Is it OK to wire multiple switches to 1 relay?

Yay first post! Let's get to it.

I have a bosch 5pin 30 amp 12v relay.
I plan to operate 4 exterior 13w led spot lights on my rv from a stand alone fuse box. I would like to have an on switch in the cab, and an on switch by the bed in back. I would also like to attach the headlight trigger from my avital alarm to the same relay (which I think is 200ma).

The question is, can I simply attach all 3 "on" sources to the the 1 relay and leave it at that? The 2 normal on off switches would get 0.5 amp fuses to limit current. I feel like I would potentially have an issue with alarm trigger, do I need diodes? If I do need diodes, I'm not sure what size or which direction they would go.

Thanks ahead of time for any clarity. I've seen a million wiring diagrams for relays but I have seen 0 that use 2 separate switches for 1 relay plus a car alarm trigger.

You don't need fuses in series with the "on" switches.
Connect one side of relay coil to 12V.
All the switches will be connected on the ground side.
Any generic diode rated at 1A/100V or greater will work (1N4002,1N4003/4/5/6/7 - I use 1N4007 because I have a large supply).
Use 1 diode in each feed to the coil - the 3 anodes connected to the 'other' coil terminal.

You should put a suppression diode across the relay coil terminals to prevent damage to the alarm - cathode attached to the 12V coil terminal.
You need a proper Schottky rectifier for that - the generic diodes are not adequate. Use 1N5822 for the coil suppression.

Thanks for those specifics eguru. If I can bother you with one more question ?

Considering my lack of knowledge with cathodes and rectifiers, would I be better off using 3 relays?
Or 1 relay for the passive switches, and 1 relay for the alarm trigger?

The simplest, cheapest and most reliable method is to use just one relay and the rectifiers. In fact you really don't need a rectifier in series with each switch and the alarm output.
It would be sufficient to only have only the one rectifier in the feed from the alarm.

No suppression diode needed. The alarm is already planning to have a relay connected to it. There is a diode in the alarm.

I really do not know why there is even any mention of a diode other than in his initial question.

Power 86. Connect the switches and the alarm to 85.

i am an idiot wrote:

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No suppression diode needed. The alarm is already planning to have a relay connected to it. There is a diode in the alarm.

I really do not know why there is even any mention of a diode other than in his initial question.

Power 86. Connect the switches and the alarm to 85.

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You need the diode in the alarm output so that when one of the switches is activated it doesn't also pull down the alarm output and turn on the siren/etc that are also connected to the alarm output.


The local suppression diode may not be needed but it will be more effective right at the coil than the one in the alarm.

My questions are answered, thanks very much. I usually just put things together and turn em on to see if they work. But I mounted the alarm brain in a safe under the water tank with metal conduit. Replacing a burnt brain (or hacking it out by a thief) is quite difficult.
In my application my alarm brain is connected to the chassis battery, but the spot lights will be ran to the house battery bank. The two battery systems are rarely the same voltage and I've had issues with the alarm going off when my solar kicks on in the morning due the voltage difference at grounds. I knew I would have to use some kind of diode on the alarm trigger simply because the two on switches will generally be 2 volts higher.

Thank you again.

There is not going to be a 2 volt difference. Alarm has a ground output. You do not need a diode. When you connect a horn honk output wire to the horn, do you have to use a diode? What happens when you blow the horn and it puts ground on that wire without a diode on it? Same difference, ground from the horn switch vs. ground from one of your switches.

I doubt that the OP wants the horn to sound when he uses a switch to turn on the lights. So the diode is necessary.

Towel.