Blue permatune

[jimmyjimmy]

I have 2 old blue permatunes,I got with the car I purchased years ago.
One should be good- but still have to try it- but the other one makes a short circuit,the seller told me.
I looked around here but couldn't find a schematic or the components there are in.
What is known to make a failure in those permatunes?
I have also a crane 700 in the car,do they work together well?
Any info is welcome.

Thanks