Horn relay

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Guido

Guido

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I am installing a new car horn which came with a relay. These will be dual horns, hi-lo.
My question is can the relay be wired with the power coming from the negative side, is there a problem wiring it with a pos ground system?
I tried the search but no luck as I am probably doing the search wrong.

The relay is a 4 post type
 
For what it's worth, I have just a single VW horn on my MK3 simply wired as originally, using existing horn wiring. Have had no issues. I know this is not what you asked, but it's related and thought you might find it useful.
 
As long as the body of the relay is not earthed than it can be wired +ve or -ve, just needs working out.
 
Thanx. It is a solid plastic body so no, it won't ground out.
Once I get these installed and working it's gonna be fun hitting the button as these horns are loud. 110db
 
It depends...some automotive relays have a flyback/snubber diode wired across the coil and in that case the polarity DOES matter, if you get it backwards the diode will be a dead short and blow a fuse. I'd look up the relay specs to see. Do the terminals on the relay have standard numbering?? (like 30, 85, 86, 87, etc.) The case of the relay might have a diode symbol on it too...

Horn relay


Horn relay
 
The horns came from Harbor Freight. They are the snail type. The 4 pole relay came with the horns but since these horns and relay are not self grounding I will wire them as if they are being installed on a neg ground system.
That should be fine, right?
 
Let me get this straight.
I should wire TERM 30 to the hot on the bike, which is NEG.
The 2 TERMS, 85 and 86 take the wires that come off from the old horn and get connected there.
And TERM 87 is the power out to the new horns, right?

I know all this has been discussed before but for the life of me I can't figure out the search function on here.
 
Guido said:
Let me get this straight.
I should wire TERM 30 to the hot on the bike, which is NEG.
Click to expand...

Yes. Connect '30' to battery negative (preferably with a fuse).


Guido said:
The 2 TERMS, 85 and 86 take the wires that come off from the old horn and get connected there.
Click to expand...

Yes. Connect the horn button wire (normally purple/black, '71-on) to one terminal, and the other terminal to 'red' (+) or to a good earth/ground (as there's no internal relay diode it shouldn't matter which way around you connect the two wires.


Guido said:
And TERM 87 is the power out to the new horns, right?
Click to expand...

Yes. (it's odd that the layout diagram on your relay shows two 87 terminals but it appears to have only the one?)

Horn relay
 
They have used the same relay case for a 4 and 5 prong relay. There can be an 87 and an 87A. It's not the highest quality relay out there. Probably closer to the lowest you can get. But it will work. Maybe. :mrgreen:

Doesn't matter. From relay to horn use 87.
 
Great! Thanx for all the help.
Being color blind has not let me really learn wiring without the help of others to point out the colors.
This has been a big help.
These horns come chrome out of the box. I painted them black and will find a suitable place to mount them.
I will try to hide them. Freaking loud they are.
 
swooshdave said:
There can be an 87 and an 87A.
Click to expand...


There can, but then one would expect to find the layout diagram and one terminal marked 87A, as 87/87A would be a 'change-over' relay rather than a 'twin make and break':
Change over relay:
Horn relay
 
I do have a 2 spade fuse holder to put in. What size fuse should I use?
I'll post a pic of my location for the horns when done.
 
Guido said:
What size fuse should I use?
Click to expand...

That can depend on the actual type of dual "car" horns.

Assuming you've used heavier (than standard) gauge wire (for 30 & 87)?
Probably around 15-20A.
 
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