ULF28 Questions

[Watermelons are cool]

Does anyone know if, when synching 2 Whelen ULF28's, can one be activited and operated normally, then activite a second one and have them both by synched together with the grey wire?

Also, is it just the main 12v input that needs to be fused, or does each lighthead need to be fused off the ULF28?

Thanks!