Have a 1942, bought a steering wheel center horn cap off ebay but it is too large. I have read the wiki on horn button, I have the parts that go on before the wheel, but the cap is too large to recess in the wheel and does not seem like the center part where the clip goes will hook in because the cap is too big.

I dont think I need the COE horn button, but how would one know? I have the features of a deluxe style cab, such as center windshield crank, throttle button, choke, ignition etc in the center but this is throwing me for a curve. Thoughts? This is a fire engine

Am I just doing something wrong?