Horn relays blowing up ?

[Deschodt]

I was hoping someone could suggest a likely cause for this...

I have an 83 with a single horn replacing the 2 tone one (right there that could be an issue, not 100% sure of its draw and what the limit is), and also a Momo wheel (shouldn't matter but for the sake of giving all the info).

I hooked up the horn and it worked fine in the garage, once anyway... A few days later, trying to use it on the street, nothing... Once home I can hear the horn relay "click" when I press the horn button, but no horn... Replaced the relay with a spare, "Beeep". Ok, though that was it, but 2 days later, almost the same story, got a little "meep" for 1/2 a second and then nothing, just a click of the relay again...

Am I blowing up relays ? (they're not cheap) Any ideas what could cause that? That horn is a replacement for a 12v 356 horn so I think it should be OK ! Any common things I can check ?

[pozee]

You may have a short/ground problem. Check the wiring. What did you do with the wiring to the second horn?

[pozee]

By the way - is the amp. draw the same on the replacement horn as the two it replaced?

[Deschodt]

I forgot about the second horn, because it had been removed from my car a long time ago (interfering with some home made air ducting to the cooler). The wires are just snipped and insulated, but that had been like that for years. I don't know about the draw, actually, I never suspected it'd be an issue but you could be right. No idea how I'm gonna find out though !

PS: is a clicking relay a sure sign it's dead then ?

[ChkbookMechanic]

A clicking relay means it is working.

I'd check the wiring and make sure everything is connected securely then get a voltmeter and make sure you are getting 12V to the horn.

[Joe V]

A clicking relay doesn't necessarily mean that it is working if the contacts are burned out. I had a similar situation where the horn relay would last less and less until I could only get 1 short beep out of them. I ripped out the factory trumpets and installed a pair of salvage yard BMW 7 series horns. Now my relay is happy, and I can toot whenever I want.

Below is a picture of one of my many (about 5) smoked relays.

[911pcars]

Originally Posted by Joe V

A clicking relay doesn't necessarily mean that it is working if the contacts are burned out. I had a similar situation where the horn relay would last less and less until I could only get 1 short beep out of them. I ripped out the factory trumpets and installed a pair of salvage yard BMW 7 series horns. Now my relay is happy, and I can toot whenever I want.

Below is a picture of one of my many (about 5) smoked relays.

This is a classic symptom of excessive current through the power circuit of the relay. In the case of the horn circuit, check the horn circuit continuity (continuity only to the ground wire, not the housing) and the wires from the relay to the horn. Perhaps another Porscha circuit in need of a fuse.

Sherwood

[ChkbookMechanic]

Originally Posted by Joe V

A clicking relay doesn't necessarily mean that it is working if the contacts are burned out. I had a similar situation where the horn relay would last less and less until I could only get 1 short beep out of them. I ripped out the factory trumpets and installed a pair of salvage yard BMW 7 series horns. Now my relay is happy, and I can toot whenever I want.

Below is a picture of one of my many (about 5) smoked relays.

True, I forgot about it burning its contacts (hasn't happened to me just yet).

But normally swapping relays around for circuits you know work should with ones that aren't normal show pretty quickly if it is the relay or the circuit that is having the issue.

[dshepp806]

...or measure the current that those babies' are pulling...clearly a load issue. Swapping another relay in will eventually provide the same failed results, as the contacts go through their (repeated) overcurrent conditions from an overcurrent draw from the load. The only "quickness" you will get will be failure of the "new" relay (or it will provide sufficient conductivity for the horn to burn out.

All of the previous relating to horn(s)...as the culprit

This is assuming there exists no "other" influential overcurrent culprits (having nothing to do with a horn going south), as Sherwood has alluded to.


Best of luck,

Doyle

[Deschodt]

Well, I opened the existing "clicking only" relay, and while it does not look anything as bad as the pictures above, there is a little discoloration in the exact same spot. So it's probably too much draw... just not quite as catastrophic...

The continuity from the horn wires is maybe a problem.... I have continuity from 3 of the relay terminals on the fuse box (86 87 and 30) to.... both wires at the horn... Does that make sense, relay off? Both ? I then did a continuity test from both wire ends to the ground, both beeped, so they are both grounded ? That's probably it...right?

I removed and researched the horn, it's a Hella 300 hz, and apparently it draws 72 W ! Is that too much for a puny relay then ? What's the max allowable ?

