21 replies to this topic

[minidan]

Model:cooper
Year:1990


this is confusing me a bit...

i have recently wired in my new musical airhorn but it would not work when wired exactly according to the instructions.

now after i got the horn to work, i found that after a day or two my battery is dead lol.

the horn uses a relay and you have bridge two of the terminals to get the horn working. is it possible that somehow i have made a terrible mistake and when left alone my horn can drain my battery??

wiring always confuses me i just cant understand this.

[robtheplod]

probably best to make sure you wire it to a circuit that is only live when the ignition is on, so if you do wire it wrong etc it's only live when you're driving instead of all the time as it sounds at present...

[minidan]

probably best to make sure you wire it to a circuit that is only live when the ignition is on, so if you do wire it wrong etc it's only live when you're driving instead of all the time as it sounds at present...

yea i have wired it to the horn fuse. 2nd fuse down and on the left hand side of the fuse box. but can someone explain how a horn that is not being used can drain a battery?

[il-barba]

i think your relay is being constantly on and you have wired the horn directly in the switch

[jwb_moto]

I think im right in saying that the horn is a perm live as you can use it all the time. If your draining the battery id say there is a bad earth somewhere which is draining the battery.

how have you wired it through the relay? if you tell us what wire connects to which number on the relay we can help more.

[minidan]

i'll check how its wired in to the realy i cant remember off the top of my head.

could a bad earth suck the power out a battery?

[dklawson]

A bad earth will not be the problem. A bad earth connection will appear as an "open" and will interrupt current flow, not make more current flow.

As stated above, the horn circuit is permanently "hot". Also as suggested above, you'll be safer to use a power source that is only live when the ignition key is on... unless your MOT has requirements for the horn to operate with the key out of the ignition.

[minidan]

so whats the best position on the fuse box for an 'ignition only' live.

[dklawson]

I drive a '64 which has 2 fuses. I leave it up to others to advise you on where to tap into a switched, fused circuit on an '90.

[jwb_moto]

A bad earth will not be the problem. A bad earth connection will appear as an "open" and will interrupt current flow, not make more current flow.

As stated above, the horn circuit is permanently "hot". Also as suggested above, you'll be safer to use a power source that is only live when the ignition key is on... unless your MOT has requirements for the horn to operate with the key out of the ignition.

A bad earth can cause your battery to go flat though as ive had this problem on a few cars especially on minis. the last mini that had this problem was caused by the block to bulkhead braided earth being corroded. I replaced this as well as cleaning all the mounting points. This was only became evident when it became difficult/lazy at starting.

Rather that me directing you to a specific outlet on the fuse box its best to check for an ignition live with some testers. Aim to be looking for an outlet that used for any of the aux items. Run this to your sitch and then along to the relay.

when i had musical air horns i ran a fresh supply to the relay straight from the battery as i had the horns in the boot. if you have them up the front you could go direct from the starter solenoid or main battery to starter cable (the big thick cable).

[Phaeton]

As said above it would be best to use a meter & probe around to find a switched live, if you haven't a meter then use a bulb & some wire. For the wiring you should go from the power source found, via your switch to terminal 85 on the relay & from terminal 86 to a good earth, this is your control circuit, when you push/flick/press your switch you should be able to hear the relay click going in & out. Once you have this working then you can move onto the actual air compressor, for this you need a permanent live, the big terminal on the starter motor is a good point to get it from, but remember to disconnect the battery before undoing it, else if you catch earth with your spanner you'll get a nice big splash. Then fit an in-line fuse & connect to terminal 30 on the relay, then finally from terminal 87 go down to your air compressor.

Not sure why your way of wiring it drains the battery, but it could be something to do with the 2 wires on one terminal, I think & it's only a guess you have either earthed your relay through the air compressor or you've inadvertently opened another circuit to earth via the relay.

Alan...

Edited by Phaeton, 07 June 2009 - 04:11 PM.

[stormintrooper]

I think & it's only a guess you have either earthed your relay through the air compressor or you've inadvertently opened another circuit to earth via the relay.

Alan...

would this not cause a major short though? as in the sortwhere wires melt and burn sorta short?

[minidan]

i dont seem to have created short as nothing sparks/burns/gets hot/melts...

but Phaeton , your description of how to wire it up doesnt mention joining two of the terminals together so maybe i'll try that.
i do have a meter so i'll check out the switched lives maybe.

[Phaeton]

I think & it's only a guess you have either earthed your relay through the air compressor or you've inadvertently opened another circuit to earth via the relay.

Alan...

would this not cause a major short though? as in the sortwhere wires melt and burn sorta short?

Not necessarily it could be that he has created a high resistance earth path for something. For instance the air horn compressor is actually a motor which will have quite a high resistance, if he has connected the earth of the compressor through a bulb for instance the bulb would not light & the compressor not run but a current would still flow causing a drain on the battery.

Alan...

[Phaeton]

but Phaeton , your description of how to wire it up doesnt mention joining two of the terminals together so maybe i'll try that.

Might be worth looking on the relay (numbers) & tell us where what wire goes to what.

Alan...