Anyone got something they would like me to talk about?
How to trace a circuit. The problem with my horn (fnarr) is annoying me, I've got a button on the steering wheel, that seems to create a circuit with a metal ring in the boss, which then goes
somewhere into the connectors at the top of the steering column. It then disappears into a mass of wires under the dash, before the fuse box, then disappears into another mass of wires and ultimately ends up as a single wire going to the horn. I have no idea where along this selection I may have issues, I don't even really know if I'm looking at the right connectors on the steering column.
Things I know : I have two connectors that go to a switch which when I flip it turn the horn on. I have one connector on the steering column for the horn as far as I can see. It used to run through a relay, but now doesn't (the switch was a temporary fix for a broken relay about six years ago).
Any ideas of the best way to approach this in a set by set manner. I have a multi meter and little idea how to best use it on car electrics.
So that one is straight forward. Your horn will go to the switch. The other side of that switch is a live. Flick switch, horn beeps.
Now. Normally with a horn, one of two configurations are used:
1) used where there's a tube over your steering shaft, and the tube is isolated from the ground (chassis). The horn has two cables going to it, a live and a ground. Live live is permanently live, fed from your fuse box, and the ground connects to your steering column cover (which is isolated from earth). You press your horn button, this connects your steering shaft (which grounds to your chassis via the steering box) to the cover, via your steering boss, and so your horn now has a path to earth and it beeps.
2) The horn has one cable going to it, a switched live, which is switched usually by a relay, and grounds to your chassis via the mounting bolt on the horn. Your horn button usually closes the earth on the other side of the relay by grounding it to your steering shaft, which causes the relay to close, and activates your horn.
You have the second type. The switch you describe is doing the job of the relay.
So, some questions:
Your relay, is it still present? Has it been replaced for a working one?
Or, is it legacy from before you owned it?
In either case...
To verify that I am correct in your horn operation, we are going to test the bit inside the horn boss you can see that creates the contact.
If your meter has the audible "Beep" setting on the diode test setting, brilliant, use that. If not, then use the ohms (horseshoe) setting on the lowest range your meter has.
Touch the probes of your meter together to verify that it works correctly (beep or a reading of "Zero" depending on your setting).
Knock your ignition off, and if you can disconnect the ground terminal from your battery.
Find something that is clean metal and definitely either chassis, or directly connected to your chassis, and stick one probe on there (doesn't matter which).
Place the other probe on the wire that goes to the button on your steering wheel, that would make a connection to the steering column when the horn is pushed.
If you get a reading of "OL" or infinite or something (open circuit) you know you have found the side that goes to the relay.
If you get a reading of "Zero" then you know you have found the side that goes directly to earth.
Next step is to verify the readings...
Now touch the probe you touched the wire / connector with against the metal ring of the boss, you should get a reading opposite of that to the last test. If both readings are the same, then we either have a problem somewhere, because there's no path to earth, or your horn is switched live, not switched ground, on the relay side.
If you get the same reading for both tests:
This is where we trace cables. Look at the colour cable that goes to the button, and look for the same colour under your dash. Test between the connector on the button, and wherever that wire terminates under your dash. If you found the right one, you will get your beep / zero reading. One should go to the relay, and one to a live feed from somewhere if it's a switched live, so these are good places to start (the relay and your fuse box).
Now repeat for the wire on the other side of the circuit.
If you get opposite readings for both tests:
You have found the earth path for your relay. But you need to know where these are going, so you still do the test for the above on the cable that gave you the "OL" (open circuit) reading only (you already know that the other end goes to earth). This should be directly on one ofhte terminals of the relay, this is a good place to start.
It's not easy, in fact it is a complete faff chasing cables. But that is all that is required in this instance.
Once you find the relay and verify that the cables that go to and from it are in good order, you can test the relay.
Set your meter to read resistance (Ohms).
Put your meter probes on either side of the load end of the relay (that is, not the two terminals occupied by your horn button). Turn on your ignition. You should see open circuit. Press your horn, you should see short circuit.
If your relay works, simply disconnect the wires going to your switch and connect them to either side of the relay load side (matters not which way round).