switched relay with override

I am looking to add an accessories fuse panel (FP) to run misc items. I want to drive this relay from acc or remote turn on circuit. That is straight forward enough. However, I would like the ability to use a manual (aux)switch to override the relay to allow the FP to be powered when vehicle is off (essentially make it an always on) The normal setup would be the aux switch is off and the FP is hot when the vehicle is running. This way the load is shutdown when vehicle is turned off. In the case I want to power the FP with the car off, say to leave a cell phone charger active, i want to flip the aux switch. Any suggestions would be appreciated.

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TIA Cozman

Diode-OR the relay 86 inputs.
IE - diode between IGN or ACC or AUX or charge light and relay 86, and diode between +12V manual switch and 86, with diode line ends towards 86 (and 85 to GND).
Any 1N400x diode will do, but get (a pack of) 1N4004 else 1N4007 if you need to buy. (They are commonly used for related projects.)

Thank you. Just to make sure I understand I am going to put 2 diodes inline. One each on whatever switched input I use and one between my aux switch. Stripes face the relay and both terminate on 86. Correct?

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TIA Cozman

Yes - provided "2 diodes inline" does not mean inline with each other. (Gotta love English eh? Or unstated qualifications like "inline with each input"... LOL)

Another way of stating it (assuming +12V inputs to relay coil 86 with coil 85 to GND):
Attach one diode for EACH input with their line-end to 86.
Then attach inputs to the free end of the diode.


The diodes are to stop one +12V backfeeding into another input - eg, you don't want your +12V switch to power up your IGN circuit (or blow your alternators charge light D+ or L circuit if used).

I often call this method (diode) ORing from the "logic" OR function - the output is TRUE (+12V or high or active) if ACC or IGN or switch or whatever is TRUE (+12V etc).

Thank you again. I assume there will be no issue if the switch is on and the car is running?

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TIA Cozman

No.

or a SPDT switch. outer terminals of switch to accessory and battery, center terminal to relay coil. switch in one position relay coil is accessory powered, other position by battery.
mark

I should have thought of that...

I prefer diodes (easily expanded) but an SPDT may be easier, tho switching from one to the other may cause a break.