This topic has probably been covered a hundred times but using search didn’t help. My maintenance manual discusses a single wire horn and relay but mine has 2 wire terminals and no relay. Neither terminal is connected to the horn case and ohmmeter confirms that. Pushing horn button applies 6v across the 2 wires. Nothing happens at the horn, no mechanical action or sound. I don’t know how the horn should normally operate so I don’t know what to look for. Here’s a couple pics, please help me out.
Any resistance across the two terminals? If not, the vibrating contacts need to be cleaned up or the coil may be burnt out. (also check continuity across the contacts)
When voltage is applied, the coil pulls on the sounding plate on the horn and at the same time opens the vibrating contacts, shutting off the current flow to the coil, which lets the contacts close again, starting the cycle all over till you let off the button.
Kevin 1951 Chevy 3100 work truck Follow this saga in Project Journal Photos 1929 Ford pickup restored from the ground up. | 1929 Ford Special Coupe (First car) Busting rust since the mid-60's If you're smart enough to take it apart, you darn well better be smart enough to put it back together.
Pushing horn button applies 6v across the 2 wires.
Stock horn wiring would have -6v going to one terminal on the horn at all times. The other terminal would also measure -6v until the horn button was pushed which would ground this terminal letting current flow through the horn and causing noise.
'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.
Get someone to hold the horn button down and measure both terminals on the horn to ground. One SHOULD show battery voltage and the other SHOULD show zero volts when the horn button is pressed. This is not how I understand your statement above "Pushing horn button applies 6v across the 2 wires".
'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.
Get someone to hold the horn button down and measure both terminals on the horn to ground. One SHOULD show battery voltage and the other SHOULD show zero volts when the horn button is pressed. This is not how I understand your statement above "Pushing horn button applies 6v across the 2 wires".
An easier way to do that is to just short the terminal that's not hot to ground (bypassing the horn button and the need for a second person.) If the horn works then, the problem is likely at the horn button.
Kevin 1951 Chevy 3100 work truck Follow this saga in Project Journal Photos 1929 Ford pickup restored from the ground up. | 1929 Ford Special Coupe (First car) Busting rust since the mid-60's If you're smart enough to take it apart, you darn well better be smart enough to put it back together.
An easier way to do that is to just short the terminal that's not hot to ground (bypassing the horn button and the need for a second person.) If the horn works then, the problem is likely at the horn button.
Problem with doing it that way is "which terminal is not hot". Both should be hot until the horn button is pushed.
'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.
Problem with doing it that way is "which terminal is not hot". Both should be hot until the horn button is pushed.
Agreed, you just have to either disconnect the wire to find the "input" hot one or trace them. You can still be working alone to do that.
Kevin 1951 Chevy 3100 work truck Follow this saga in Project Journal Photos 1929 Ford pickup restored from the ground up. | 1929 Ford Special Coupe (First car) Busting rust since the mid-60's If you're smart enough to take it apart, you darn well better be smart enough to put it back together.
Agreed, you just have to either disconnect the wire to find the "input" hot one or trace them. You can still be working alone to do that.
Agreed and a good idea.
By the way, I have a '51 (not '50, but I'd bet they would be the same) GMC Maintenance manual that has about a page of how to adjust and troubleshoot the horn. If you are interested Mike, I'll post it or send it to your e-mail. Current draw at 6 volts is spec'd at 9 amps and horn frequency is 302 cycles per second.
'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.
Thanks guys, I got the horn working on the bench but found my horn button has way too much resistance to give a good ground. I’ll need to get it cleaned up. The diaphragm vibrator contacts sure do spark a lot.
Bill, if your manual is specifically for a 1951 I would like to accept your offer. My manual covers several years and the adjustment procedure doesn’t seem to apply to my horn.
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.
Last edited by Bill Hanlon; 01/19/202310:17 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.
About 10 years ago (right after I bought my '52 GMC) I replaced the defective horn switch (it was shorted) with a new (probably Chinese) switch from one of the OldTruckParts companies. Put the new switch in and instead of honking all the time it never honked. Further inspection showed that someone had decided to paint the upper contact piece. Some 240 grit Emory cloth knocked the paint off of the contact surface and it has been working well since.
'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.
eBuy a few years ago if I remember right. There is one there now for $40. Use "51 GMC Maintenance Manual" for a search term on eBuy and it will be the first thing that pops up.
'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.
