Horn wiring problem

jjanari · Dec 28, 2013

Hi,

I apologize for the long post. Please note that I know very little about automotive electronics, so bear with me.

I'm having a problem getting my horn to sound with the turn signal switch. both horns are brand new and bench tested, so I know they work. The fuse appears intact.

Originally, I thought it was the horn pad contacts since they were very worn. however, I replaced them and no luck. When I jumper the two spring loaded switches, the horn won't sound. (see attached picture).

However, when I put my jumper wire to the spring loaded switch with the yellow/blue striped wire and ground the other end to the steering column's housing, the horns sound. (see attached pic)

Note that the entire wiring harness was replaced a few weeks ago and, prior to that, the horn worked. I spoke to the mechanic who did the rewiring and he told me to get a new turn signal switch, which I did. Note that I have not installed the new turn signal switch into the column or removed the old one; instead, I simply unplugged the old switch and plugged in the new one; however, when I went to jumper the two spring-loaded switches, still no horn. again, I did not install the turn sig switch assembly into the column, but would think that jumpering the two switches would make the horn sound, if this makes any sense. Any ideas?

sorry, the 2nd picture didn't seem to post. the horn sounds when I put my jumper wire to the spring-loaded switch (with the yellow/blue striped wire) with the other end to the metal steering column:

Don C · Dec 28, 2013

It sounds like you have after market horns with a horn relay. The horn button provides a path to ground for the horn relay. The wire that runs to the horn relay is good, but the wire that provides the ground isn't.

jjanari · Dec 28, 2013

It sounds like you have after market horns with a horn relay. The horn button provides a path to ground for the horn relay. The wire that runs to the horn relay is good, but the wire that provides the ground isn't.

thanks for the reply. the replacement horns are the same as stock. as far as I know, the mechanic re-wired the car using the wiring diagram for a '73 mustang; per the diagram, there is no "horn relay," at least not one that I see.

midlife · Dec 28, 2013

OK, here's how things are "supposed" to work. Power is routed through the yellow/blue wire and the horn switch then transfers power to the blue/black wire out to the two horns. The horns accept the power so long as they are grounded to the chassis. Jumpering the two posts on the steering column accomplishes the same thing as pushing on the horn switch on the steering wheel.

By grounding the voltage at the yellow/blue wire to the chassis at the steering column should cause a massive electrical short in the yellow/blue wire, but that isn't happening. I thought that the yellow/blue wire and the blue wire were switched at the connector, but that would only ground the outgoing signal and not provide voltage. However, if your chassis is not properly grounded, there could be voltage at the horn bolts and grounding the incoming horn signal would cause the horns to blow. You can test this by measuring voltage at the horn bolts relative to battery ground. I'd then test the voltage at the signal tabs relative to battery ground with and without jumpering the two posts on the steering column.

I'd also test the horns in place by jumpering battery voltage to the tabs where the wires slip on.

A most peculiar problem. As someone else said, if there is a relay for horns somewhere, then its possible that the relay is set up incorrectly.

jjanari · Dec 28, 2013

OK, here's how things are "supposed" to work. Power is routed through the yellow/blue wire and the horn switch then transfers power to the blue/black wire out to the two horns. The horns accept the power so long as they are grounded to the chassis. Jumpering the two posts on the steering column accomplishes the same thing as pushing on the horn switch on the steering wheel.

By grounding the voltage at the yellow/blue wire to the chassis at the steering column should cause a massive electrical short in the yellow/blue wire, but that isn't happening. I thought that the yellow/blue wire and the blue wire were switched at the connector, but that would only ground the outgoing signal and not provide voltage. However, if your chassis is not properly grounded, there could be voltage at the horn bolts and grounding the incoming horn signal would cause the horns to blow. You can test this by measuring voltage at the horn bolts relative to battery ground. I'd then test the voltage at the signal tabs relative to battery ground with and without jumpering the two posts on the steering column.

I'd also test the horns in place by jumpering battery voltage to the tabs where the wires slip on.

A most peculiar problem. As someone else said, if there is a relay for horns somewhere, then its possible that the relay is set up incorrectly.

thanks. a few clarifications on your points:

1) when you say to measure voltage at the horn bolts relative to battery ground, can you walk me through how I would do that with my multimeter? by horn bolts, do you mean the single bolt holding each horn to the firewall?

2) again, using the multimeter, how would I test the voltage at the signal tabs "relative to ground?"

