Starter relay 4 speed,

[5.7 hemi]

Is there a way to get 12v switched from the starter relay? I have the battery out and most of the dash disassembled so I can’t hook up the battery to check.

 

[mopar 3 B]

Battery charge + to relay - to ground

 

[5.7 hemi]

Let me rephrase, which stud/terminal can I rob off of for 12v switched, if any?

 

[gkent]

12v switched at the relay is only switched by the ignition key. The relay has heavy 12v in and switched heavy 12v out to the starter solenoid which is activated by light 12v from the ignition switch.

So for 12v switched you could take it off the small terminal if you have the ignition switch wired OR you could take it off the heavy lug that goes to the starter. But without the ignition switch wired you're dead in the water.

 

[5.7 hemi]

Everything is wired correctly, car runs perfectly, I’m adding electric fans and they require a 50 amp automatic resettable circuit breaker, and they want it to go to battery positive. But that means they can come on at anytime, so I want it on “switched” power.

Just need to know which stud/terminal is actually 12v switched on the starter relay.

 

[5.7 hemi]

I re-read the above post and I’m think I understand it. The terminal with the screw is the switched 12v?

Please forgive me, I’m not electrically inclined, but learning.

 

[gkent]

I would give the fans full time power. When you shut the car off hot you want the fans to continue to run (just like many modern vehicles).

 

[5.7 hemi]

But then they can also run when the car is sitting in the garage, outside and whenever the temp is hot. Don’t laugh, it has happened.

 

[HT413]

That big stud on the relay is a direct connection to the battery so will be hot all the time, regardless of ignition switch position.

I ran the fans to that stud (relocated my battery too) so they have power all the time. But they won’t come on unless the controller tells them to, so just wire the fan controller to the ignition switch run circuit.

 

[HT413]

I would give the fans full time power. When you shut the car off hot you want the fans to continue to run (just like many modern vehicles).

I dunno, seems it would only help if the water pump was also running?

 

[5.7 hemi]

Yeah, I knew that, and figured out that the starter relay only has 12v when cranking. So I’ll run another wire from my fuse panel for my 12v switched.

 

[gkent]

I dunno, seems it would only help if the water pump was also running?

Not really. Since the thermostat will stay open the hot water can still flow due to convection - until its cool enough to close the thermostat and by then the fan thermostat will probably have reached its lower limit too.

But then they can also run when the car is sitting in the garage, outside and whenever the temp is hot.

There is no harm in wiring the fans to full time power. Having them come on in a warm garage - c'mon, that's an old wive's tale right ?!?! If it gets that hot outside either the controller is set too low or you'd better worry about the planet burning up.

The fans should only come on to maintain a temp in the 190 to 212 range.

 

[5.7 hemi]

It’s happened before, some owners of the Derale fans, 65roadracer being one of them, had the fans come on in his garage, no bs! They weren’t at full speed, but still were drawing power.

Since then Derale has come out with a different sensor and I’m sure I’d be fine, but better safe than sorry.

 

[HT413]

This really isn’t an issue unless you leave your ignition switch on and park your car in a wood kiln.

Most controllers are wired to switched ignition for the control relay AND to a temp sender AND direct to battery for fan power. (every one that I’m aware of, though certainly I don’t know them all). This way fans can only come on when ignition switch is on AND the fans are being called for by temp sensor.... and when the relay makes, fans have that direct feed to the battery for main power draw.

Far as wiring, the controller should have 4-6 wires. 2 for relay coil, 1 or 2 for temp sensor and 2 for main fan power.

The power side (fan) has 2 wires- 1 that goes to the battery / starter relay stud (constant power), one that goes to the fans.

The relay coil has 2 wires - 1 goes to switched ignition / run circuit and the other to ground.

The temp controller then has 1-2 wires that come in from the temp sender.

 

[HT413]

It’s happened before, some owners of the Derale fans, 65roadracer being one of them, had the fans come on in his garage, no bs! They weren’t at full speed, but still were drawing power.

Since then Derale has come out with a different sensor and I’m sure I’d be fine, but better safe than sorry.

Its possible only if the controller uses one power wire for both sides of the relay... the control side and the main power (fan) side. Post a pic of the wiring diagram and I can tell ya.

 

[5.7 hemi]

Derale wants power and ground straight to the battery with an in-line resettable 50 amp circuit breaker.

I did find a few wires I’m not using at my fuse panel which are switched, so I’m good.

Thanks to all who helped me with this.

 

[HT413]

Derale wants power and ground straight to the battery with an in-line resettable 50 amp circuit breaker.

I did find a few wires I’m not using at my fuse panel which are switched, so I’m good.

That’s all fine, but the question is this. Does the controller have 2 power taps or 1? If 2, you can wire the fan to the battery and the relay on the key.

If only 1, meaning the relay taps off the main fan power, you’re probably stuck going straight to the battery through the supplied 50 amp breaker... unless you’re lucky enough to have a circuit on an aftermarket or racing wireharness that has a 50 amp capacity.

 

[5.7 hemi]

1 power, 1 ground. Here’s a pic of what it looks like.

 

[HT413]

Yep, that’s all she wrote.

If I’m right, that override is optional to be wired to a toggle, which when on will override the controller to turn the fans ON, not off. Id guess the people posting about the fans coming on with the car off are referring to that. They’d run slower of course because they’re only at 12v vs the 14-14.5 they’d see while running.