How long should the flex tube be from the horn to the bulb? Any pix of the proper way to route it ? How about the size of the rubber bulb ? Thanks for your help !

I mounted mine a bit forward of where it should be. See here:

http://www.mtfca.com/discus/messages/411944/496499.html

According to Ford, the tubing exclusive of the mounting bracket but inclusive of the two ends on the tubing was 20" long.

The two horn mounting brackets in Royce's first two photos are reproductions. They look similar to the originals, but are not correct.

As far as the bulb goes, the correct size is a #11. That is 7-3/4" long, including the 2" sleeve, and 3-5/8" at the largest diameter. The thread in the sleeve is 41/64" x 27 tpi, which is what Ford specified. They changed to a more standard 5/8" x 28 late in 1915, right at the end of the bulb horn's appearance on Fords.

(This is why correct, original Ford horn parts don't always thread together nicely. You probably have a mix of early and late parts. The late threaded parts were specified "For Repairs" but the records are silent about how to make the different threads harmonize. Probably you were expected to buy everything new. Kinda like today.)

Here is a photo of the correct bulb, made from the Ford print:



I make these. PM me if you're interested.