Looking for 12v power in engine compartment.
Thread Starter
Drifting
Joined: Dec 2002
Posts: 1,426
Likes: 1
From: San Diego, CA Website: ChrisMitchell.us
Looking for 12v power in engine compartment.
I'm installing some spal fans and I need to find a full-time power source and a power source that is only on when the car is on. The instructions say to connect wires to the battery and the ignition, but I cant see a way to get wires through the firewall. So I was hoping to find some place in the engine compartment that would work.
Oh... I cant find my multimeter or I wouldnt even have to ask.
Oh... I cant find my multimeter or I wouldnt even have to ask.
Le Mans Master
Joined: Feb 1999
Posts: 6,807
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From: Hoosier
Cruise-In III Veteran
Re: Looking for 12v power in engine compartment. (77Dream)
I'm doing the same thing right now. Look closely above the brake pedal area and you should see a gromet hole with some harness going into the engine side of the firewall. Clip your lead from the fuse panel and through the gromet hole.
Thread Starter
Drifting
Joined: Dec 2002
Posts: 1,426
Likes: 1
From: San Diego, CA Website: ChrisMitchell.us
Re: Looking for 12v power in engine compartment. (biltogo)
I dont see the gromet going through, all there seems to be is a wiring harness that "plugs" into the firewall (no place for wires to be added).
Safety Car
Joined: Jun 2001
Posts: 4,004
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From: Severna Park Md
Re: Looking for 12v power in engine compartment. (77Dream)
I connected the full time power supply for the fan to the bat. connection at the back of the alt. I connected the smaller hot wire to power the relay to the windshield wiper circut. The wiper wires are easy to get to and splice into with a 3 way connector. On my 73, the hot wire for the wiper is the yellow one in the middle of the harness that pligs into the wiper motor just behind the dist. The wiper circut is on to power the relay whenever the key is in the on position or in the acc. position. It was inportant to me to have the relay powered in the acc. position also since I can turn the key back and run the fan with the engine off to cool down between runs at the track.
Instructor
Joined: Dec 2000
Posts: 178
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From: Twin Lake MI
Re: Looking for 12v power in engine compartment. (77Dream)
On the top of your heater coil compartment is an electrical plug. The dark
brown wire is only hot when key is turned on. It's a good spot for an
electric choke and I suppose it could work for your fans also. Steve
brown wire is only hot when key is turned on. It's a good spot for an
electric choke and I suppose it could work for your fans also. Steve
Thread Starter
Drifting
Joined: Dec 2002
Posts: 1,426
Likes: 1
From: San Diego, CA Website: ChrisMitchell.us
Re: Looking for 12v power in engine compartment. (s79vette)
On the top of your heater coil compartment is an electrical plug. The dark
brown wire is only hot when key is turned on. It's a good spot for an
electric choke and I suppose it could work for your fans also. Steve
brown wire is only hot when key is turned on. It's a good spot for an
electric choke and I suppose it could work for your fans also. Steve
Safety Car
Joined: Jun 2001
Posts: 4,004
Likes: 2
From: Severna Park Md
Re: Looking for 12v power in engine compartment. (77Dream)
Seriously though. The hot for the fan can be connected directly to the back of the alt. This keeps that wire as short as possible. The power for the relay works great spliced into the wiper circut, which is hot in the key "on" and "acc" position. Piece of cake.
Thread Starter
Drifting
Joined: Dec 2002
Posts: 1,426
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From: San Diego, CA Website: ChrisMitchell.us
Re: Looking for 12v power in engine compartment. (Jvette73)
Seriously though. The hot for the fan can be connected directly to the back of the alt. This keeps that wire as short as possible. The power for the relay works great spliced into the wiper circut, which is hot in the key "on" and "acc" position. Piece of cake.
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Safety Car
Joined: Jun 2001
Posts: 4,004
Likes: 2
From: Severna Park Md
Re: Looking for 12v power in engine compartment. (77Dream)
None whatsoever. The wiper circut is solo with nothing else attached. Its plenty strong enough to power the relay. Thats all that wire is for. It just supplies power to the relay so the sender can turn the switch and open the juice from the big hot wire to the fan. The hot wire for the relay draws next to nothing and ive never had a problem with this setup. Plus if you overheat you can pull over and shut down the engine but still run the fan in the acc position.
