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 Investigation of a 12V Horn Relay - Inside and OutJump to page : 1 Now viewing page 1 [50 messages per page] | View previous thread :: View next thread |
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56D500boy |
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Expert 5K+ Posts: 9896      Location: Lower Mainland BC | . This past week I have been working on my 56 Dodge, fixing an issue with the turn signals. As I was sorting that out, I decided to fix what seemed to be an intermittent problem with my horns. As I got into that, I wondered whether the horn issue was actually a horn relay issue. I know how relays work and I have installed them on VWs and Audis for various lighting issues, e.g. fog lights on an 86 Jetta Carat and a high mounted third brake light on my 1994 Audi S4 wagon. However, I did not 100% know how the horn relay on the inner fender of my 56 Dodge worked. That led me down the path of figuring it all out. First thing was to examine the pertinent wiring diagram in the 56 Dodge Factory Service Manual (FSM). This one (now marked up with some of the supposed wire colours): My particular LA-built 56 Dodge has a mixture of coloured vinyl insulated wires and dirty difficult-to-determine-colour cloth covered/rubber insulated wires. So using the above diagram didn't really help me, especially since my car's horn really wasn't conveniently labeled with B, H, IGN and G like the diagram has. As a result, I had to get out and use my digital multi-meter (DMM) to ohm-out connections and/or check for 12V power - both non-switched and switched. In my case, the middle terminal had constant/non-switched 12V power coming in on a darker green vinyl insulated wire connected with a screw terminal to the relay. The other lighter green wire connected to a different screw terminal ohm'd out as the wire that went forward to the horns. The three wires on the threaded lug with ring connectors under a 3/8" nut were switched power. The final, 4th, terminal was switched power with a bullet connector on the end of a cloth-covered wire going towards and through the firewall. I assumed (turned out correctly) that it was the wire going to the horn switch at the steering wheel (more about that in another post to come (tomorrow?)). At that point, I didn't know whether the relay was good or bad and I had not found the diagnostic (which I found today), so I just swapped the wires onto a new aftermarket Niehoff horn relay that I had bought months ago to replace my original one (that looked like cr@p). The horn issue didn't go 100% away so I assumed that my original horn relay wasn't at fault. That was yesterday.  This morning, I got out my 56 Dodge FSM and found a diagram that I had never seen before in it or other FSMs that I have. It finally explained a lot: Since my original horn relay was off the car and I now knew what to expect inside, I opened it up a learned/confirmed a few things. The main one was I finally figured out that, of the three switched power wires that were connected to the threaded lug with ring connectors under a 3/8" nut, only one of the wires really had to do with the horn. The other two wires are just there because the factory needed a convenient connection point for switched power to things like the ignition coil. I also saw how the hot "B" (for Battery) terminal fed into the plate under the bottom of the relay coil and then up and around the coil to the points. And I saw how energizing the coil (by grounding the switch wire at the steering wheel) closes the points and directs battery power out the "H" terminal to the horns. I also confirmed that the cloth wire (in my case) with the bullet connector was the switched power wire that fed to the steering wheel horn switch (which grounds the current and energizes the coil) The following are photos of OE horn relay (Part Number (PN) 1626 929) before and after being opened, other 1626 929 (or similar) horn relays that are out there and finally my new Niehoff horn relay. Now that I know my original horn relay was fine, I might put some effort into stripping the paint off it and getting rid of the rust, etc. and then making it pretty and reinstalling it. We'll see. Enjoy.  Edited by 56D500boy 2021-01-24 5:53 AM (56DodgeOE1626929HornRelay_1_Annotated.jpg) (56DodgeOE1626929HornRelay_2.jpg) (NOS1626929HornRelay_Larger_Annotated.jpg) (OE1626929HornRelay_ExtractedFromItsShell.jpg) (OE1626929HornRelay_ExtractedFromItsShell_ShowingTheFourTerminals.jpg) (OE1626929HornRelay_ShowingMainComponents_Annotated.jpg) (OE1626929HornRelay_SwitchedPowerAndHornGroundWiresToFromRelayCoil.jpg) (EarlyStyleHornRelay.jpg) (AfterMarketNiehoff9dash33EquivalentToOE1626929_1.jpg) (AfterMarketNiehoff9dash33EquivalentToOE1626929_2.jpg) (AfterMarketNiehoff9dash33EquivalentToOE1626929_3_Annotated.jpg) Attachments ----------------  56DodgeOE1626929HornRelay_1_Annotated.jpg (176KB - 293 downloads) 56DodgeOE1626929HornRelay_2.jpg (137KB - 293 downloads) NOS1626929HornRelay_Larger_Annotated.jpg (155KB - 286 downloads) OE1626929HornRelay_ExtractedFromItsShell.jpg (92KB - 279 downloads) OE1626929HornRelay_ExtractedFromItsShell_ShowingTheFourTerminals.jpg (200KB - 284 downloads) OE1626929HornRelay_ShowingMainComponents_Annotated.jpg (169KB - 287 downloads) OE1626929HornRelay_SwitchedPowerAndHornGroundWiresToFromRelayCoil.jpg (230KB - 272 downloads) EarlyStyleHornRelay.jpg (50KB - 290 downloads) AfterMarketNiehoff9dash33EquivalentToOE1626929_1.jpg (207KB - 273 downloads) AfterMarketNiehoff9dash33EquivalentToOE1626929_2.jpg (221KB - 274 downloads) AfterMarketNiehoff9dash33EquivalentToOE1626929_3_Annotated.jpg (205KB - 291 downloads) | ||
