Horn and rear fog light issues

I'm prepering my ex-girlfriend's Mk1 GTi convertible for it's MOT - and it's giving me some major headaches!

First and most important is the horn.

The guide in the FAQ about the horn is no good - this car has the late model fuse box (no additional relays), but the horn guide in there says Relay 4 is the horn relay - whereas the fusebox guide says relay 6 is the horn.

There is no continuity from relay 6 (any pin) to the horn wire under the steering column.

The horn push works (I removed the wheel) but the centre of the column is not earthed, so it doesn't work - can anyone tell me where the column is earthed? Once I get that figured out I can build a new horn system with a new relay and horn.

As for the rear fogs - I checked the fuse (above relay 5) and all the other fuses, but still no rear fogs. Any suggestions here? This one's less important, as I can build it from scratch, it's just the telltale light that's required for the MOT that's a pain.

Maybe I'm just trying to save my fingers or maybe I'm just lazy, but for me there are two things that would help get things started and narrowed a little. Is there battery power at the wire in the steering wheel when the key is switched on? Is there battery power at the rear tail light, fog light wire or socket, when the key is on - lights switched on to low beam and fog light switch pushed to position two?

There should NEVER be battery power at the wire in the steering wheel - unless you're trying to start a fire!

It works by grounding the wire, to close a relay - the other half of the relay works the horn (as it's too high a current for the horn push usually).

As for the fog light - no, there's no power at the switch - the telltale light doesn't come on in the switch.

I'm more bothered about the horn push though.

the column is earthed in the engine bay, there is a wee wire from steering rack to the chassis

the fog light gets power from the headlight switch, check pin 83 on switch gets power with lights on, grey/yellow wire. this gets power from pin 56 on hl switch, white/black wire.  (this is from MK2 haynes pre-90, so might not be right but I believe pin numbers/wires didnt change between late cab and pre-90 mk2)

Yeti1 said

There should NEVER be battery power at the wire in the steering wheel - unless you're trying to start a fire!

I guess this is a case of call it like you will, but for me 12+ volts is battery power. Stick a multi-meter to the wire at the horn switch and turn the ignition on, bet you get at least 12v, I always do. So if battery power causes you to think it is direct from the battery then call it something else if you like. But yes, that "voltage" closes a relay which completes a second curcuit which uses power direct from the battery to sound the horn.

this link may help a bit re the horn problem, the column earth wire is brown…

http://www.vwgolfmk1.org.uk/modules.php?name=Forums&file=viewtopic&t=41833&highlight=horn

the horn connection isnt 12v, its an earth as said.  One look at the wiring diagrams proove it, plus I know this for a fact as I have myself earthed the horn contact to the column with a screwdriver to check everything works without a wheel fitted.  If it was 12v then I would have made a short circuit thru my screwdriver and melted something, since as I said above the column is earthed to the chassis!

The horns themselves get permanent 12v, and are earthed thru the steering wheel. in the case of gti twin horns, they're earthed via a relay, low spec models have a jumper wire across the pins in the relay socket.

Lord knows I hate getting into discussions like this, but unless someone else jumps in and says ?Hey, I just checked and there is 12V at that wire? then I guess I have to. I would hate to have the entire Volkswagen community remain in the darkness just because nobody will take the time to test a wire.

The wiring diagrams VW uses and many of the manuals like Bentley (most there are from VW) are better described as flow diagrams. The power for a component starts at the top and flows down to the ground (earth) where it finds it's way back to the battery. Due to the complex wiring of some systems the path the electricity takes can cover many pages of the diagram. But the final destination of the power is always at the bottom of the page where is either returns to the battery directly or through the chassis.

