I saw the Moe's Taver mod and wanted one. Looked like they were hard to come by so I did my own with the parts I had on hand. Came out nice enough, and it is easy to do.

Stuff needed:
-LED that can be separate from housing. I used a flex from Nifty: http://www.niftyled.com/Flex/555-Super-Bright-Flex-Blue-p137.html
-Wire. I used 22 gauge, about 2' length (times 2).
-Heat shrink tubing and heat gun
-Solder and soldering iron
-zip-tie

Directions:
1. Get a flat/flex LED separated from a 555 housing (your color choice).
2. Solder wires to the connections , cover solder join with shrink wrap tubing, cover two wires with shrink wrap tubing (makes it look neater)
3. String through the playfield hole where Moe's Tavern switch wires run
4. Position and zip-tie to Moe's Tavern gate
5. Connect wires to playfield lamp of choice. I went with "Moe's 2x Scoring" playfield lamp so the sign flashed when that was flashing.

Total time 30min.

Total cost: $1.10 for LED. Shrink wrap tubing, solder, wire I had around, but can run you a couple of bucks.

Flex LED removed from housing. Attached leads with alligator clips for testing.
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Mounted behind Moe's sign. View from top.
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Mounted behind Moe's sign. View from side. Can see where the zip-tie is holding the wire in place and how the wire runs down to playfield with ramp's gate switch wires.
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More picts

Under playfield wiring. Black shrink wrapped wires run from playfield hole to "Moe's 2x Scoring" light. You can zip-tie to existing wire bundle.
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Wires attached to "Moe's 2x Scoring" light socket.
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Completed front view of Moe's Tavern sign. Blue LED may not be what everyone wants, but I like it.
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Another shot of the completed sign.

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Wow -- this was the first DIY mod that I wrote up for pinside. Glad people find it useful.