Thanks all for the excellent replies. Looks like concensus is a
voltage drop. Can definately see this as the contacts ARE
dirty/corroded. I'll have to see what a little cleaning up will do for it!
Regards
Scottmi 74 MGB (chrome)
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From: Andrew Mace <amace@unix2.nysed.gov>
On Mon, 15 May 1995, Scott Miller wrote:
> Need help sorting out the wiring for my dual lead, dual tone system..
>
> - only one horn or the other will sound - must disconnect one to have
> the other work. tried switching terminals the leads were connected
> to on the horns but no change (I need to experiment a little more
Scott, I'd check the voltage when both horns are connected. Somehow,
despite the fact that you noted original wiring was in place, it sounds
to me almost as if the horns were wired in series instead of parallel!?
Anyway, it does sound like you're getting a voltage drop with both horns
wired up. Maybe there's a grounding problem with one or both horns or
with the horn button contacts?
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From: <KEN@HCACAD.HOLYCROSS.EDU>
I can't be sure but I think that a connector in the loop is corroded
to the extent that it will pass adequate current for one horn to sound but
when two are hooked up the voltage drop across the bad connector is enough
to prevent the horns from working properly. A quick & dirty solution is to
use a relay with its coil hooked to the horn circuit and the output switching
a direct connection to the horns. I did something like that with the air
horns in my 77 MGB and it works great.
Ken Scott
77 MGB
KSCOTT@HOLYCROSS.EDU
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From: "Ramm, Andy" <ARAMM@sv.tbgi.com>
I don't know how the MG horns are set up as I just got my first one a
week and a half ago and don't even know where the horn is.
However, many horns are actuated by a relay, which is rated in amps just
like a fuse. Exceed the number of amps it is rated for, and the relay
switches the circuit off. The relay could in this instance be weak, or
could have been replaced with an aftermarket one that wasn't rated high
enough. In any case, relays are cheap, so if this is the problem, no
need to worry, just switch it for one of a higher rating, or better yet,
run two relays -- one for each horn.
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From: "W. Ray Gibbons" <gibbons@northpole.med.uvm.edu>
I think you have a high resistance in the circuit, so the voltage is too
low to operate both horns. The ground is the first place to
check--connect a wire between the horn body and ground, see if both now
will work.
Ray Gibbons Dept. of Molecular Physiology & Biophysics
Univ. of Vermont College of Medicine, Burlington, VT
gibbons@northpole.med.uvm.edu (802) 656-8910
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From: Will Zehring <wzehring@cmb.biosci.wayne.edu>
>2/ is there _enough_ current getting there? (either horn is strong)
I am *not* an expert on these things but I would suspect that in fact the
above is close to the problem. I was hunting for some horns last fall and I
went to my local used MG parts place. Yes, he had horns, but he didn't want
to sell any to me. Why? he said they were old and the drew too much
currant to make any sound anymore. He suggested just getting new ones,
which I did (tho I have yet to install them as the same spring swtich on my
car is defective and I'm just sort of balking at taking care of it). I
wonder if that isn't the problem with yours: one horn alone is ok but the
two together is just too much.
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From: Jay Tilton <jtilton@vt.edu>
This one has stumped me before. I seriously doubt there's anything wrong
with the horns, wiring, or switch.
If you've got a voltmeter on the car, watch it as you stab the horn button.
Drops pretty low, doesn't it? The horns draw an amazingly high current.
Try it with the engine running. I'll bet the extra volts from the
alternator will make the horns work.
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From: MR JOHN E LIFSEY <GJCW23A@prodigy.com>
Scott, I'm having trouble following your trouble shooting
procedure. Best way to start is to bring a hot wire from
the batter to the positive terminal of each horn. If both
work separately, then connect a jumper wire between both,
and connect a hot wire to it. If they work then, you have a
wiring problem. If they don't both work then, you probably
have a grounding problem. To test that, connect a wire from
the ground side of one horn to the negative side of the
battery. If one sounds and one "phtts", you have a ground
problem. Anyway, you get the idea, isolate the problem then
you can track it down. Good Luck, finding electric problems
can consume a lot of time. My experience has been that most
are simple problems of bad connections due to age and
corosion. I always enlarge the wiring diagram of the
circuit I am working on and highlight it with a yellow
marker to help me once I know it is in the wires and not the
load.
----------
From: <GELEWIS@aol.com>
It sounds like you have a voltage drop problem, that is not enough current
getting to the horns to run them both. If you have an voltmeter, put on lead
on the source (hot wire to button) the other on the horn terminal. If when
you press the button you get more than .25V you have too much resistance in
the wiring and or button.
Mark
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