Changing of NC horns

Technical Area Electrics & ICE
1

  1. My model of MX-5 is: _NC_SE (2007)

  2. I’m based near: Nottingham

  3. I’m looking for technical help: _Horn wiring technical knowledge.
    I have bought a pair of Ring single electromagnetic horns (Low & High note) I have taken the plastic guard off and mounted the horns. My questions are;

  4. Are the original horns a Positive Acted Type or Negative Acted Type?

  5. The wiring diagram suggests a relay for each of the new horns (no relays in the box) so a separate purchase. Are the new relays required there were 2 horns fitted as standard?

Cheers
Keith

2

You need to check the amps drawn by old and new horns.
If the new horns draw the same or less, you should be fine with the existing wiring.
If they draw more, you may need to uprate your wiring and relay(s).

1 Like
3

some horns mean that the 15A fuse can’t cope and blows.
Some say a 20A fuse is OK
Others say NO

4

If you have access to a multimeter, measure the resistance in ohms across the horn terminals.
Lets assume you measure 3 ohms.

Assume the cars approximate voltage at 12.5v.
Divide 12.5 by the ohms measurement (in this case 3)
The result is the number of amps drawn.
In this case approximately 4 amps

This will allow you to make an informed decision as to whether or not you utilise a relay.
I didn’t bother, on the basis that the horn gets used once per year for the MOT.

1 Like
5

i put relays on when i did mine

6

As I understand it, the horns are protected by a relay as oem but a fairly low-rated one

7

Thank you to all who replied to my post. I have successfully installed the horns today without the extra relays. I established it was a Positive Acted Type circuit as manufactured. The instructions for the horn said protect with a 10amp in line fuse. The Mazda circuit is protected by a 15 amp fuse so my assumption was my choice of horns did not pull a lot of amps when in use. The result is a much louder horn than the original system ideal as was stated people do not hear horns for stereos etc. Fingers crossed that is my problem solved.
Cheers
Keith

3 Likes
8

That sounds great, Keith. I don’t know if videos or sound clips can be posted on this forum but if you could it would help to tell how loud the horn is now. Thanks in advance

9

Hi, Sorry I cannot send you any sound recording, I am on holiday until the end of the month. I fitted a pair of horns (high and low range) if that helps. They are certainly loud enough to be heard when required.
Cheers Keith

10

Hi i need to change my pathetic bleep too. which one did you use ?

11

I replaced mine with these. You just have to run a wire from second terminal on horn to the mounting bolt to earth.
HELLA Signal Horn - S90 - 12V - 113dB(A) - Set - 3AM922000-971 | eBay

12

Hi, I went to my local motor factors and purchased a Hella high and low horn. Nothing special but totally effective. Hope that helps.
Cheers
Keith

13

The advantage of the Piaa horns is that they are higher pitched than most and imho, that matches the car, so anybody getting hooted at will find it easier to quickly identify which idiot is hooting at them.

1 Like
14

I had a pair (2 compressors) on mine. They blew seperate 2 horns mounted behind the nose (NC1) 2 sets of these