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| Powerflite |
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Expert 5K+ Posts: 9648 Location: So. Cal | |||
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| 56D500boy |
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Expert 5K+ Posts: 9896 Location: Lower Mainland BC | Powerflite - 2021-01-24 10:05 AM Typically, there are two things that cause your horn to be intermittent. 1. Bad/rusty connections at the horn, including a decent ground connection to the horn body 2. Rusty internals on the horn itself. The first one is easy to fix, the second one is almost impossible other than replacing it. Been there. Fixed that. (So the horns are not the issue, it's upstream) http://www.forwardlook.net/forums/forums/thread-view.asp?tid=68724&... One of these suckers has new internals (the other is/was fine): Edited by 56D500boy 2021-01-24 1:58 PM | ||
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| 56D500boy |
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Expert 5K+ Posts: 9896 Location: Lower Mainland BC | . While looking for something else, I found this horn amperage draw in the 56 Chrysler FSM. 9 +/- 1 amps. That would be a lot to put through a simple switch. Best to have a relay involved. Hence the horn relay. Edited by 56D500boy 2021-01-24 6:12 PM (56ChryslerHornAmperageListing.jpg) Attachments ---------------- 56ChryslerHornAmperageListing.jpg (50KB - 285 downloads) | ||
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| samstrader |
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Extreme Veteran Posts: 443 Location: Beaumont TX | |||
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| 56D500boy |
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Expert 5K+ Posts: 9896 Location: Lower Mainland BC | samstrader - 2021-01-25 10:21 AM Thanks for the internal pictures Dave. Really makes it easy to understand. Agree. But I think that the horn relay from the 56 Dodge FSM really helped me the most. Once I saw that, I could see that the relay wasn't really anything special and that I was being confused by the extra wires feeding into/out of the switched power threaded stud IGN terminal. (That terminal was just used as convenient engine bay location to connect switched power to other devices, e.g. the ignition coil) Once I opened the relay, I could see that amount of current from the IGN stud terminal to the energizing coil must be tiny (because of the very small wires to and from the coil). I could also see that horn relay failure could be due to breakage of either of those two tiny wires, the wire of the energizing coil and/or the contact points. These failure modes are discussed in my subsequent 12V Horn Trouble Shooting post: http://www.forwardlook.net/forums/forums/thread-view.asp?tid=75319&... | ||
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| 56D500boy |
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Expert 5K+ Posts: 9896 Location: Lower Mainland BC | . Driving the 56 Dodge around today (Home Depot, the plating shop for the wiper pivots, propane, etc) when, out of the blue, as I approach a red light, the horns are on, FULL OOOOONNNN! I'm initially confused and try moving the horn ring (I've bumped it some how and it stuck on ????). Couldn't jump out at the light so when it goes green I go through and then park the car at the curb about 200 yds from the intersection. Horn BLARING the whole time.  Pop the hood (HORNS ARE REALLY BLARING!!!), trace the green wire back to the horn relay. Notice that the horn wire connection at the relay is leaned over toward the middle. HUH. Grab the connection and straighten it out (vertical), horns stop. HUH. So what happened was, apparently, I didn't tighten the screw enough on the horn wire terminal and, over time and vibration, the wire connector drifted over and contacted the adjacent terminal. MAYBE that wouldn't be a problem but it turns out that the middle terminal is the UNSWITCHED, ALWAYS HOT, terminal. OOoops. Lesson learned: Make sure your wire connections are: a) tight b) insulated better c) tight This photo is from above: The first photo below is approximately what I found when I popped the hood. The second was the 2nd "fix". Now I need to a) tighten and b) insulate better. Edited by 56D500boy 2022-04-29 6:07 PM (56DodgeHornRelay_HornWireAboutToShortToHotTerminal.jpg) (56DodgeHornRelay_AfterHornStuckOnFix.jpg) Attachments ---------------- 56DodgeHornRelay_HornWireAboutToShortToHotTerminal.jpg (172KB - 112 downloads) 56DodgeHornRelay_AfterHornStuckOnFix.jpg (169KB - 123 downloads) | ||
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