This skull was part of of $35 skull and bones pack from an eBay seller.
You can put the resistor in series with either speaker wire.
This reduced the volume to a more reasonable level.
I want each prop to be somewhat localised and not hear them all over the yard.
The input voltage can now be anywhere from 9V to 30V DC.
It also interfaces to the “try me” button wiring and provides a standard trigger method.
An opto-coupler is employed to convert the new voltage trigger to a contact closure.
In other props I’ve used a section of large heatshrink instead of tape.
I simply forgot to put it over the wiring before soldering the tail on!
This will connect to a remote power supply and trigger circuit.
Zip ties on the inside and outside provide some strain relief.
Here it is being power from 12V. The trigger voltage was also 12V.