Fixing a Failed Lamp Fuse.
If the game is blowing a 6 volt lighting fuse, that is often caused by a shorted light bulb or light bulb socket. Or a wire for the GI (general illumination) is touching the metal frame of the game. This will of course blow a fuse, and these problems can often be hard to find.
Look under the playfield for a lamp socket that has the "tit" bent over accidentally and is touching the "base" of a lamp socket. This is common on lamp sockets on the edge of the playfield, because the playfield can be accidentally lower at a slight angle bending a lamp socket. Also if you took all the parts off the top of the playfield to clean it, check all the lamp sockets incase something metal fell inside a socket.
The easiest way to find a light short is to make a small "cheater" out of a small circuit breaker. Take a blown glass fuse, and solder the small circuit breaker to the ends of the fuse. Now insert the fuse into the game and turn it on. If there is a short, the breaker will 'blow' and can be reset. This makes finding the short in the GI circuit A LOT easier (and cheaper since you're not replacing the fuse a million times.
Now to find the short. I break the circuit down into "half". That is I cut the GI wires as they enter the playfield (in the case of a playfield short), and power on. If the fuse does not blow, I add 10% to the string and re-cut. Keep doing this until the short if found.
Also it's a good idea to do a visual inspection of each lamp socket. Remove all the light bulbs too (you were going to replace them all with new #47 bulbs anyway, right?) If the fuse stops blowing with all the bulbs removed, then there was a shorted bulb. Replace the bulbs one at a time with the game turned on to find the culprit (or just install new bulbs). Sometimes flashing #455 bulbs can short too. If the light fuse still blows with all the bulbs removed, there is either a shorted socket, or maybe a short at a connector (see the section below on connectors).
****this was copied word for word from
http://marvin3m.com/em/index2.htm#low ****