General Tech Yes, the Horns Again--Electrical TR4A

[KVH]

To start, I have good ground up the column to the horn button. I also have power to the horn relay. I cleaned up the relay points. But still no horn. I hope I haven't shorted out the relay--my new one from Moss has never worked. I keep it in a box, as if I can return it after 7 years. No matter what connection permutations I try, that new relay is a waste, so I'm using my trusty 56 year old British one.

Some questions: a) does the relay casing need to be grounded? I can't tell if something internal might rely on another ground even though the purple and black wire to the horn button is grounded when I push the button; b) it appears the relay is upside down. I see W-1 stamped below the connector, and of course it looks like M-1--sound right?; c) does it make any difference which wire goes to which spade connector on the horns?; and d) can I somehow bypass the relay just to hear the beautiful sound of my horns? At least I'd know the old lady is awake.

Any other advice on this? Thanks in advance.

 

[poolboy]

If you can put 12 volts on one of the actual horns spades and ground the other spade, the horn should sound if it's working.
Where you just need a 12 volt positive source, a few amps and a negative connection I use a battery charger to test things like that.
As far as the relay...if you get 12 volts coming out of the C1 terminal when you depress the horn button on the steering wheel, it's probably wired correctly and the relay is doing it's job.....If not go back "upstream" and see what's going wrong.

 

[KVH]

Got it! Fixed. I researched prior posts and found that for the new relays you have to jumper posts C-2 and W-2. Now we all know, again I guess. Anyway, all good.

 

[KVH]

I really shouldn’t leave this subject without first asking you folks who understand “electrics”—why must we jump C-2 with W-2 when installing the newer horn relays?

 

[Geo Hahn]

I suspect it's because you're asking the relay to provide a ground (whereas most relay applications are done to provide power).

But that's a guess and I've already had my second glass of wine so consider the source.

 

[Sarastro]

I really shouldn’t leave this subject without first asking you folks who understand “electrics”—why must we jump C-2 with W-2 when installing the newer horn relays?

I think it's because W2 and W1 are the coil, and C1 and C2 are the switch contacts. In the original relays, the W2-C2 connection must have been made internally, so there was no external W2 contact. In the newer ones, it appears that the internal connection doesn't exist, so you have to make it externally.

Frankly, I'm done with using those old relays in cans. The final straw was when the internals of one shorted to the can body and blew my horn fuse. You can use ordinary, modern, Bosch-type automotive relays in place of them, and they are more reliable and cheaper. In those relays, terminals 85 and 86 are the coil, corresponding to W1 and W2, and 30 and 87 are the normally open switch, corresponding to C1 and C2.

 

[Popeye]

Basically, you jumper W2 (85) and C2 (87) to provide power to both.

Pushing the horn connects W1 to ground - completing the W1-W2 circuit, which in turn closes the C2-C1 switch. C1 connects to the horn, in turn which goes to ground.

In a normal relay install, the W2 power input comes from “far away”, eg a light switch, and the intent of the relay is to reduce current on long runs of wire / frail switches. However, I’m this case the input power is “local” and the ground is “far”. Thus both sides of the relay can get power from the same source - the jumper.

(I’ve been studying relays and OD wiring, figuring out how to add a diode…. Not saying I’m right, but I have a few schematic sketches in front of me and just placed an order with British Wiring and Digital-Key.)

 

[Popeye]

I've already had my second glass of wine so consider the source.

May we join you?

 

[Rod-H]

c) does it make any difference which wire goes to which spade connector on the horns?;

If you connect them backwards, they will literally suck sound right out of the air.