Electrical (horns) question

[Alec Dawe]

Having a good clear out of the shed the other day, prior to demolition and rebuilding of a MUCH larger shed (partitioned off to take Volvo bits as well!) I found lurking a set of '70's Alexander Air Horns, bright red trumpets et all

Having freed up the compressor, Lo and Behold, they work, so, going back to me Boy Racer roots (Mk 1 Cortina, lowered, wide wheels, HUGE exhaust etc etc.) methinks, I'll fit them to the 240GLT Dredged memory for the wiring connections to the relay, sorted that out with battery and multimeter, etc. Fitted to car, take 'signal' for relay from existing horn feed, take precautions of NOT connecting pipe to horns, and turn ignition on for test. Compressor runs as soon as ignition on????

Scratch head?? Only explanation can be that the existing feed to the Volvo twin horns is permanently live when the ignition is ON, and that the Volvo switching is on the earth return side??? Can this be right? Does anyone out there know?
Its not a huge problem, just means swapping the relay control wiring about a bit, but does seem odd to me.

[RichardB]

Ive fitted air horns to my 740 and mine is negative switched, I think this is the way Volvo do it. Also I didnt use the standard size cable because it is way to thin and resulted in the horns not sounding very loud, I replaced it with some 8 gauge straight to the battery, much better.

You can check if it is negative or positive switched with a multimeter using the existing horn wires but im sure it will be negative the same as the 700's.


Cheers,

Richard

[Mike_Brace]

Yep! You sussed it - live feed to horns and switches to earth via steering wheel.

Mike

[Alec Dawe]

Thanks Mike, I was sure that you would know the answer... what a bizzarre idea.. never mind, at least I know now that it is what it is, and that someone has not bu88ered about with the wiring in the past

And, yes Richard, the wiring supplied with the horns originally was WAY too small, voltage drop was awful, plus it got HOT!

I got rid of the makers stuff, (apart from the relay switching feeds as they only carry very small current,) years ago, and the compressor has 20amp rated copper, and a decent earth connection too.

[Peter D]

So what you should have done, and might have done, is provided a fused feed 20Amp or so to the contact of a decent relay and the coil + contact, then connected the other end of the coil - to the switched earth feed and the other contact to the Horn compressor and grounded the other side of the compressor. Watch out for radio intererence from the hown but it should only be used in an emergency, hooting at friends and other Volvo's is a breach of the road traffic act and gets right up my nose. Regards Peter

[Alec Dawe]

Originally Posted by Peter D

So what you should have done, and might have done, is provided a fused feed 20Amp or so to the contact of a decent relay and the coil + contact, then connected the other end of the coil - to the switched earth feed and the other contact to the Horn compressor and grounded the other side of the compressor. Watch out for radio intererence from the hown but it should only be used in an emergency, hooting at friends and other Volvo's is a breach of the road traffic act and gets right up my nose. Regards Peter

Aha`!
Can't do that. I was going to but thought about it, and of course, the 'earth' side of the horn wiring is at 12volts until the horn push is made, and connects this side to earth properly, so effectively, all the wiring for the volvo horns is live at 12v right up to the horn push/relay contact.

Connected feed for relay coil to 'live' side of original horns supply, and 'earth' side of relay coil to the 'earth' return side of the original horns wiring. Decent, fused, 20 amp connection to relay contacts to air horn compressor and a decent earth, and presto, everything works.
I know that this means that the relay coil etc will be at 12v potential as long as the ignition is on, but no current is passing, so no problem. If the volvo horns can operate like that, I'm sure a relay coil will be quite happy.

Question for Mike Brace if he happens to read this.. on the left front wing, just behind the power steering resevoir, and next to the dipping relays etc is a little black box with a sliding (upwards to open) cover. Inside this is what looks like a distribution busbar, with spare spade terminals (male) on it. Is this what it seems to be, a power (12v) distribution box, and if so, is it OK to connect the feed for a pair of driving lights to one of the spare connectors do you think?

[Mike_Brace]

I see you're gradually working you way round the car and finding all the delights of Volvo thinking. Yes, this is the point to use.

Mike

[Peter D]

Alec you must have mis-read or mis-understood my text as the way I describe the connection is correct and exactly how the normal horn wiring works. You are just placing a relay coil effectively across the horn coil. Yes the sliding cover reveals a 12v buss bay for extras. What do you mean driving lights. i.e 5/12 watt side light bulbs. You already have them in your from side lights or you have dim and dip head lights depending on the age of the Volvo. Regards Peter

[Alec Dawe]

Originally Posted by Peter D

Alec you must have mis-read or mis-understood my text as the way I describe the connection is correct and exactly how the normal horn wiring works. You are just placing a relay coil effectively across the horn coil. Yes the sliding cover reveals a 12v buss bay for extras. What do you mean driving lights. i.e 5/12 watt side light bulbs. You already have them in your from side lights or you have dim and dip head lights depending on the age of the Volvo. Regards Peter

Sorry Peter, I misconstrued your message.

Driving light I meant as in long range driving lights, to suppliment the rather poor main beam on from the standard 240 headlights. I have wired these up now, relay controlled from the main beam wiring, so when the 'extra' driving lights are 'on' they come on with main beam, and go out again on dip.

I was worried that taking the relay signal from one side of the headlaighs main beam might make the bulb failure warning operate, but thus far it seems to be ok.

[Mike_Brace]

Originally Posted by Alec Dawe

Driving light I meant as in long range driving lights, to supplement the rather poor main beam on from the standard 240 headlight

My Italian 240 had brand new headlights fitted for its MOT (knackered reflectors and lhd lenses). On main beam the lights are pretty good. I must agree the supplementary driving lights are bonus though.

Mike