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Posted By Discussion Topic: burning horn wire-1937 model 78-750     BRL 05-31-2023 @ 9:01 AM reply profile send p.m. New Member Posts: 102 Joined: Oct 2021 Hi Guys: My 1937 Phaeton (model 78-750), original design 6V system-positive ground, has started to burn the passenger side horn wire. As a newby to this car, I dont have a complete understanding of all the components to the circuits involved. First off, let me describe a series of events that has made this problem come to light: So I bought this car from a guy and it ran fine except he told me the high beams did not work when the light control at the horn button was set to high beams...OK, no problem I figured I would fix it later. I started to look at the headlight wiring harness and I noticed that the harness and the headlight pigtails were all getting very old (wire jacket faded and falling off and wire colors very faded, bullet connectors replaced and connections feeling loose and looking corroded). I also noticed that there was only one horn installed, drivers side, (this car is supposed to have 2 horns) and the two wires connecting to the passenger side horn were just hanging down loose. The drivers side horn did work though. So I thought that what was needed here was simply a replacement of the headlight wiring harness and a replacement of headlight pigtails and correct bulbs. I also decided to get another horn for the passenger side. I found one on Ebay and it looks just like my drivers side horn which appears to be original (the horn internals look just like the exploded horn picture in my "The 1937 Ford Book". So I took the back cover off both horns and cleaned everything and soldered on new horn pigtails. I tested both horns on the bench and one has a higher pitch than the other and so I thought to myself this was a lucky find and was ready to reassemble everything. So I install the new headlight harness, horns, and headlights. I connect the battery and within 10 seconds I see smoke coming from the bottom of the radiator. I immediately disconnect the battery. While disconnecting the battery, I start to hear a groaning noise that sounds like a horn trying to work. I take everything back apart and what I see is that the yellow wire for the pass side horn has burned away its insulation in the headlight harness. The blue wire for this horn in the headlight harness is OK. All other wires in the headlight harness are OK, including the wires for the drivers side horn. All this has happened by simply connecting the battery and not touching anything else. I take the horns apart and they look and test OK again. I take the headlight switch off the bottom of the steering column and after inspecting the internals of the switch and the bottom center contact for the horn (where the blue wire connects) it all visually appears OK and the internal springs all seem to be OK. The only obvious thing I see is that the yellow horn wires in the new headlight harness are smaller gauge than the wires in the old headlight harness. So as a troubleshooting test I install the new headlight harness back in the car with the old heavier gauge yellow horn wires, and the horns as well. I hook up the battery and observe and touch the wiring...all is quiet and there does not appear to be any burning or heating up of the wires...I continue observing for a few minutes and nothing happens. So I start to think that maybe the gauge of wire was wrong in the new harness or I did not assemble the headlight switch correctly on the steering column the first time. I press the horn button and I hear a low sounding honk...it sounds as if only one horn is working. I start to play with the light control at the horn button and notice that the parking lights work and the low beams work but still not the high beams. After a few minutes more I get out of the car and ponder what the next step is...just then I start to see smoke coming from the bottom of the radiator again and start to hear a low horn groaning sound and I immediately disconnect the battery. An inspection shows that the yellow wire to the passenger side horn is burning up again. The burning seems to be mostly at the connector where this wire connects to the engine/dash harness where this wire ultimately goes to the starter switch. All other wires still look OK. So I am not sure what the problem really is and what troubleshooting I should do next. Please advise. TomO 05-31-2023 @ 10:59 AM reply profile send p.m. Senior Posts: 7250 Joined: Oct 2009 Burning of the wire is caused by excessive current flow. I would start by using an Ohm Meter to try to find the short. With the battery yellow wire to the PS horn disconnected, connect your ohm meter between the PS yellow wire and ground. Rotate the ohm settings to see if you can get a reading on the meter other than open. If you cannot get a reading, set the meter on the highest scale and try flexing the harness to see if you can get a reading. If you cannot get a reading on the ohm meter, disconnect the blue wire from the horn and connect the yellow wire to the horn. Connect the ohm meter between the blue wire and ground. Look for a reading. If you do not get a reading, flex the harness to see if you can get a reading. If you get a reading on either wire, check the harness for signs that it has been penetrated by some metal causing the short. If you do not get a reading from either wire, try using a jumper wire from