You most likely have a switch on the Playfield that is closed that should be (NO) Normally Open. Look on your Playfield for what scores a 1000 points and that will lead you to the problem.

Ken

Read this: http://www.pinrepair.com/em/index3.htm#motor especially 3F + 3G

Williams Start-Up Sequence.

When the start button is pressed, the credit unit is decremented. This is done through the credit unit zero position switch and the 2nd coin relay (and the ball count zero position switch).
The end of stroke (EOS) switch on the credit unit decrement coil will energize the coin relay.
The coin relay will trip the game over relay.
The coin relay will energize the reset relay. The score motor will run.
The reset relay will energize the ball count unit reset, through the score motor.
The reset relay energizes the 2nd coin relay latch and game over relay latch coils.
The reset relay will energize the score reset relays, through the score motor.
The score reel reset relays will zero the score reels, through the score motor. The score motor will continue to activate the score reset relays until all the score reels reach the zero position.
The reset relay activates the bonus unit coil until the bonus unit zero position switch is activated.
When the bonus relay drops out, the outhole relay is energized through a different bonus unit zero switch and score motor switch.
The outhole relay will run the score motor. The bonus unit will step up once. The ball will be kicked to the shooter lane.
To me it looks like a stuck reset relay? Pin-it

I would look closer at the 0 position switch on the 1000s unit

--Jeff

Agreed..this is the most likely issue.

The bo

(#1)I believe the location of what your looking for is at the rear of the playfield (underneath)there are six coil/relays (closest to the backbox) and look for the bonus contact that is either not separating or the armature plate is catawumbus (not allowing proper function

Not really we all learn from just working on these em s its
just that they put the circuits in a little bit different location & function between models but you will figure it out . We all do. If that did not work (#1)Something i would try too is to disconnect the jones plug that operates the playfield circuitry thus separating that part of the equation as to narrow down your troubleshooting dilemma.

That has me a bit puzzled i will try to replicate on mine.

On that jones plug disconnect procedure:

The one way to make sure that it is within the playfield circuit but i am sure that bonus relay is likely the problem. The OEM usually puts paper labels of the actual function of the coil/relay as long as the glue did not let go or someone removed them, you should have no problem. I just replicated the same thing & got your symptom also. Look REAL CLOSE at all contacts . If you can send photos it may help us a little bit better.

You can download the manual and the Schematic here for free.

http://www.ipdb.org/search.pl?any=grand+prix&search=Search+Database&searchtype=quick#1072