3 Way Valet Switch Diagram - Transister Needed?

incudie · 09-24-2007, 02:57 PM

Hey guys/girls

In the process of setting up a valet switch, which is fine and dandy but I'm confused on one part.

I want to have my computer power up when I unlock the doors with my key fob then remain on once I turn on the car. Along with the traditional valet switch functions.

What I am unsure of is if I need some kind of transistor in the highlighted area or if this would work as is.

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Name: 3way switch.gif
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If someone could kindly tell me if I'm on the right track or not that would be greatly appreciated.

Thanks!

95rodeo · 09-24-2007, 04:15 PM

you could get away with a pair of diodes there, to prevent your domelight from backfeeding into your ignition or vice versa. but your 07 civic should have switched ground not switched 12v at the domelight. if you add a relay on that switched ground you can switch the polarity and it sounds like you would be in buisiness

incudie · 09-24-2007, 05:30 PM

Thanks I didn't know that it was the negative that was switched.

So I think I understand the use of the relay (after three edits lol)

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Name: 3way switch 4.gif
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Would it make a difference if I were to use a coil or photo isolated based relay?

Thanks

95rodeo · 09-25-2007, 12:21 PM

i would use a standard spdt bosch style automotive relay and the funky little black boxes are diodes. sorry i dont have photoshop so this is a mockup from paint

incudie · 09-25-2007, 02:00 PM

no problem as long as it gets the point across ^_^

Thanks a lot!

95rodeo · 09-26-2007, 03:23 PM

no prob

incudie · 09-26-2007, 04:29 PM

Heres an updated version thats a little clearer for anyone thats interested.

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So regarding the -12VDC... where is that coming from exactly if the "switched ground from dome light" would be the negative on the light.

Thanks

95rodeo · 09-26-2007, 05:00 PM

it would be the same as the 12v constant wired at the switch

incudie · 09-26-2007, 06:13 PM

gotcha, thanks!

95rodeo · 09-26-2007, 08:08 PM

once again no prob

afterdigital · 10-11-2007, 08:29 AM

could you tell me why the diodes are facing the way they are (lines on the left)?

Crawdaddy · 10-11-2007, 08:40 AM

Quote: Originally Posted by afterdigital

could you tell me why the diodes are facing the way they are (lines on the left)?

it's indicating current flow as it's depicted on the diode. The current from the 2 sources will be flowing into the switch, but not allowed to flow the other way, so you wont have your dome lights on while your car is on, and you won't burn the wiring for the dome light up while trying to power all the ign switched devices...

afterdigital · 10-11-2007, 08:54 AM