14Sport

Sounds good. Size the feed as big as possible for your later add-ons. Post some pics when you're done.

14Sport

Something I just thought of. That unswitched power at pin 87A would only be available with the key off. So it could be used for an alarm or whatnot. You could add a pigtail to the in pin 30 connection if you want unswitched power that is always available.

dcgrosvold

Right. That would be true for pin 87A of a SPDT relay. However, using a dual-output SPST relay gives you a second switched output. Or you can add a second lead to pin 87 of a standard SPST relay for two switched outputs. And like you say, you can always add a pigtail on pin 30 for unswitched power. I guess it just depends on your application and future expectations for power behind or below the dash.

14Sport

I've never heard that term before. Are you referring to a DPST that has two pin 87s? That would work for two switched outputs.

dcgrosvold

No. I'm referring to a SPST relay that has pin 87 and pin 87A tied together internally. Sometimes the second output nomenclature is different. The same pin is called out as 87A, 87B, or just 87. Whatever the name, its the same pin. The relay is also called a 'dual 87 SPST' or 'dual make spst relay'. You can find plenty of examples on the web.Just Google that last term.

14Sport

Interesting. I did google it. I've never seen one of those with a pin 87b. But it appears to work exactly like a DPST which is strange. But this is what the DPST looks like. I'm not sure if it would easier to find for you or not.

dcgrosvold

No, it does NOT work exactly like a DPST relay. The DPST has two separate switched circuits in a single relay, so you have two separate inputs with corresponding separate outputs. If you tie both inputs of a DPST together, then you would have essentially the same thing as a dual-output SPST relay.

But you could control two separate things with one DPST. Say for example, you could apply 12v to one input and 5V to the other, and then you would have both 12V and 5V switched outputs. See the schematic diagram you provided earlier. This would not be possible with a dual-output SPST.

14Sport

Then that means the one in my picture is actually a dual-output SPST relay since it only has one input, pin 30. I've been calling those DPST relays all along. It has 2 pins 87s. Learn something new every day.

dcgrosvold

Yup. The one in the picture is indeed a dual-output SPST. It's a good exchange, since we both learned something!