This is my first real post, so a little background. I bought a '68 XR-7 in July and have been working on it since then to get it back on the road. It had set outdoors for ~8 years. The PO had it running, but not very well. Body is sound except for front floorboards where a leaky windshield gasket soaked the carpet and caused some rust.
My first focus has been to get it running right and street legal so I can get it tagged. I’ve replaced just about everything on the brakes, new tires, new heater core and I’ve got it running better (still a little tweaking to do there). I finally have all the (exterior) lights working (even the sequential signals!).
It’s just down to the horns. The originals were bad, so I bought a pair of new aftermarket horns. They both test fine when I jump them directly to the battery. Pressing the horn button will light a test light with no problem, but it’s not pushing enough amperage to activate the horns. They make some feeble attempts and every now and then a week beep, but that’s about it. I’ve also noticed some intermittent sparking at the horn switch (at the steering wheel). I suspect bad contacts, but before I start to throw more new parts at it (I’ve given Don enough money already), I wanted to see if there’s anything I might have missed. Thanks in advance.
In the steering wheel there are two contact rings for the horn circuit. The turn signal switch has two spring loaded posts that ride on those contact rings in the steering wheel.
Also in the steering wheel there are two sets of contacts that can complete the circuit to the horn.
The contacts that allow the steering wheel to turn are supposed to be lubricated with white lithium grease. When the grease dries out, or someone changes the turn signal switch and does not replace the grease, those contacts get dirty and don’t pass enough current.
The two other sets of contacts in the steering wheel also get corroded and don’t work well.
Normally cleaning all of those contacts and applying fresh lithium grease to the sliders in the wheel will fix the problem.
Thanks Royce. I’ve replaced the turn signal switch, but didn’t clean horn contacts or lubricate anything. Looks like a good cleaning/greasing is in order. I’ll let you know how it goes. Thanks again.
Many times the female spade leads under the black plastic need re-crimping. They often get a tad rusty. Spray a little contact cleaner after removing the cover and re-crimp the leads.
I’ve taken the advice here and cleaned/greased the contacts at the switch, and I had already disassembled and cleaned the spade connectors at the horns. I found a great YouTube video by the NPD guys that takes you step by step through the trouble shooting procedure. It was on a '65 Mustang, but very similar to the Cougars. Here’s what I did/found:
Checked battery voltage and verified 12.7V.
Connected each horn directly to the battery with jumper wires to confirm that they both work. They do.
Removed the horn ring and checked voltage at the switch contacts. Found 12.6V there.
Jumpered the switch contacts and checked voltage at the horn spade connectors. Found 12.6V there as well.
Plugged the spade connectors to the horn and checked voltage (switch still jumpered). Found ~7.5V and no honk. Just the click/buzz I’d mentioned before.
Suspected bad grounds at the horns so I jumpered the ground connections directly to the batter negative post. Still ~7.5V and no honk.
So, I’m stumped. The horns work fine pulling 12.7V directly from the battery, but only click/buzz with 12.6V from the wiring harness. And they appear to be drawing about 5V in the process. Thoughts, ideas, suggestions? I’m at a loss. I’d really love to get this thing tagged and on the road with some nice weather left.
What you have documented is the meter is lying to you sometimes. This leads to troubleshooting results that are inconclusive or contradictory - or both.
The solution is to measure voltage across a load. A typical #1156 bulb with wires soldered to the contacts and alligator clips on the wires is a good load that can be easily connected in parallel with your meter for more reliable results.
When you load the circuit with the horns, it is showing you that there is too much resistance somewhere (probably at the slip rings or switch). The horns pull much higher current than the meter, so the meter measures Ok at the horn terminals, but the horns cause too much voltage drop across that resistance (about 5v in your case), and there isn’t enough voltage left (7.5v in your case) to operate the horns. You could measure the voltage going into the slip rings and horn switch while the horns are activated to see where the 5v loss is happening. That is where the problem will be.
