Quoted from KingPinGames:
you need either a 2400 or 2600 series bill acceptor. the 2500 series (which is what you have) is for vending machines.
Here's a summary of hte model number-
It is broken down into:
The first two are the usage. 'VN' is 'Vending'. 'AE' is Amusement. Vending models offer coupon coding, and come in 24v MDB models. Amusement models don't.
The third digit is the 2xxx model range. Only 2xxx models will fit pin doors.
The 4th position can be a 3 through 8, and are called (and accept [$ bills / directions]):
3: Economy [1, 2 / 2]
4: Reference [1, 2, 5 / 4]
5: Economy Reference [1, 2, 5 / 4]
6: Premium [1, 2, 5, 10, 20 / 4]
7: Recycler Ready [1, 2, 5, 10, 20 / 4]
8: Reference Expanded [1, 2, 5, 10, 20, 50, 100 / 4]
The 5th position is the bezel. Only numbers 1 or 4 will fit in pin doors. Faceplates are, for the most part, interchangeable.
The 6th position is the voltage. WPC Machines (and maybe 2000-2010's Sterns?) only accept 110v, so this digit must be a '1'.
The 7th position, if present, is an 'R', and means it came with a Recycler unit. Pin games, and AE models do not support Recycler units.
The first item after the dash is either 'U' or 'D', indicating Upstacker or Downstacker.
The second position after the dash is the size of magazine that the unit was shipped with. Interchangeable, and various sizes can fit depending on game maker.
The third is the harness shipped with. Usually, an 'E' is required, the "9-pin VFM Style / Single Price" harness.
The final 'XX" is the country code. Usually, 'US'.
Now, as you can see on the label - and remember, pin games can only accept pulse interface - dip switches #7 and #8 both need to be OFF. You also will need to check your harness - make sure the proper pins are connected up. It's recommended to have it 1 pulse per dollar, as well, but will require the correct coin input to be wired to, and the game knows the value of said coin input.
If it's accepting bills, but not registering credits (again, need more than "they don't work"..), then it's possible that the serial line is being output and not the pulse wires. (In other words, wrong harness!)
If anyone is interested, I have a full document spelling out the model numbers available, and I'd be happy to forward it to anyone interested.