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Author Topic: Source for Key "on" power  (Read 784 times)
timmycharger
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« on: July 19, 2021, 06:09:26 AM »

I am finally going to address my wiring error from a few years ago when I installed my electric fuel pump harness from Painless.  It uses a relay but has a small yellow wire that is supposed to go to the switch.  I currently have that little yellow wire going to the back of the fuse box on a piggy back blade connector for the radio. Not sure why I did that because every time I put the key in accessory or run position, the pump comes on. 

What is a good under dash source for power only in the key on position? Is there anything on the fuse box itself? Appreciate any feedback.


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Nacho-RT74
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« Reply #1 on: July 19, 2021, 07:57:33 AM »

Anywhere on the blue wire line between ign switch and ballast/reg
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Venezuelan RT 74 400 4bbl, 727, 8.75 3.23 open. Now stroked with 440 crank and 3.55 SG. Here is the History and how is actually: http://www.dodgecharger.com/forum/index.php/topic,7603.0/all.html
http://www.dodgecharger.com/forum/index.php/topic,25060.0.html
comet_666
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« Reply #2 on: July 19, 2021, 07:57:59 AM »

I am looking for the same thing you are actually for my electric fan setup. I assume your using the stock fuse block? I am and I was told that I could use the "heater" blade on the back of the fuse block via spade connector. I don't even have a heater box anymore. Seeing as most of the writing on my fuse block has worn off I'm really not sure where to go with it.
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timmycharger
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« Reply #3 on: July 19, 2021, 10:34:57 AM »

Anywhere on the blue wire line between ign switch and ballast/reg


Thanks, is that right off of the switch harness under the dash? I tried looking in my FSM but I must have pulled out those pages years ago when I was wiring the car as I cant locate them now  brickwall
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comet_666
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« Reply #4 on: July 19, 2021, 10:38:36 AM »

According to my manual the dark blue wire goes to the brake system warning lamp.
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John_Kunkel
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« Reply #5 on: July 19, 2021, 11:19:44 AM »

The 16 ga dark blue wire that feeds the ballast and voltage regulator is keyed power appropriate for a fuel pump.


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timmycharger
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« Reply #6 on: July 19, 2021, 11:33:13 AM »

Thank you!  cheers
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Nacho-RT74
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« Reply #7 on: July 20, 2021, 01:48:59 AM »

According to my manual the dark blue wire goes to the brake system warning lamp.

It is! The ign circuit also feeds that.

Need to mention, the ign circuit will simply trigger the fuel pump, but the source will be coming from batt/alt throught the relay, so don't worry about any extra significant load for that circuit.
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Venezuelan RT 74 400 4bbl, 727, 8.75 3.23 open. Now stroked with 440 crank and 3.55 SG. Here is the History and how is actually: http://www.dodgecharger.com/forum/index.php/topic,7603.0/all.html
http://www.dodgecharger.com/forum/index.php/topic,25060.0.html
timmycharger
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« Reply #8 on: August 02, 2021, 05:56:23 AM »

After working on the car this last weekend, I realized my wiring is not really stock anymore. I have the ammeter bypass and headlight harness upgrades but I also omitted my ballast resistor with my MSD system. I cant find the schematic I used for that but it has been working for over 6 years now w/o issue.

I also am running a 1970s style voltage regulator with a 2 field alternator.

What I ended up doing is taking the key on power from the blue wire that does to the Voltage regulator and that seems to be working. I am not seeing anything strange with the voltage while driving or idling. 

I probably could have used the brake system warning lamp circuit but I couldn't really access it easily as where I took it from.
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Nacho-RT74
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« Reply #9 on: August 02, 2021, 06:48:05 AM »

Voltage regulator is the same source than the stock ballast.

that wire splices somewhere into the underdash harness to feed the cluster brake light and the bulkhead, so if wished to get that source from any accesible point inside the cab you could have taken it straight from ign switch or at bulkhead. After the bulkhead runs to voltage reg, alt field and ballast. It's all the same network
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Venezuelan RT 74 400 4bbl, 727, 8.75 3.23 open. Now stroked with 440 crank and 3.55 SG. Here is the History and how is actually: http://www.dodgecharger.com/forum/index.php/topic,7603.0/all.html
http://www.dodgecharger.com/forum/index.php/topic,25060.0.html
timmycharger
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« Reply #10 on: August 02, 2021, 06:55:59 AM »

Voltage regulator is the same source than the stock ballast.

that wire splices somewhere into the underdash harness to feed the cluster brake light and the bulkhead, so if wished to get that source from any accesible point inside the cab you could have taken it straight from ign switch or at bulkhead. After the bulkhead runs to voltage reg, alt field and ballast. It's all the same network

Thanks Nacho.

Would it make sense for the green wire to the Voltage regulator to also be key on power?
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Nacho-RT74
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« Reply #11 on: August 02, 2021, 07:03:46 AM »

Green wire is either in single field alts and dual field alts the regulated ( pulsating ) signal, BUT:

On single field alts ( older system ) it pulses the positive signal to regulate while the alt gets the other brush constantly grounded, closing the circuit to create the magnetic field into the alt

On dual field alts ( newer system ) the pulsating signal is handled to ground instead, into the regulator, while the constant is positive coming from ign switch. We can say, the green wire handles actually negative. Hence why now the ign switch sends positive to the alt via that blue wire, and that's how is created the magnetic field into the alt rotor

 So, no, the green wire wouldn't be the correct source for any Ign switch source, no matter if using older or newer system, but even less on newer.
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Venezuelan RT 74 400 4bbl, 727, 8.75 3.23 open. Now stroked with 440 crank and 3.55 SG. Here is the History and how is actually: http://www.dodgecharger.com/forum/index.php/topic,7603.0/all.html
http://www.dodgecharger.com/forum/index.php/topic,25060.0.html
AKcharger
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« Reply #12 on: August 02, 2021, 07:56:16 AM »

Ah! Useful info, I have fans on my '72 with same issue...Thanks!
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Nacho-RT74
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« Reply #13 on: August 02, 2021, 08:30:44 AM »

having ammeter, the main source for relays must be taken from alt stud, althougth the positive trigger on relay still will be the Ign circuit.

I have a diagram for it if you wish!
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Venezuelan RT 74 400 4bbl, 727, 8.75 3.23 open. Now stroked with 440 crank and 3.55 SG. Here is the History and how is actually: http://www.dodgecharger.com/forum/index.php/topic,7603.0/all.html
http://www.dodgecharger.com/forum/index.php/topic,25060.0.html
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