what wire can i use underhood to hook up the wire from the fans so i have power when i turn on the key Thanks

The blue wire at the ballast resistor is keyed power but you can only use that to energize a high-current relay to carry the load of the fans.

you'll need to know what the fans draw current wise for two reasons, 1. make sure your charging sytem can handles the addedd load and 2 so yo know what size fuse and relay is needed

A diagram I made quite ago for a full dual fan setup, including the option for the extra cooling when A/C is on. Using temp switches.

Nice diagram nacho
He still needs to check his current draw and charging capacity

I installed one large aftermarket electric fan on a drag only car years ago and found that it would draw 70+ amps on startup initially
To much amp draw can melt overloaded, to small, wires real quickly

A little more info on how you have or plan to have this fan wired would be helpful. A relay switch and possibly a breaker switch is highly recommended to help isolate the load on your electrical / charging system.

The relay has four wires: 1) 12v constant from battery 2) 12v remote-on (powered by key switch) 3) Ground 4) Output to Fan. If you run a simple breaker, it goes inline on the 12v constant wire from the battery to the relay.

The 12v remote-on source you're looking for can be found in various places. Most fuse panels have extra tabs on a few of the 12v sources that only have power when the key is in the run position. You can simply run a wire from one of these 12v sources to your relay switch. Since this wire only triggers the relay switch "on" they draw very very little current and don't need to be a heavy gauge wire.

Fans can draw a lot of current. It's important that you're running a relay meant to handle the load of your fan. Additionally, an electric fan may require an alternator that has an output greater than stock to keep your battery charged.

-Dan

Many good replies already.

To get the full benefit of an electric fan addition, and most $ return on investment from fuel economy, there should be a switch to turn the electric fan off at highway cruise to lessen un-needed air coming in through the grille and going out the bottom of the engine compartment, then flowing against the rough under carriage.

With the fan turned off the engine coolant temperature should be allowed to rise to at least the 220 to 240 degree F level which also improves part throttle engine efficiency, and heats the air up flowing through the throttle so the throttle blades will open up, improving manifold absolute pressure, and lessening the amount of ‘negative work’ the engine produces dragging pistons down against a vacuum on the intake stroke.

Either a knowledgable human driver, or a well written microprocessor program, should decide when to turn this switch on/off.

On top of this recent Ram trucks have grille shutters to lower harmful airflow at part throttle highway cruise.

I use a pulse width controler from Auto cool guy, works awesome, CLICK HERE

That is why the load for these should never be off the alternator stud. Worse on older cars with inductive ammeters and failure prone bulkhead connectors. Alternator should be wired with protection direct to the battery or a buss connector. All loads should be off that point and correctly set up with relays and fuses.

I have one of Autocoolguy's controllers on my 451 Dart, with Ford Contour electric fans. Pricey but works great.

With ammeter, all loads must be sourced from alt side of the charging network, never from batt

You are so wrong. Anyone that wires these old cars off the alternator stud with old wiring and connections is a hack.

I used this on my car, thought it was a good price and saved some time.

https://leashelectronics.com/products/dual-70-amp-relay-board

I have dual electric fans. One is wired in and thermostatically controlled to come on automatically through the Racepak. The second one is wired into my overhead switch panel mounted to the cage halo bar.

Two conditions to get it right.

Once you add accesories as an upgrade on your car, i.e. electric fans, the alternator must be upgraded accordingly. Stock configuration for a correct ammeter reading is everything must be sourced from alt side. You need just to check a factory diagram to prove this is a must.

So the conditions if keeping ammeter on car to be correctly sourced are:

-Everything must be sourced from alt side
-alt must be upgraded accordingly to the new accesories to keep the right reading and the loads going throught the correct side.

Several reasons why wiring on Mopars are a weak spot and this is on 70% of times owners/mechanics fault by the unkownledgement of how the system works.

The alt provides what the car and its accesories requires to work and tries to keep the batt fully charged, nothing more, but less is not capable.

If you source anything on batt side, more load will go through the stock wiring, bulkhead, ammeter etc… like if the batt will never get fully charged. So if you source, on this case, electric fans correctly on alt stud, the load the alt will supply to source them, WON’T EVER RUN through the stock wiring but straight from alt to the fans relay setup. BUT if you source them on batt side the required load to feed them will be stressing unnecessarily throught the stock system and amm will be constantly on CHARGE side.

Which is true, bulkhead is a weak spot, and stock alts are tipically unable to keep the batt charged at iddle, hence why when revving up the engine, the ammeter senses CHARGE. This is increased with loads hooked up on batt side as mentioned.

The only moments weakness of the stock system becomes critical sourcing CORRECTLY the added accesories on alt side is when the alt is unable to source most of the required loads (or engine is off, so does the alt ) and battery becomes on the constant main source. This is the moment when the ammeter becomes on a dancing gauge going back and forward along with engine revs. The more load going back and forth along the charging system, the more heat is able to get and this is the moment becomes on a dangerous stage.

Since the beginning EVERYONE began to source added accesories on batt side. This along with the weak bulkhead spot (which is true) and the unneficient stock alts at iddle is what got our Mopars burning wiring along the years. Add to this, ppl “upgrading” batteries with more reserve capacity to hold added accesories, which it took MORE time to keep them charged by the uneficient stock alts… so more stress to the system.

So in conclusion:

Hook up the fans on alt stud and upgrade the alternator are the correct way to proceed to keep safe the wiring and ammeter and EVEN THE BULKHEAD conector, because bulkhead won’t get ever this load correctly soorcing the fans. But is true some easy wiring mods are advice just in case, like save the bulkhead connections with some paths and wiring upgrades… which has been already shown and discussed in the past on several threads when talking about alt upgrades and those who thinks the ammeter bypass ( or the jumpong wire between alt and batt ) is the solution. No need to jump out batt with alt, which bypasses the amm reading. And with the correct procedures, the ammeter will be still safe and reading strong and correctly

Being there done that, on a driver ( A REAL DRIVER ) 74 Mopar on a heavy transit city.

Which is also true is when proceeding with any add on or upgrade, the related system must be correctly checked to be sure if will survive to the new part or upgrade.

Wrong. You show me one car or truck that the loads are sourced off the alternator stud. Show me do not avoid this direct question with mambo jambo. Next tell me with your VooDoo alternator stud taking all the add on load what happens when the alternator quits charging??? Where does that load no go? Answer that. There are right ways to do this and yours is not it.

ALL CARS ( not just Mopars ) with ammeters are sourced from the alt side of the ammeter... no matter where... if straight from the alt stud, the ammeter stud or an intermediate splice... as far the loads are taken from the alt side of the ammeter.




diff stuff you tipically never see anything hooked up to the alt stud because splices are down the tape harness, but for new adds without untape the harnes, the two points to source correctly new accs are amm stud or alt stud

You never answered all the questions.

unfortunatelly the thread where I explain all details about upgrades of the charging system got missed the attachments due a forum software upgrade. Will work on recover those, but for a while:

https://www.forbbodiesonly.com/moparforum/threads/poll-about-ammeter-reading.198930/page-3 ( linking to the 3rd page whre I begin to put pics about how the charging system works )

http://www.heritech.org/cuda/Charge.html

questions are answered on dozens of threads where this has been discussed. BUT just begin with those. I can post many but don't wnat to highjack the thread (more).

BTW, diagrams are mine... which I made back in 2007... weird you haven't seen these also on Moparts.

all answers you posted are on diagrams and their explanations...