3) per your suggestion, I did test the horns in place by applying battery voltage directly to the tabs on the horns themselves and both sounded.

I appreciate your time and patience!

midlife · Dec 28, 2013

1. Set the meter to DC Volts Set one probe tip on the bolt holding the horn to the chassis and the other probe tip to the negative side of the battery. You should see less than 0.005 Volts.

2. Same as 1, only the probe goes to the wire (female spade) that slides over the horn male spade (I was wrong above). You want to measure the voltage going to the horn. Voltage should be very low (<0.1 volts) with the horn switch open and 12V when the switch is closed (jumpered). If in between, you have bad contacts at the female spades that slide over the horn tabs. I see that a lot.

I still say that based upon grounding the incoming horn power to the turn signal switch, you shouldn't be able to get the horns to blow. Something is very wrong. Check again which wire you are shorting.

jjanari · Dec 29, 2013

1. Set the meter to DC Volts Set one probe tip on the bolt holding the horn to the chassis and the other probe tip to the negative side of the battery. You should see less than 0.005 Volts.

**yes, I see less than .005 volts.

2. Same as 1, only the probe goes to the wire (female spade) that slides over the horn male spade (I was wrong above). You want to measure the voltage going to the horn. Voltage should be very low (<0.1 volts) with the horn switch open and 12V when the switch is closed (jumpered). If in between, you have bad contacts at the female spades that slide over the horn tabs. I see that a lot.

***I am not getting 12V with the switch jumpered??? I don't see how this can be if I can get the horns to sound by grounding the one horn switch to the steering column.

I still say that based upon grounding the incoming horn power to the turn signal switch, you shouldn't be able to get the horns to blow. Something is very wrong. Check again which wire you are shorting.

*** I'm fairly certain it's the yellow/blue wire I'm shorting.

I'm curious regarding your thoughts. However, at this point, I am planning to take the car back to the mechanic.

Midlife, I really appreciate the time you've spent helping me. while I could have easily returned to the mechanic when the problem first arose, I wanted to at least try and diagnose it or even fix it myself. My plan is to post a solution to the problem once it's resolved.

-Jimmy

midlife · Dec 29, 2013

1. Set the meter to DC Volts Set one probe tip on the bolt holding the horn to the chassis and the other probe tip to the negative side of the battery. You should see less than 0.005 Volts.

**yes, I see less than .005 volts.

2. Same as 1, only the probe goes to the wire (female spade) that slides over the horn male spade (I was wrong above). You want to measure the voltage going to the horn. Voltage should be very low (<0.1 volts) with the horn switch open and 12V when the switch is closed (jumpered). If in between, you have bad contacts at the female spades that slide over the horn tabs. I see that a lot.

***I am not getting 12V with the switch jumpered??? I don't see how this can be if I can get the horns to sound by grounding the one horn switch to the steering column. I don't either...that's what is puzzling. Your wiring is not correct according to the factory---that's the only explanation.

I still say that based upon grounding the incoming horn power to the turn signal switch, you shouldn't be able to get the horns to blow. Something is very wrong. Check again which wire you are shorting.

Click to expand...

*** I'm fairly certain it's the yellow/blue wire I'm shorting.

I'm curious regarding your thoughts. However, at this point, I am planning to take the car back to the mechanic.

Midlife, I really appreciate the time you've spent helping me. while I could have easily returned to the mechanic when the problem first arose, I wanted to at least try and diagnose it or even fix it myself. My plan is to post a solution to the problem once it's resolved.

-Jimmy

joe71 · May 31, 2014

Jimmy,

Were you able to resolve this issue? I am having the same problem.

Thanks in advance.

---

Joe

ForSaleNo · May 31, 2014

My horn has two problems: 1. when I press for it, it don't sound off, I have to feel around to find that spot to make it work

2. when my horn does sound I either have to low sound or the high sound if I find that spot then they both sound..was this your problem too?

OMS · May 31, 2014

My horn has two problems: 1. when I press for it, it don't sound off, I have to feel around to find that spot to make it work

2. when my horn does sound I either have to low sound or the high sound if I find that spot then they both sound..was this your problem too?

Forsaleno...

Your problem is a broken horn switch

Don

Item #D2AZ-13875

70-73 STEERING WHEEL HORN SWITCH ASSEMBLY

Two spoke steering wheel horn blow switch assembly. Two special pressure switches with connection terminals installed into black plastic frame. Reproduction. Price: $79.95

Horn wiring problem

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