Walthers track products are made by Shinohara of Japan. On their older products, the frogs were not insulated and changed polarity according to which way the turnout was thrown, and created a short if your trackwork was not properly insulated from the turnout.
For a fully assembled double crossover, if you mean it has four turnouts and a crossing diamond, it should be fully insulated internally but your adjoining trackwork may need to be isolated from it on one or both ends to prevent shorts.
The only way to know for sure is to trace the wiring using a voltmeter and power pack.
Allegheny2-6-6-6I recently picked up a brand new Walthers code 83 #6Double Crossover. P/N 948-812 at a train show out of state. It's an older version that does not specify "New & Improved for both DC & DCC" My questions are#1 What’s the difference?#2 Can it be used out of the box for DCC?#3 If it does need to be modified is it worth it or should I just get the new generation switch?
I'd start by checking the P/N against the description in the Walthers catalogue or website. Or, you can tell the difference by looking at the frogs. On the DCC friendly version, there will be an insulated gap next to the frog on all rails leading to it. If it is not "friendly," it will take a bit of work. If you want to tackle the job, start here: http://www.wiringfordcc.com/
John Tim