Drifting
Joined: Jul 1999
Posts: 1,542
Likes: 43
From: Plano TX
Re: Looking for 12v power in engine compartment. (77Dream)
One place everyone overlooks is the battery terminal at the starter. You can't do much bettery than that and you reduce the problems with the fans drawing high current through the original wiring.
You could hook the fans to the back of the alternator, but this can lead to a large voltage drop at the alternator making it work harder than it should. Could also be a problem at night with all the lights on. The alternator outlet wire is only supposed to supply current for changing the battery only. If the fans draw to much current you could have current coming back from the battery through the wire with all accessories on including lights.
Simple fix is to buy a fusible link to slip over the starter/battery terminal. Link is about $2.00 at any autoparts. Then you have a high current source that is out the normal 12 volt circuits. This means you will not put too much load on the old wiring. This also makes a very clean installation.
Dave
You could hook the fans to the back of the alternator, but this can lead to a large voltage drop at the alternator making it work harder than it should. Could also be a problem at night with all the lights on. The alternator outlet wire is only supposed to supply current for changing the battery only. If the fans draw to much current you could have current coming back from the battery through the wire with all accessories on including lights.
Simple fix is to buy a fusible link to slip over the starter/battery terminal. Link is about $2.00 at any autoparts. Then you have a high current source that is out the normal 12 volt circuits. This means you will not put too much load on the old wiring. This also makes a very clean installation.
Dave
Team Owner
Joined: Aug 1999
Posts: 30,995
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From: Ontario
Re: Looking for 12v power in engine compartment. (77Dream)
If you wish to keep the fans on a separate and ignition-switched 30 amp circuit, here is a source. In my 1979 that circuit was intended for the auxiliary cooling fan, an option I do not have. So it was very convenient. You will need an in-line fuse setup.
Drifting
Joined: May 1999
Posts: 1,610
Likes: 3
From: Goulburn, Australia NSW
Re: Looking for 12v power in engine compartment. (paul79)
I went the same way as JVette. Alt for power and the yellow wire from the wipers as the switched wire where it exits the firewall. This puts all the wires on the same side as the radiator opening where you more than likely have your water temp sensor mounted as well as your relay box.
Racer
Joined: Oct 2002
Posts: 396
Likes: 1
From: Coventry CT
Re: Looking for 12v power in engine compartment. (77Dream)
i suggest using the starter power supply.
i wouldnt want my alt. to take the volt drop when the fans turn on.
i have dual spal fans, and never had any trouble with this setup.
i wouldnt want my alt. to take the volt drop when the fans turn on.
i have dual spal fans, and never had any trouble with this setup.
Safety Car
Joined: Jun 2001
Posts: 4,004
Likes: 2
From: Severna Park Md
Re: Looking for 12v power in engine compartment. (JRODDVETTE)
How fast does electricity travel. The speed of light? Very very fast anyway. It doesnt matter where the feed wire to the fan is connected as far as draw is concerned. The bat. wire on the alt. is connected directly to the battery. It makes no difference if connected to alt, bat, starter. when the amp draw from fans kicking on comes, it comes, period. It will effect the load on the sys the same no matter where its connected. In fact, the alt position is slightly better since the wire can be much shorter and have less amp loss due to wire length.
Safety Car
Joined: Aug 2000
Posts: 3,909
Likes: 26
From: Clymer PA
Re: Looking for 12v power in engine compartment. (77Dream)
I just finished installing my dual Flex-a-Lite fans and installed them just as Jvette described. It was more organized and easier to connect the fans to the alternator. :cheers:
It seems to me it doesn't matter what you hook the fans to, you are still drawing amps any way you look at it. I installed mine by only using a toggle switch. This way I can keep the fans off whenever I race down the 1/4 mile.
It seems to me it doesn't matter what you hook the fans to, you are still drawing amps any way you look at it. I installed mine by only using a toggle switch. This way I can keep the fans off whenever I race down the 1/4 mile.