For the horns, with or without a relay the grounding point is the steering column. The flow diagram shows this with a circled number (13 I believe) and looking up the number will tell you the location is the steering rack, that tiny wire really. Now this whole thing could be just a terminology issue but I can?t tell from your post. Yes, the wire is a path to ground, even though the wire color code is red/? and not brown/?, but every wire in a circuit from the power source to the point where it returns to that source is a ?ground path? if you want to call it that. Fact is, the voltage is there just waiting for the path to be complete by pressing the horn button which sends it through the steering column on it?s way back to the battery, just like most electronic fuel injectors. You say that you shorted it with a screwdriver and didn?t get a spark, fine you had luck. I have shorted that wire many times on many cars by mistake and got some nice sparks and black marks inside the steering wheel. One time it shorted agains my wedding ring and the steering wheel and burned a ring around my finger. I believe that if I were to hold the wire to metal with the key switched on it would cause a fire in the wiring if it were not for the fuse which blows when it happens. I test the power at the wire often when troubleshooting horn problems and always get 12 volts or the test light lights. It should be that way as the power comes from the ignition circuit (marked 15 at the top of the flow diagrams).

Think of it this way. Remove the heavy black wire from your battery, the ?ground wire? and place a test light or meter between the wire and the battery negative terminal. Now turn something on which draws power, turning the ignition key is fine. Does the light light or meter read 12 volts? Of course it does as the returning voltage is passing through the test light or meter. ?Ground wire? is just a term used to indicate the last wire in a circuit that the electricity passes through on it?s way back to the battery. It does not mean that power is not present in the wire if you make a mistake and touch it to some metal chassis part. Yes the diagram shows it as leading down to the bottom of the page where it grounds, all wiring does at some point, but I would not touch my tongue to it and turn the ignition on!

the difference is its an earth path, not a live/ign live feed.

think of it this way, if it was just a live or ign live and you earthed it, what you have is a short circuit.  since its an earth path, the worst that will happen if you earth it is the horn will be stuck on.
Try the same thing with say the chunky live wire from the ign switch = fire.

edit: what I'm trying to say here is 'battery power' to me at least implys its a direct feed from the battery, though I see to you it just means '12v'. I assume Yeti1 thought the same as me from his 'fire' comment, this would suggest the column pin is wired direct to the battery, which would be bad

It is actually simple…

The horn contact connects ground (earth) from the steering collum/rack, to one side of the horn relay. The other side of the horn relay, is connected to +12V.

So, the wire(s) in the steering wheel is NOT in any way conected to +12VDC. You would get a short circuit if it were!

The reasons for the sparks - if you short to the steering collum with e.g. a screw driver - is because you are making an electrical circuit, i.e. connecting the ground side of the horn relay and thereby drawing current.

If you take a meter and measure between the horn wire and the steering collum, you will get 0V. If you get +12V, you have a serious problem with your wiring.

Try a new foglight switch, 5 more available before they are obsolete from VW UK!

If not Mk2 Polos in scrappys have the same switch..

I must say I was really getting ready to pack it in on this one and let people believe what they will, which they seem to do most times anyway, when I started doing some cleaning in the garage to paint. While moving some parts around it hit me like a ton of bricks, "Different steering wheels!" So in a last ditch attempt to get everyone on the same sheet of music as they say, I bow to the fact that I didn't think or cover more then one type of steering wheel when posting.

There are a few different steering wheels used by VW and "aftermarket" companies. Some have internal horn switches and some have external switches. That is, some horn switches are built into the steering wheel with internal wiring and some have external wiring and switches. This I believe is where the problem between the wire being "hot" or not lies. I was thinking and therefore posting about one type of steering wheel while others were thinking and responding about another kind. As an example, the 4 button VW GTi wheel I think is an internal type and therefore the wire comming off it inside the column is the lead from the "ground side" of the horn switch. It will connect directly to the chassis through the column and no power will be there until the button(s) are pushed. On steering wheels like the three spoke aluminum one used on some Golf1 and Scirocco models, the switch is external and the wire under it is live when the key is on. This type grounds direct to the wheel/column via metal to metal contact. The internal kind has to be removed and tested for power at the small brass finger which contacts the slip ring, or remove the connector and test there.

So I guess you can fault me if you like for not thinking or covering all types of VW and aftermarket steering wheels, I can live with that even if it's not really all my fault. But if you deny that different types of steering wheels due change matters and the wire could just be live with the key on, then I guess there really is no hope left.