Manual is GMC X-5111, 1951 specific. If I had to bet it is probably 95+% same as 49-53. I have attached scan of 4 pages that have to do with the horn. Downloading the file will result in easier to read (larger) pages than just looking at them here in StoveBolt's PDF reader.
Attachments
IMG_20230119_0001.pdf (4.59 MB, 11 downloads)

Last edited by Bill Hanlon; 01/19/2023 10:17 PM.
'57 GMC 102, Original 347 V8, HydraMatic, 3.08 rear gear, added A/C, disk front brakes, HEI, AFB carb, '98 Honda Black Currant paint. T-boned and totaled 10/12
'52 GMC 152 Stake Bed, Original 228, SM420, added A/C, HEI, disk front brakes, '67 Chev 3.55 rear gear. Gets used as a real truck.