12v Keyed power source - dumb question

[pcguy2u]

Nearing the final stages of my Chevelle restomod project (link in the signature) and I need to find a keyed power source. I know that most fuses should test as keyed, but my testing shows that to be questionable.

The above coming from someone who is very familiar with computers and electronics. This one has me stumped a bit.

My assumption in this (yeah I now about them) is that the key activates a relay that energizes the fuse panel and the appropriate fuses. Is this really how it works?

My testing shows direct continuity (a short if you will) between most all of the fuses, including those you know don't have power when the key is in the off position, that you know don't/shouldn't have power when the key is off, like the windshield wipers for example.

The reason I am testing with the key off is that I'm not ready to energize the whole wiring system. but I need to wire up the new rear window motors and the Camaro donor didn't/doesn't have any rear windows that open.

I understand that the BCM has some degree of control of all this, but I know I'm missing something here. If the power is constant at the fuses and the BCM is where the control is for powering up the circuit, does that mean you need to connect to the output side of the BCM, or? This situation is true for the under hood fuse panel and the rear fuse panel. Have checked the driver's side under dash panel yet.

Perhaps you guys can steer me in the right direction?


TIA, Nick

[pcguy2u]

Bump

[HadA68]

I don’t know if this will help or not but I recently installed an aeroforce interceptor gauge and AFR kit. The AFR kit comes with a controller that requires “accessory” power. Since I installed it under the dash, i decided to tap into the driver’s side fuse panel. I had installed some other things into that fuse panel so I had to hunt around a bit for a good source. In my hunt I used a multimeter and turned the key on and off and the power to those “accessory” fuse definitely went dead when the key was turned off. I don’t know for sure but I would say your assumption about a relay ( or relays) supplying power to those fuses is probably a good one. So could you use one of the accessory power circuits?

[pcguy2u]

Thanks for that - did something similar. Since I mounted the rear windows controls/switches on the drivers side of the center console I decided to use both of the accessory power outlet feeds - they both located on the console and the wires pass right by the window switches.

The reason I used both is that the operation of both rear windows at the same time requires a 30amp fuse and each of the accessory power outlets only have a 20amp fuse.

I never did answer the question about why these circuits (all the keyed circuits) test with continuity to the battery positive cable with the battery disconnected. It must be some relay that transfers power when the battery is connected. That kind of doesn't make sense because it means the relay is drawing power when the car is just sitting somewhere not being used. Of course that helps to understand why the batteries in these cars cannot sit for extended periods without a battery tender...

The good news for my project is that after having taken the donor Camaro apart (down to the last plug and nut and bolt) and reassembling it in the Chevelle, the electrical system is functioning as designed. I'm now past the hurdle of gaining some confidence in the end result.

I started out by connecting a 7amp fuse in series with the positive battery cable and I can now even turn the key without blowing that fuse.

Thanks again,
Nick