Last thing, I swapped my bad "clicking only" relay with the "good" fuel pump one, got another "BEEP" of a good horn by only tapping the button briefly so as not to burn that one as well... So the wiring is good in asmuch as it connects the right bits to each other, but the continuity issue above is bad if I understood this..... I put the "bad" relay to the fuel pump, and got no fuel pump noise, so toasted realy for sure (my pump is wired so as to run with the ignition ON, another issue, I know, but actually that oddity has helped me troubleshoot many things so far)...

I put the fuel pump relay back on and I had thankfully not burned it, although I will for sure replace it and put it back on the horn circuit instead when our host delivers my latest order ;-)

Anybody knows the draw of a porsche horn then? All I know is hella 300hz, 72W, 12V, serial 005631, sold to me as a valid replacement for older porsches.... Now I have to figure out why the power black wire is grounded, seems to come from the headlight bucket...

[ossiblue]

Your horn's draw is in amps, not watts. Amps=watts/volts so your horn should draw 6 amps, max. The relay should handle the amps too, but if it is burned then you have excessive draw as you suspect. Try putting an ammeter on the circuit, ground the horn, and read the draw.

edit: Don't know the circuitry on an 83, but on earlier cars, there is no fuse in the hot lead to the horn--it is a direct connection from the hot side of fuse #2 (circuit 30) to the relay. If your set up is similar, then your relay is acting like the fuse and probably the horn is defective and drawing too many amps blowing the contacts.

[Joe V]

Greg,

Here's a horn diagram for an 84. Can anyone confirm changes, if any, from 83?
Hope this helps.



Ossiblue is right. Since the circuit has no fuse, the relay then becomes your $20 circuit breaker. It might save you a ton of $$ to buy (or make) an inexpensive inline fuse to help in the diagnosis of your problem.
If you can't find one locally, drop me a PM, and I'll mail you one....WAIT A MINUTE! You're down the street from me! Just give me a call and we'll figure it out. 813-205-7358. I'll be playing Santa later today with the nieces, so the wife unit and I will be in Tampa.

Regards,

[Deschodt]

Joe, thanks a lot, very kind of you to offer! I may not be home until late today, though, and then it's Xmas... so maybe this w/e ?

I'm no electrical genius, but from the diagram, it's not right that I should get continuity from the fuse box to BOTH horn wires and that the power wire to the horn appears to be grounded, right ?

Just want to make sur eI'm on the right track, and it'snot a consequence of not having a good relay in !

[Joe V]

Greg,

I'll be tied up shooting a wedding Sat evening, but either earlier in the day or Sunday (just about all day) would work for me.

Merry Christmas!

[dshepp806]

start disconnecting things until you find "where" this ground is being (mal)sourced from..


Best,

Doyle

[911pcars]

Greg writes:
"I'm no electrical genius, but from the diagram, it's not right that I should get continuity from the fuse box to BOTH horn wires and that the power wire to the horn appears to be grounded, right ?"

So that everyone is on the same page, the control circuit is on the left side of the horn relay schematic (86>85>horn contact>ground); the power circuit is on the right side (30>87>horn>ground.

When the horn button (contact) is depressed, that completes the control circuit. The relay becomes energized and causes the contacts in the power circuit to close (30>87). This allows current to to flow from the battery to the load (horn), then to ground which completes the electrical circuit. The result should be beeeeeeep (horn SFX). Electrical loads such as horns, motors, bulbs, heating elements, etc. are designed to draw only so much current to operate correctly.

In your case, there's an abnormal current path to ground that partially or completely bypasses the load and thus draws excessive current through the circuit. That "short circuit" is either in the circuit path between the relay and the horn(s) (terminal 87, Blk wire) or inside one of the horn units.

To clarify my earlier post about checking continuity, there should be no continuity (no path) between the horn source connector and the horn housing. If so, that indicates an internal short and perhaps the cause of the burned relay contacts. In the case of a Porsche horn, the circuit is grounded via a dedicated ground wire. With other manufacturer's horns, the metal housing itself may be the ground path.

Sherwood

[Deschodt]

Problem solved... I am such an idiot !

When I backdated the car, I had to install brand new turn signal boxes in the long hood fenders, and somehow, the ground of the passenger side turn signal ended up going to the power side of my horn, instead of the ground side... No idea how, why, on what planet, but I'm actually surprised I pulled off a backdate without burning the car to the ground, so live and learn !

Strong horn, no burned relay, and possibly less blown turn signal bulbs too !

[dshepp806]

yes,...electrical quiesence (and less chance of burning something completely up).....

Congrats!!

Best,

Doyle