Hi I was wonder if anyone here could help me clarify something. I have this horn relay on my COE, and there are a bit more wires on it than are shown on the diagram. Can any one recognize it? and know what different wires are. I am not that strong in wiring when it is different from the diagrams.
There's no horn relay in that wiring diagram you posted. The horn is actuated by the switch providing a direct ground to complete the horn circuit. The horn feed is always hot and the horn button provides the ground to complete the circuit.
A horn relay would have a battery feed, a switched hot [wire out to the horn (which is grounded), and a wire to the horn button which grounds the relay coil to pull in the contacts.
Last edited by klhansen; 08/03/20257:52 PM. Reason: fixed fumble fingers
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.
As Kevin says, there was no relay used on that diagram. We do not recognize the part you show. So probably someone has added this part. So now you need to show us good pictures of that part, all it's markings, it's part number and where wires go. Also need to show the horn(s) and how many wires are to them. Then we will tell you the answer to your specific case. Need many good clear, well lighted pictures with explanations of wiring.
Is the wiring diagram COE specific? I don't know about Chevy COEs, but GMC COEs have quite a few differences in wiring from same sized non-COEs. Maybe that is a stock horn relay.
'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.
It looks like a Single Pole Single Throw (SPST) relay. The right side top horn, bottom battery. Left side top horn switch, bottom battery. The horn switch controls the relay coil circuit. Use a test light to see if the bottom two pins are hot. The original relay is a three pin (1116775), one battery feed for the horn and coil.
According to available manuals and diagrams, 1946 "trucks" did not use a horn relay. Some cars with dual horns did. Truck relays came in after 1951. Chevy shows only info for cars and trucks. Truck horns had two wires, one to ammeter and one to horn button to be grounded. The dual horns have one wire to the relay. The horn is grounded at it's mounting. The button is no longer grounding a full voltage/amp load. It is operating a low voltage/amp coil inside the relay. This closes the relay contacts and that is where the full load is switched. I believe Chevy finally realized that switching the full load at the steering wheel was too "sparky" and a stress on the horn contacts at steering wheel. The typical old can relay has three wiring screw terminals. Usually marked B H S. Battery Horn Switch. Then they had a wiring diagram printed on them using 1, 2, 3. Those metal relays need a good ground at their bolted flange to body metal (chassis ground).
That 1116775 relay that JimGMC posted is listed for early GMC COE trucks (300 CF & EF; 350 CC, CF, EF & FF) as well as all later 6v models once they switched to relays like Bartamos said.
Bart: Why would the relay need a chassis ground? Seems to me that the only ground needed is provided by the horn button (Switch) when it is pushed.
Last edited by Bill Hanlon; 08/04/20252:43 AM.
'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.
Here's a wiring diagram for 1954, showing a grounded case horn relay and the notation that it applies to all models except 3742 and 3942 (Forward Control) models. So COE's would have had a horn relay for 1954.
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.
Hello all and thank you for all the replies. This is the wiring diagram I have been able to find. The truck has been restored so there is a potential for things to have been added to the wiring. My truck is running a single horn. I will take some better pictures of the relay and do some measuring next time in the barn.
