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AZTechBrian, ASE Certified Technician
Category: Honda
Satisfied Customers: 669
Experience:  Owner
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I need to locate 12v only when the engine is running on a

Customer Question

I need to locate 12v only when the engine is running on a 2012 civic? Under the dash or under the hood. Can you help?
Submitted: 2 months ago.
Category: Honda
Expert:  Tracer3 replied 2 months ago.

Hello, I have reviewed your question, I have to pull diagrams and check some things, I will say, right off, engine running 12 volts only? I have never seen that nor can it be done, It can be done key on as well as key on engine running but there is nothing that will supply 12 volts ONLY with engine running, If this is the only option you are asking about? I will need to opt out Please LMK if key on and key on engine running will work

Customer: replied 2 months ago.
that's what I need... a 12 v source when the key is on and the engine is running. In need to power a device when the engine is running only.
Expert:  Tracer3 replied 2 months ago.

ok, bear with me and let me see what i can get from wiring diagrams, back as soon as I can

Expert:  Tracer3 replied 2 months ago.

there are different options, The BLUE wire leaving the igniton switch or as one I picked? the fuse marked B28 in the INSIDE fuse box, You can remove the fuse and parts store sell a tap connector to put in place then snap the fuse in over the connector and then you can tap to this connector for 12 volts as you want. You can also locate the ignition switch, follow wire down the column and tap into the BLUE wire leading from the ignition switch. I have sent information and location pictures

Customer: replied 2 months ago.
B28 is hot when the key is in the acc position, engine not running.
Customer: replied 2 months ago.
The fuse box is easily accessible and I have the breakout to tap in....I d ok nt see 12v only when the engine is running anywhere in the inside fusebox
Expert:  Tracer3 replied 2 months ago.

to recap, I said there is no way to tap in when engine running only. you can only tap to wire etc with key on and key on engine running,. I selected one but yes, may still be powered on accy, i suggested the blue wire running down the column, Here is the igniiton switch chart showing the different ranges in regards ***** ***** position, You cant do what you are asking with engine running only. It can only be done with key on as well as key on engine running

Customer: replied 2 months ago.
What are some 12v items that only run while the engine is on? IE fuel pump, injectors ect? Are they controlled by ground and not positive? If the fuel pump relay is activated when the engine is running, can I not tap that circuit?
Expert:  Tracer3 replied 2 months ago.

I did not mention that tap as I dont like that location, I am saying you dont really have options for what you want to do, Sure if you want to try tapping into fule pump feed? that will work BUT will only work for 10 seconds whenyou turnj key on and then 12 volts when pump is running,. You atre going outside of design and never said why or what you are hooking up, if you look at this diagram> the blue wire to the fuse box, then the #1 pin at the relay then 12 volts to the pump on the green wire, There just is not anything else when engine is running only

Customer: replied 2 months ago.
There is no source of 12v, that is only available when the engine is running?
Customer: replied 2 months ago.
I can tap into almost any fuse in the inside fusebox for keyed battery voltage in the acc position and engine running...
Expert:  AZTechBrian replied 2 months ago.

Under your dash coming out of your fuse box, there is a purple wire that goes to your audio system. That wire should have power in the accessory and run position. It is only protected by a 7.5 amp fuse. Do you have access to a test light?

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