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PDM + Alarm horn wiring

EFI Wiring Fundamentals

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Discussion and questions related to the course Motorsport Wiring Fundamentals

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I am re-wiring my entire car and will be installing a PDM as well as a keyless entry/start system. I'm planning on connecting one terminal of the horn to a 15A output on the pdm, with the other terminal to ground.

The alarm system must also be able to activate the horn, whether the PDM is turned on or off. The issue is the alarm documentation says the system activates the horn from the ground (negative) side.

I have attached to this post a solution for the wiring and I'd like to confirm if this is correct or if it will cause an issue with the PDM when the alarm activates the horn? Or do I need to use 2 relays?

Attached Files

Hi Eric, what you've proposed is exactly how I'd deal with this. It's not the most elegant solution but it will get the job done.

Thanks for the confirmation Andre. Yes, it's too bad I have to use a relay, but the PDM saves me from needing another 14 relays and 24 fuses. I can live with one relay. :)