Need help with a horn problem

Hello everyone,

I’m posting this thread, hoping someone could help with my horn issue. I have a 1985 308 GTS QV (US Car) which a while ago, I removed the entire horn assembly when I proceeded with my restoration project, however it worked just fine prior to the dismantling of it. Just recently I reinstalled the horn assembly back into the car, in which IMO this is a very simple straight forward system as I thought!!! So, now when I push the horn button, the compressor is functioning but instead of that sweet high pitch European sound, it just makes a low growing sound. I did a few things to find a root cause. First thing, I did, I searched within the 308 section for clues about the horn and compressor and found lots of older threads with great stuff, but nothing comes close to my problem which is why I’m reaching out to you all.

So… months ago, prior to the reinstall, I tore apart the compressor to restore it back to new again, It was in terrible shape, visually... I yellow zinc the middle section of the compressor, repainted the housing and reassemble the electric motor, lubed with oil the thin veins that rotate inside the compressor housing that makes the horn sound prior to completing the reassembly phase.

After, hearing this awful sound, I thought I had the two tubes connected up wrong to the compressor but no that’s not the problem, I had them right. I then thought it was the trumpets that was the problem, but they both worked when I applied compressed air from my portable air compressor to the outlet tube, and they both work just fine, nice and loud! … so scratch that off the list. I then though I messed up and damaged the compressor. So this past week, I found an identical new FIAMM compressor replacement (12V) on ebay for a decent price. When I received it, I quickly installed it hoping to hear that loud horn sound... which wasn't the case, after I pressed the horn button again, it made the identical low growing sound just like the old one did. So now I’m puzzled to “why” it’s doing this and what I’m doing wrong??? Could it be a voltage issue???? But its connected to a new battery inside the car

Rob

 

Check out the grounding.

 

Check... This is how its currently is... Does anyone see something wrong??? This is how the original grounding wire was when it was working...

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What volts are you getting at the compressor terminal, if you are getting less than 12 it may be your issue. Try connecting compressor across the battery to test it.
Does the compressor rotor have a few slots in it, to which is fitted some Tufnell vanes ( light brown fiber boards)

 

If you are going to leave the ground wire like that, make sure the bracket bolts to a clean metal surface. Personally, I would change that ground wire to one with a larger ring terminal that attaches to the body with the bracket bolt/stud.

 

Stay tuned... I'll give this a try over the weekend... thx for the suggestion!

 

Over the weekend, I did some diagnostics of the horn problem, however the issue hasn't been identified just yet. I now have removed the horn compressor for a total of six times. I took "bitsobrits" suggestion and I attached a new connector and re-routed the ground wire between the bracket and touching the frame. I removed some of the paint and finish from prior to mounting it as shown in the following pics, still the problem didn't' go away. I then connect the power wire to my meter, while pushing the horn button on the steering wheel, I'm getting good voltage to the compressor. I even used WD40 and lubed the inside of the replacement compressor, nope no dice!!!!

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First, you should own a power probe. This device allows you to put 12 volts directly into the compressor. This lets you immediately know if you are dealing with an electrical issue or not. This tool will also tell you if you have enough voltage or a bad ground.

Secondly, for $20 on amazon you can buy a knock of compressor and trumpet. Bench test it first just to make sure the $20 unit works. Then hook the trumped and hose to your installed compressor and see if you get the appropriate sound level. If you do then you immediately know the issue is either a kinked hose or a bad trumpet. If you don't then you have a bad compressor. Install the $20 compressor and you are done.

 

Did you make this voltage measurement with the compressor motor still connected to the leads? The circuit has to be "under load" to get a meaningful voltage measurement. Just measuring the disconnected leads can detect an open circuit (infinite resistance), but it can't detect an unwanted non-infinite resistance somewhere.

 

Thanks Steve... I'll check this again using your suggestion... thx

 

Did you test the horn assembly directly with temporary wiring to the battery to make sure it works as it should and eliminate/identify either power supply or grounding issues?

 

Yep... I did.... used a 12V battery... it worked just like it did when it was mounted inside the car... but no horn sound through

 

This coming long weekend, I'll re-test the trumpets again.. and retrace the hose for kinks.. I need to remove the grill again! Stay tuned!!!!

 

I have the same problem you have.

You can test the trumpets by disconnecting the air hose from the compressor and blowing air from your shop air compressor into the hose.

Disconnecting the 12v power wire at the compressor and measuring the voltage coming to the compressor when the horn button is pressed shows whether the compressor is getting sufficient voltage.

You can test if the compressor is getting sufficient power by connecting the compressor directly to a strong 12v source (such as the car battery via a couple of wires) and seeing if that makes the trumpets work.

You replaced the compressor with a new FIAM (as did I). So that really should eliminate the compressor as the problem in the first place.

I got good noise from the trumpets with my shop air compressor. My FIAM compressor(s) blew good air. I can't help but wonder if the trumpet reeds have corroded (or something) and now are so stiff that they require more air than the car's air compressor can provide.

Ultimately, I just gave up and installed Hella SuperTones behind the battery with a relay (and fuse) directly from the battery and triggered by the horn button. I can switch back to the factory horn by simply moving the trigger wire. I do get a weak bleat from the airhorns when I supply power to the compressor.

 

Just for giggles, pour rubbing alcohol into the compressor and run it a bit (Not connected to the horns). If you see crud coming out repeat the process until there is nothing but clean alcohol coming out. I may be wrong but lubricating the vanes may be allowing air to escape rather than be compressed. This was the case in some technical equipment I used in another lifetime and in the Judson Supercharger. Old tech, simple but doesn't need lubrication other than the bearings.

YMMV

 

I disagree. With no load on a circuit the wires will show battery voltage and hide bad connections. But under load the real circuit voltage will show up. Measure voltage at the motor while it is running (press the horn button) and see what it is.

I have exactly this same issue, and I think I'm at the same stage you guys are. With my shop compressor the horns are loud and clear. I replaced my pump with another pump but my horns are still pathetic. I have not yet cared enough to troubleshoot further. But I suspect this is like the power windows where all those connections over time have gotten a bit more resistive and it adds up to sad horns.