12V Key On Source?

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DRock9

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#1

• May 30, 2008

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I am looking for a 12V key on source in the engine bay, I am in the process of wiring up my Snow Kit and I also have to find a new place to wire my O2 sensor because the 12V key on for those fell far into the harness which I am not about to rip apart to find.

Thanks a lot.

 

D

DRock9

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#2

• May 31, 2008

• #2

Anyone?

 

HISSIN50

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#3

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• #3

If it's just to trigger a relay, you can use VPWR. VPWR supplies key-on power to many of the EEC systems (coil, injectors, A.I.R. solenoids, etc). The charcoal cannister purge solenoid is a pretty handy place to tap into the circuit. See the or/blk wire leaving the EEC relay, changing to red branches.



Thanks to S&2B's (site host) and Tom Moss (author).

 

D

DRock9

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#4

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Are all of those red branches a constant 12v source?

I need constant power to both my O2 sensors and my Snow tuner.

Thank you.

 

Mustang5L5

That is…until I whipped out my Bissell

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May 31, 2008

#5

• May 31, 2008

• #5

Red wire in the Low Coolant sensor located near the battery

 

D

DRock9

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#6

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Thank you very much! That is right about where I need to tap into it.

EDIT: I forgot to add that it needs to be able to support 15amps, is the low coolant temp sensor capable of that?

 

RYC CUKR

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#7

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• #7

If it can't support 15 amps, I don't know the answer, then you can use the power to the low coolant sensor to trigger a 15 amp relay. Run wire from a 12v constant source, fused of course through the contacts on the relay and you will have a 12v keyed source that can support 15 amps.

 

HISSIN50

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#8

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DRock9 said:

Are all of those red branches a constant 12v source?

I need constant power to both my O2 sensors and my Snow tuner.

Thank you.

Click to expand...

Yes, they are constantly hot with the key on and while cranking.

You do not want constant power for your O2 sensors or Snow device because they will be powered with the key off (for no reason). Switched power is what you want, not constant.

As RC said, use whatever source you choose to only power a relay (not the device itself). 30 and 40 amp relays are very common. If you dont need to do anything unusual, a SPST relay should work fine. More common are SPDT relays and they're fine too (you probably don't need to use a N.C. circuit).

Good luck.

 

D

DRock9

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#9

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• #9

Thanks for the help.

I am a huge electrical noob, not much of this makes any sense to me about the relay stuff but I am going to read online to see if I can put some of the puzzle pieces together.

 

HISSIN50

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#10

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Relay is simple.

A SPST relay has 4 terminals, and a SPDT has 5. The only difference is that the latter has a middle terminal called 87A. Simply disregard this terminal when you wire up your relay.

30: fused battery power.
87: Goes to your device (Snow dealie, etc).

85 is grounded.
86 goes to the VPWR or other trigger (low coolant light wiring, etc).

How it works: With 85 grounded and 86 receiving 12 volts, the relay becomes energized. 30 connects to 87 and powers your device with fused battery power.

 

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D

DRock9

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#11

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Awesome! Thank you very much.

 

93 LX

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#12

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• #12

here is a diagram that may help

 

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HISSIN50

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#13

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Note that in the above-diagram, they wired up 87 and 30 backwards from my notation. I follow what I consider the most common convention.


An aside that should not pertain or matter to your application: With little BS 40 amp relays, it doesn't matter if you reverse the common and Normally Open terminals (30 and 87), as was done in the diagram. The same holds true for the coil (85 and 86). But with more complex relays, it can matter.

 

D

DRock9

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#14

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• #14

Ok awesome I can definately set this up now.

Thanks everyone for all the help!