Horn issues - pressing horn = horn + wipers!

[Mark-ixql7]

Hi all,

The other day I got cut up somewhere, went for the horn and nothing happened. Kind of forgot about it, but got a reminder yesterday that my MOT is due at the end of Jan, so I should probably look at getting it sorted!

Here's the symptoms:

Ignition off = intermittent (maybe) weak / odd sounding horn. Seemed like I had to wiggle the steering wheel around. I took off the steering wheel boss and cleaned the ring. Still a weak / odd sounding horn, but I think it's solved the intermittent issue at least.

Ignition on = weird sounding horn, but it also makes the wipers do a single wipe (as if you pulled on the stalk to do a wash / wipe)

Searching around has come up with a few things. One post suggested it could possibly the o/s earth point in the transmission tunnel area. I sliced the carpet and that bolt seems tight.

I did find someone suggest that there's some kind of ground under the steering cowl / steering column area, but I'm failing to see anything there?

Another post had issues with the horn making the indicators / high beams / wipers go following a chassis refurb suggested the front frame earth could be the issue - the annoying one under the rad hose. I can just about sort of see the bolt and it doesn't look horrendous at least, but I can't get a spanner on the damn thing.

Is is likely to be this front frame earth? Anything else I could check before having to undo that hose to shift it out of the way and get coolant everywhere?

Cheers

[Mercdriver]

Why not use a jump start lead from the battery earth to a good earth point on the chassis and see if the fault disappears?

If it does then your earth lead is problem.

I bought a 1973 TVR 2500M and ended up running earth wires to a terminal block made out of copper bar then running each earthed item to the block, only way I found on the car to provide a good earth.

Edited by Mercdriver on Friday 29th December 12:52

[Mark-ixql7]

So just run a lead from battery earth to somewhere near by that front earth point do you mean?

[Belle427]

Here is the horn circuit, ground is front chassis offside.

[Mercdriver]

Not necessarily, any good earth point maybe on engine itself, you are trying to bypass the possible poor earth at the front. If your new wire solves the problem then probably the front earth point is poor and you will have to strip clean and re assemble,

I used serrated washers on all the earth points as they bite into the metal of the chassis and the wire terminal

[Mark-ixql7]

Ok, thanks both!

I just tried running a chunky jump lead from battery to close to the front chassis earth at various points - catch can mounted to upper chassis near rad being the cleanest one - and that made no difference.

Annoyingly it's just started raining. I can try some other points whenever the weather decides to stop!

Oh, also, not sure if it's worth mentioning but I don't seem to have a relay in position 4 either. There's yellow ones in position 1, 2 and 3, then blank 5 and black one in position 5. Horn was working fine and passed MOT last year and I've not touched anything...

Edited by Mark-ixql7 on Friday 29th December 13:46

[Mercdriver]

Try clipping it to the door lock or a door hinge, partially unscrew one bolt to save damaging the paint to get to clean metal.

You need to get a good earth away from the front end of the car to eliminate the front earth point.

If fault disappears then fault is front earth point, if fault persists chances are front earth is ok and I would investigate further at the steering column.

Don’t you just love TVR electrics?

[Belle427]

Test the horn on a good 12 volt source as it may be knackered and your chasing your tail.

[Mercdriver]

A very good point! Use a wire from earth on battery direct to earth on horn, if it sounds then earth faulty.

If not then take a feed wire from live of battery to live side of horn if it works then feed wire to horn faulty.

Horns are usually wired live all the time and when you press the horn button you earth the horn and it sounds.

[Mark-ixql7]

Ok, so I tried clipping the jump lead to various places including the door latch, and it made no difference.

It does kind of sound like maybe one of the horns is on its way out or something. I'll try and get a video if that would be useful.

Assume these are the horns (hopefully pics upload)? I've read they're a bit of a nightmare to replace, especially on the later cars with the bar instead of grille, but it doesn't look too bad to me... Famous last words! I may just replace them blindly to be honest as one of them looks a bit scabby! As does the radiator, so I may replace that as well which would presumably give good access to the horns and earth bolt, if it really is a nightmare to replace from the front!

Thank you for your help! I hate car electrics

[Adrian@]

The pictures run ..alarm siren then horn (one of two, which there is a high and low) and radiator core (failing). A@

[s p a c e m a n]

I doubt that there's much point in using the door latches to earth on a fiberglass car..

Pull the horn relay out and jump the pins to activate the horn, if the horn works and the wipers don't move then the fault is probably on the horn button side of the circuit.

[Mercdriver]

[quote=s p a c e m a n]I doubt that there's much point in using the door latches to earth on a fiberglass car..




Oops, silly me, bottom of the class, sorry. Should have said the door hinges they are usually bolted onto a bit of the chassis.

[Belle427]

If the wipers operate too it has to be a ground problem really, either the trans tunnel one or the front chassis.
Worth taking the bolt out of them both and checking the condition of the cable eyelets etc for cleanliness.

Edited by Belle427 on Saturday 30th December 16:25

[Mark-ixql7]

Ah, assume the other horn which I mistook the alarm siren for will be in roughly the same place somewhere? Maybe that's why people say it's a pain, as I couldn't see anything else with my brief look around!

I did wonder whether the door latch bit would be grounded in any way 🙃 but I tried quite a few other points and it made no difference anyway.

Don't suppose anyone would be able to help with which is the horn relay on my car? I don't seem to have relay 4 (as described in a previous post), which seems to commonly referred to as the horn relay. I guess I can probably just pull relays until the horn no longer half-works and assume that's the one?

[Belle427]

Some other fusebox layouts here.
https://www.pistonheads.com/gassing/topic.asp?h=0&...

[Belle427]

And an official manual one

[Mark-ixql7]

Thanks!

Mine doesn't seem to match any there, but some searching suggested it should be in the owners handbook... Which I have! Lo and behold, that seems to match.

I'll give this a go whenever the weather decides to behave for a bit and see what happens. Ta!

Posting a picture here just incase it might help anyone else with what is quoted as the m1238 fusebox. I'm not sure if that's a standard number or specific to this layout etc

[gavgavgav]

As you can see and get to the wires behind the horn sounder, to rule out the horn connection to the front chassis earthing point (which is a pain to get to) unplug the existing earth and make up a single earth lead and connect it to the engine.

[pmc_3]

When I was trying to find a horn issue on mine (only worked when turning the steering) it was a slightly loose nut on one of the column mounting bolts, there was a ground wire on that.