how can I trace horn wiring?

[cubby911T]

Preface: I am not very experienced with wiring!

Since I've given up on removing my steering wheel (for now), I'm wondering if I can trace my horn wiring effectively without removing the wheel.

You see, one of the PO's of my 70T decided to splice in a P.O.S. security system and part of that system included tapping into the horn wiring under the dash. Well, I've stripped the security crap out, and now my horn is dead because I can't figure out which wires to splice back together. I know where the wires are that lead to the horn, but I can't find the ones that lead back to the button in the steering wheel.

Does anyone have any suggestions on how to identify the horn wiring as it emerges from the steering wheel? (ie: wire color, routing, anything?)

thanks,

[autobonrun]

I don't have a wiring schematic for a 70 but see if what I found for a 1974 in a Clymer shop manual looks like what you are seeing.

Quick and dirty, first swap the horn relay for another relay you know works and see if this fixes the problem. The relay is probably not bad but I'd hate to see you spend hours doing other checks when you can do this one in one minute and remove this possibility from consideration.

According to this manual, the hot wire from the fuse to the horn relay is red. The wire from the relay switch to the horn itself is black.

The wire on the horn relay coil is also red. The ground side of the coil is black/white and goes to the horn switch. From the other side of the horn switch the wire is black. So if you look at your horn switch, you should have one black/white wire and another wire all black to ground.

To trouble shoot, see if you see 12vdc to the horn relay from your fuse. This will be at pin 86. If you don't have 12v there, this is your problem. The horn switch actually switches the ground wire, not the hot wire so you will never see 12v at the horn itself.

You may possibly have lost the ground path. To check, find the black/white wire at the relay coil and lift it. Place a voltmeter from this wire to a known ground point. While holding this in place, have someone press the horn. You should see the resistance go to zero. If not, this is the part of the circuit that needs to be traced out to see where the ground is lost. It would either be in the black/white wire from the relay to the switch, or the black wire from the horn switch to ground. Just a guess, check the black wire from the switch to ground first.

All this assumes the wiring in your car is the same as that in the 1974.

Check the Pelican wiring diagrams on this site to see if they have the circuit for your car. If you don't know where it is, I can look and post a link.

[cubby911T]

autobonrun,

Thank you for the detailed reply.....you've given me what sounds like a good start.

[911pcars]

I've got some electrical diagrams here. One of them might help.

Sherwood
http://members.rennlist.org/911pcars

[Early_S_Man]

Matt,

Pelican has a '71 diagram [shown below] that should suffice ... Porsche made very, very few changes to the wiring color code over the years ...

It looks like you should be looking for a Brown/White wire coming out of the steering column!

[cubby911T]

Warren,

Thank you! and a question regarding the suspected brown wiring.....do you suppose that brown wiring would be contained within some factory conduit? There seem to be 2 black conduits emerging from the steering column under the dash.....I guess I'll just need to peek inside each one.

I'm pretty illeterate with wiring diagrams, but I should make an effort to study and learn how to follow them.

Thanks so much for your help,