Spitfire 1978 Spitfire Horn trouble shooting

Im trying to trouble shoot the horn circuit on my Spit. I bought a
new indicator/horn switch and installed. the button was broken on the
old, so i thought that might do it. But when i press the button, I
dont see voltage at the horn.

I jumped each horn directly to the battery , drivers side does not
work, passenger side does.

The headlight dimmer high beam works, which I think is also on the
purple bus.

Im thinking the easiest thing is to just run a new wire from batter
to the switch with an inline fuse, and another from the switch to the
horns, with trying to find out exactly where the problem is.

The hazard flasher also does not work Im thinking this may be related to no voltage on the purple wire?


Any tips on abandoning wires in place and running new?

Joe, I don't have a Spit wiring diagram handy, but isn't the horn switch in the ground side of the circuit? Purple hot at all times, and pushing the button completes the ground leg?
My memory is fading fast, but I seem to recall that if there are two wires to each horn, then that's the way it's done. A single wire hookup would ground through the horn body.
Jeff

https://www.triumphspitfire.com/wiring.html

here's a link to the wireing. Yes its hot all the time.

I was going to use the old switch connector as a break out tool, and see if there's voltage on purple going into the switch

Ah, well. I said my memory was gone! /ubbthreads/images/graemlins/blush.gif /ubbthreads/images/graemlins/grin.gif
Jeff

Joe - I think you are on the right track with your previous post. You should have voltage at the 'hot' (fused) side of the horn button on the purple wire circuit. The high beams should also come off that bottom fuse, so if they are working it shouldn't be the fuse itself.

Does your cigar lighter work? Ignition key lamp? Passenger lamp? All those are also coming off that fuse.

If those are working, and the hazard switch (which is 'south' of the horn button) is not, then it must be either a broken wire somewhere between the fuse and horn button, or one of the connectors in that chain is corroded.

I have had a lot of problems with the fuse mounting clips themselves. Usually though it will affect the whole circuit. Might be worth checking. There must be a junction somewhere in that circuit downline of the fuse - that would be my first suspect area.

Why not try a jumper wire from the fuse clip on the firewall around to the horn button? Disconnect the current horn button wire and run the jumper from the fuse mount to the horn button instead. If that works, and if all the other purple circuit stuff works except for the hazard switch you must have either a bad wire or junction. I would hate to leave a bad wire in there permanently, just in case some day it decides to short.

thanks guzal, staring at the wiring diagram i realize that none of the purple "bus" is working. I the high beams work but the dip does not. neither does the light, flaser, etc. I just got the car. Ill check the fuse, maybe a bad contact or fuse, or something hangin on the purple bus is shorted. I did get continuity when i demated the horn/turn/hi beam switch connector to the horn, so the purple/black wire to the horn is ok.

Aha.

Watch out for the fuse mounts themselves. I have found them to be kind of dodgy and intermittent. The fuse itself may be ok, and if so try cleaning up the fuse mounting clips on that bottom fuse.

If you can get continuity between the fuse mounting clip and the horn button, the wire itself should be ok.

Re: 1978 Spitfire Horn trouble shooting, Solved!

After pouring over the wiring diagram, buzzing out, yes I realized to simply check the fuse, and yes it was blown. Replaced it, now I have 12 volts to the horns!, Hazard flashers that work!, and courtesy lights that shine!.

Hopefully the blown fuse was a fluke, or the next trouble shooting will be a why it blew!

The horns themselves are shot, anyone have luck with generic horns from NAPA?

Re: 1978 Spitfire Horn trouble shooting, Solved!

Could have been the horns themselves. If they are in bad shape they may be drawing too much current and blowing the fuse. Your Spit probably does not have a horn relay as earlier ones did, so a bad horn could conceiveably load up that circuit pretty good.

Did you replace the fuse with a British fuse? American 35A fuses will draw a lot more juice before blowing. If you're using and American fuse I would go with 25A or maximum 30A.

Re: 1978 Spitfire Horn trouble shooting, Solved!

Since a typical Lucas fuse as used in most Spitfires was "35 amp/17 amp CONTINUOUS," I would think that a 20 amp "American" fuse would be about the limit?

Re: 1978 Spitfire Horn trouble shooting, Solved!

Joe, if all you are looking for is audibility, the NAPA horns are fine. If I remember correctly, they have a decent variety to choose from.
Jeff