the NEG side of the battery to the terminal on the PS horn where the yellow wire was connected. Do not connect the blue wire. Check to see if the jumper gets hot. If it does, there is a problem with the horn. Tom BRL 06-01-2023 @ 8:37 AM reply profile send p.m. New Member Posts: 102 Joined: Oct 2021 Hi Tom: OK thanks for the troubleshooting steps...I will do them and advise of the results in the next couple of days. Catfish Jones 06-01-2023 @ 2:13 PM reply profile send p.m. Member Posts: 37 Joined: Feb 2023 BRL Did I understand your write up correctly? You start hearing a low horn sound and the wire starts smoking even though you are not actively pushing the horn button? Was this the case both times it smoked? Steve 37RAGTOPMAN 06-01-2023 @ 3:13 PM reply profile send p.m. Senior Posts: 1958 Joined: Oct 2009 by your description sounds like you have a bad short, it may be the one horn is shorted out, remove the cover and check to see if you see something burnt or wire touching ground, ? dealing with bad wiring and corroded terminals/ will be hard to find the problem, you may have more then one sounds to me that you should install a new wiring harness, its not that hard, before you have a fire, I bought mine from RHODE ISLAND WIRING, came with very good instruction,and if you need help they are there to help you, hope this helps 37Ragtopman, Maine This message was edited by 37RAGTOPMAN on 6-1-23 @ 3:15 PM BRL 06-06-2023 @ 8:53 AM reply profile send p.m. New Member Posts: 102 Joined: Oct 2021 Hi Guys: Catfish: yes, the wire started smoking and one of the horns started a little bit after the smoking was already going on and all this happened without touching the horn button. This happened both times. The first time I had the horn assembly bolted into the car and the smoking started fairly quickly. The second time I had removed the horn assembly and just it propped up against the frame member when I did the test and it took a lot longer for the wire to start melting. 37Ragtopman: So my plan is to do all the electrical short tests that TomO has advised but I have been distracted by lawn mowing and general property maintenance since everything is growing so fast now. I have gone ahead and ordered another headlight harness, dash harness, and horn button rod wire repair kit from CW Moss and after I figure out where the short(s) are I am going to replace all these wires anyway...but I am going to replace that one burnt horn wire and do the short tests to figure out what is going on. The first time the wire burnt up I did take the horn assy off and pop off the back covers to see what was going on and the internals looked fine on both and the new pigtails I had put in looked perfect and the horns tested good when I applied a 6V test battery to them...but I have not looked at them yet after the 2nd burning. I also need to see if they are possibly shorted to chassis. I will advise you guys of my tests after I have finished mowing the lawns and trimming the trees. carcrazy 06-06-2023 @ 11:52 AM reply profile send p.m. Senior Posts: 1652 Joined: Oct 2009 You may have a short within the horn. BRL 06-08-2023 @ 8:11 PM reply profile send p.m. New Member Posts: 102 Joined: Oct 2021 Hi Guys: So I started my troubleshooting looking for a short. I started at the horn which had the burning yellow wire. I removed the back cover of the horn and inspected all the wiring, points, and stack-up of the insulator wafers...everything looked OK. When I ohmed both the yellow and blue pigtail wires together they showed continuity. Then, each pigtail wire was ohmed to the chassis of the horn and both showed continuity to the chassis. So, this appears to be where my problem is. What is surprising to me is that when I apply 6V across the blue and yellow wires, the horn works. When I apply 6V across the yellow wire and the chassis the horn DOES NOT work. When I apply 6V across the blue wire and the chassis the horn DOES work. Anyway, I guess tomorrow I will disassemble the points and all the insulator wafers and see where the short is occurring. This was a horn I bought on Ebay. My other horn works find and shows no continuity to ground with either the yellow and blue wire and only works between the two wires. So I am thinking this is my real problem. I will advise of what I discover on further disassembly of the horn. BRL 06-26-2023 @ 7:14 AM reply profile send p.m. New Member Posts: 102 Joined: Oct 2021 Hi Guys: I started troubleshooting the horn and the only place there could be a short was in the spacers and wafers for the points. So I disassembled the stack and inspected everything and could not tell where a short could possibly be. So after ohming everything out I carefully reassembled and there was no short. Horn tested good after points adjustment. I cannot tell exactly where the short was but it had to be in the spacer/insulator stack for the points...all the insulating wafers and mounting screw insulators were in good shape so I can only say that it must have been a mistake on my part in the initial assembly stack up. Anyway, I am going to say this was the cause of the burning horn wire and not do anymore investigating since I am replacing all wires including the dash harness and steering column horn wire. TomO 06-29-2023 @ 5:58 PM reply profile send p.m. Senior Posts: 7250 Joined: Oct 2009 I am glad that you found your problem and that it appears to be fixed. Tom

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