From the pinwiki link listed above. Start here:
http://www.pinwiki.com/wiki/index.php?title=Bally/Stern#Bally_.2F_Stern_MPU_Board_LED_Flash_Sequence
5.5.4 Bally / Stern MPU Board LED Flash Sequence
Upon start up, Bally and Stern boards have an LED that flashes. The LED is used to convey the results of specific tests conducted on various parts of the system. This section explains what is being tested and how, according to information from the Bally "FO-561-2 Theory of Operation rev. 5-1982" manual, and the Stern manual "Theory of Operation, Stern's Microprocessor Controlled Solid-State Games".
When power is first applied to the MPU board, the LED by default is ON. The very first set of valid instructions in every Bally / Stern game is to turn the LED off. This is more of a flicker than a flash, so is not counted as a flash in the 7 flash sequence.
5.5.4.1 Quick summary
Flicker: MPU reset good, program booted.
1st Flash: ROM Checksums OK
2nd Flash: U7 6810 ram OK
3rd Flash: U8 5101 ram OK (U8 & U13 on mpu-200)
4th Flash: U10 PIA OK (see details for caveats)
5th Flash: U11 PIA OK (see details for caveats)
6th Flash: U12 555 Display interrupt timer OK
7th Flash: Zero crossing interrupt detector OK (solenoid voltage present)
The LED isn't flashing based on what you're telling us. It just stays lit when you turn the game on correct?