L/F Big Boy Part

[Jim B]

I am looking for Part #4 for the Revell Big Boy locomotive. I think it’s the whistle, but I’m not exactly sure. I contacted Revell, but they don’t have the kit or the spare parts anymore.  ☹️ Any help will be greatly appreciated

[Little Timmy]

Can you post a picture of the part on the instruction  sheet ? 

Also, what scale ?

 

[Jim B]

It's the Revell HO scale kit:

And it's P/N 4:

It might be some sort of generator for the headlight?  Not totally sure.