I’m looking for advice from the C3 community. I decided to install dual electric fans in my 1979. The previous owner had installed a Champion aluminum radiator so I went to Champion and got their shroud with dual 12” fans and relay. They are low profile type and pull 9A each. Per their instructions, I’m using a single relay rated for 40A max. After quite a bit of wrestling, I got them mounted and like the way they look and it really opens up the engine compartment (see photo below).

Now I am figuring out the actual wire routing I want to use and how to make a nice 2 into 1 wire splice. I plan to power the relay direct from the battery and hope to pick this up at the starter solenoid. I think this will be possible but will find out in a couple weeks when I’m able to move the car to the other side of the garage so I can access the passenger side. The relay coil ground will be through a temp switch in the manifold. I will splice into this wire to install a manual override/test switch.

Assuming all this goes well, the only trick is powering the relay coil. I want a power source that isn’t active during cranking. I think the IGN terminal in the fuse block would be perfect. But it is difficult for me to even see the fuse block let alone work under there and get a wire through the firewall. I am hoping to find something in the engine compartment. I have seen posts where people say to use the wiper motor. I am not so sure because the wire colors on mine don’t match up with what I’ve found in a C3 schematic (photo below). Also, I used my meter to probe the back side of the 3-wire connector on the motor. I put the key in the RUN position and got 12 volts from two of the wires. But I checked about one minute later and didn’t see anything. Not sure what happened there.

So I need a reliable spot to tap into that won’t overload if I need to run wipers and fans at the same time. Any advice?

 

If you are talking about the IGN tab in the fuse block, that is hot during cranking. Lots of folks using this tab to power HEI dizzys, so definitely hot during cranking.
That’s why the suggestion of wiper motor - it drops off during cranking.

Edit: your relay coils will add very little current to whatever circuit you select, so not too much worry about overloading, but it doesn’t hurt to check…

 

Thank you. Makes sense. Any advice on determining which wire to the wiper motor is correct for this?

 

This diagram might help. Myself, I run two relays for the dual fans. I wanted to kill the always on low setting for the interior blower fan but still be able to use it when I wanted too. I also needed an IGN trigger for the fan relays. So I discovered that the TAN wire in the connector for the blower motor that sits on top of the AC box in the engine compartment controls the always on low speed fan setting. I pulled that tan wire which kills the always on blower and used it for the IGN trigger for my fan relays and it works like a charm. All other fan switch settings continue to work as designed. Good luck and hope this helps.

 

Thank you. So when I turn the key to RUN (without starting), that humming noise is a always on low setting for the fan controlled by that tan wire? And when you disconnect it, you can still operate the fan manually? Do you know if it's HOT during cranking? Is there a reason you'd want the fan to always be on? Someone must have thought so.

 

Yes, disconnecting the tan wire will still allow all other fan settings to work as designed. I believe the always on blower was part of the ventilation system but I found it annoying as heck. Not sure if it's hot during cranking but if it was, it would be very little power. I've run this way for years with no issue. Why do you need it to be unpowered when cranking?

 

Maybe others will tell me I am overthinking this, but the reason I wanted it unpowered during cranking has to do with restarting an already warm engine. The temp switch would still be grounded. So the fans would be starting up right as you’re cranking. I understand the inrush current is about double. Maybe this isn’t a big deal since the cranking time should be pretty short on a warm engine. Anyone have thoughts on this?

 

I went a little overboard- I used a Hella delay/timed relay- you can adjust from 1-900 seconds as far as delay.

I used it on all my heavy draw stuff- that way the engine gets up to idle - alternator is recharging the battery from the starting- then the other stuff turns on.

Then I also used the relay to delay off - power windows-headlights- electric parking brake- so they'll stay on a bit after you turn off the the ignition.

 

Wow Richard you really like your relays ...Impressive. Sorry blue thunder, I run an LS so I have the fan overrun turned off so no fans unless the engines running. I run two relays too so I can control the fans independently. Nice thing about a computer is you can control almost all aspects of the engine, even the fans, with a few clicks of a mouse. If you're up for the wiring, Richard454's setup may be overkill but is an elegant solution. Also, there are PWM controllers which allow for variable speeds based on temp range as well as soft start features which prevent the fans from both coming all full tilt at the same time. Regardless, unless you're hot starting a lot, and you've wired it properly, I doubt it's going to be any real issue. I know people, right or wrong, wire dual fans to always on and it doesn't seem to be a problem even though it is kinda back woods rigging....

 

Thanks guys, you’ve given me some great advice. Richard, wow, that is next level. Would love to see it. I think I’ll keep mine a little simpler but am confident now that I don’t need to break my back crawling under the dash.

 

FYI, I didn't see it mentioned so the ACC circcuits are the ones that are not on during cranking, only when key is in the ACC or Run positions. IGN circuits are on in the Run or Start positions.

 

here is electrical 79 ignition etc.. i will try to attach entire electrical as pdf but for now if it does not go thru a pic hacked together. PDF is 30 MB