When you load the circuit with the horns, it is showing you that there is too much resistance somewhere (probably at the slip rings or switch). The horns pull much higher current than the meter, so the meter measures Ok at the horn terminals, but the horns cause too much voltage drop across that resistance (about 5v in your case), and there isn’t enough voltage left (7.5v in your case) to operate the horns. You could measure the voltage going into the slip rings and horn switch while the horns are activated to see where the 5v loss is happening. That is where the problem will be.
For this reason, I prefer not to measure voltage but resistance along the wire path. Resistance will only change if there is a resistor wire in the circuit. The more connections you can include, the more accurate the resistance along the entire path will be measured. If you find more than 1.0 ohms, start disassembling the path, one section at a time, measuring resistance. When resistance drops to nominal, the last section removed contains the bad point. Re-crimp the pins, clean the corrosion, and test again.
Only once in the past 800 underdash harnesses did I find a wire that had completely disintegrated within the insulation without a break, probably a factory defect. Most problems are found in PO’s splices, factory pin crimps, and corrosion at the pins.
The two horns together draw about 7.5A at 12.5V, so even 1 ohm of resistance in the circuit would drop 7.5V leaving just 5V which isn’t enough to operate the horns. So if you are measuring ohms, you’ll need to be able to measure down into the tenths of ohms. It’s certainly a valid way to test, especially if you have experience doing it that way. But my cheap DVM doesn’t do it very well.
You always measure the highest voltage across the greatest resistance. Put your meter in the voltage mode and then measure voltage arcoss the connections. A perfect connection (no resistance) will read 0 volts. Most likely you are going to measure the highest voltage across the horn contacts. Or perhaps even between the horn body and ground (at the battery). Eventually you will find the high resistance connection.
High resistance upstream of the horns is what I was thinking as well.
I started from the steering wheel and tested resistance between the switch and each of the connections inside the passenger compartment (3 total). Each one tested at ~0.2 ohms individually, and I got the same reading checking from the switch to the last of the three connections. According to the schematics, there shouldn’t be any more connectors until I get to the horns, so I suspect a problem with that section of wire. My DVM doesn’t have long enough leads to reach from the switch to the horns, but maybe it’s ok to add some length to one of the test leads?
Unfortunately, that harness is wrapped in tape and pretty tough to access. I’m thinking about bypassing the harness with a new wire from the last connection in the cab out to the horns to see if that gets it.
Thanks for all the input. I think with a little guidance, I’ll eventually get it.
Be sure and also check across the horn switch itself with horn activated. But you won’t be able to accurately measure ohms if current is flowing through the circuit, so you’ll need to either disconnect the battery or measure voltage drop instead.
If you have battery jumper cables, those can be added to each DVM lead to increase length without adding any significant resistance.
My advice that resistance readings should be 1 ohm or less was intended for the average hobbyist and typical quality DVM’s. Some DVM’s allow tare corrections, which should lower resistance readings below the 1 ohm nominal value. Probe placement and a good contact should also lessen a resistance reading. Trying to obtain 0.1 to 0.2 ohm readings is difficult (but not impossible) for most people and meters. For a quick and dirty reading, the 1 ohm value is adequate; most times bad resistance yields values in the 10’s to 100’s ohms.
I should go ahead an put a bow around this in case someone else has the same issue. After removing and reinstalling the steering wheel three or four times, cleaning, lubing, testing the switch, I wasn’t able be correct the issue. I still suspected the switch since I was getting what I thought was good readings everywhere else.
I finally gave up and installed a relay as suggested above. With this set up, the horn switch becomes the ground instead of power supply. It instantly solved the problem, and I now have nice loud horns every time.
Thanks to everyone for your input and suggestions. I’ll call this one solved.
looked at this for my issue, but I don’t think its the same. Figured I’d keep horn questions in the same thread.
I restored my rim blow horn using the WCCC repro two winters ago. The dual horns had worked fine since. Recently I was in a parade with a lot of horn blowing. Towards the end they started to “fade”. When the parade ended I checked and they were both quiet.
I tested them via battery to horn no sound on either horn. So my simple thought is need 2 new horns. But… both going at the same time seems like I may be missing something.
As an aside, where the hell is the fusebox in a 69?
