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Thread: Switched to Power - wiring question

  1. #1
    another classic car guy EricB's Avatar
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    Default Switched to Power - wiring question

    Hi all,

    Long time no talk... Hope everyone (and their Zs) are doing well.
    So let me preface the following by saying that even back in engineering school I already had a certain aversion to circuits and wiring. Things haven't improved since...

    So I need a hand, please.

    I am looking for a good switched to power source to run a couple accessories. I'm guessing that where I had them before wasn't the best place as I had some recent electrical problems, which made me miss JCCS07 unfortunately. I want to do it right this time.

    1 CSR water pump draws 5.8amps and is fused with a 15A fuse
    1 PermaCool 14" fan draws 9.5amps and is fused with a 30A fuse

    I'm thinking about wiring the water pump in parallel off of the 73 electric fuel pump, right next to the fuse box. Here's where I get confused:

    _ If the power that supplies the 73 electric fuel pump fuse is fused at 20A, and I add a new circuit in parallel which pulls almost 6A, do I either have one larger fuse supplying both circuits, or do I have each circuit have its own fuse. And then should I go a size up on the wiring upstream of where these circuits split from one another to handle the extra draw? How far upstream do I go? just to the fusebox or further?

    If this is an ok place to do this, or is there a better place?


    _ For the fan, I was thinking of wiring it direct to the battery so that the fan keeps spinning while the engine is hot even if I switch the ignition off. That's the way I used to have it, is that a bad idea? If I don't, then I need to find another switched to power, can I go in parallel (again) to what's above?


    Can I get a little help on this?
    Thanks in advance guys...

    -e



    PS: I also have an E12-80 dist & an internally regulated newer distributor, I know the 73 has some wiring/relays which don't apply anymore since I took out some of the stock electrical components. What can I safely remove/simplify? Or is this a better question for a new thread?

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    Banned User V8-240Z's Avatar
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    Your doing the same thing I am doing with my small block 240Z conversion, except I have the Meziere water pump. I use 2 continuous duty relays one for the fan and one for the water pump and a bridge diode so when the engine is off and the fan is running so is the water pump. At first I had some glitches in my wiring and relay problems with the standard small relays. The secret is pulling your power off the battery for both and not from the stock wiring.

    I use the ignition circuit for the water pump relay but the fan is run off of a temp activated switch and can run anytime the temp hits 185.

    I found out the hard way, too much depends on the pump and fan and things go bad real fast if they quit.

    Dave

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    Registered User Nissanman's Avatar
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    another classic car guy EricB's Avatar
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    Dave,

    Both the water pump and the fan came with relays, so you're right our set-ups are probably pretty close to identical... I've got both relays wired up as per the instructions, I'm just not sure where to connect the switched to power wires on the car itself...

    Thanks in advance,

    -e

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    Nissanman has laid it out as well as possible I think. His diagram shows a totaly independant add on circuit, that is not reliant on any of the existing wiring. He shows a new cable coming off the battery to a new fuse block. It is protected by an inline maxi fuse. Depending on what your needs are, you can run as many individual circuits off this as your maxi fuse is rated for. His diagram shows 3 circuits, but if you need more simply add another new cable from the battery with another maxi fuse. These will feed the new fuse block which protects the individual circuits. When updating an older vehicle with these add ons it's important not to tie into existing circuits.
    Your electric water pump and fan(s) should ideally be controlled in this manner. The relays should be triggered by a ground signal from thermostat switches. This way they will cycle on & off automaticaly at the right times. Dave has the additional feature of the water pump shutting down when the ignition is turned off. To accomplish this all you need to do is feed a 12V ignition run wire to pin 86 of the water pump relay. In this manner the relay is still triggered by the thermostat switch but the ignition/key must be in the run position, in order for the water pump to run. If you are still unclear how to do this let me know and I can draw up a diagram for you.

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    another classic car guy EricB's Avatar
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    I've got the same thermostat switch as Dave mentioned.
    Probe in the radiator set for 185deg

    I totally agree about the relays - got those... good to go.
    I was just confused as to where to tie in to the switched to power...
    the main power lead is already coming off the battery

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    I tapped directly into the black/white wire coming from the ignition switch. I then ran a line from this connection to a power distrubition block, where four wires then run to four relays (one for my EMS, one for my coil on plugs and injectors, one for my fan, and one for my fuel pump).

    "_ For the fan, I was thinking of wiring it direct to the battery so that the fan keeps spinning while the engine is hot even if I switch the ignition off. That's the way I used to have it, is that a bad idea? If I don't, then I need to find another switched to power, can I go in parallel (again) to what's above?"

    If it's a hot day and I want to make sure my car does not boil over when I turn it off, I turn the key back to the "ON" position and let the fan run until it shuts off. My fan is controlled by my EMS and is set for 180 degrees.
    Last edited by ktm; 11-02-2007 at 12:27 PM.
    -Bo

    1972 240z - Not original and still not done.
    "Something wicked this way comes...."

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    Banned User V8-240Z's Avatar
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    For my 71 I have a fan switch in the intake manifold of the V8 that is the ground side of the relay, The fan is independent of the ignition switch and will run with the ignition switch off. I use a diode to back feed the electric water pump so it also runs when when the fan is on and the engine is off. A fan switch in the radiator is only seeing the radiator temp, but the fan switch in the engine sees the entire system especially when the electric pump is running when the engine is not. The longest my fan runs once the engine is off is a couple minutes and does not come on again until the engine is running. The fan will always run longer than it has to once the engine is off if the fan switch is in the block and there is no water circulating in the system.

    I started out with the standard automotive relays for the fan but after burning up a couple of them I switched to a contunuos duty relay pictured below. Its not a starter solenoid, its draws 1/2 Amp across the coil and is rated at 100 Amp and has large contacts. They vary widely in price with the more expensive ones having silver contacts that are not necessary for a fan.
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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    Last edited by V8-240Z; 11-02-2007 at 02:14 PM.

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    Bo, that must be a little inconvenient, having to turn the key back on to run the fan. Fan relays cycle on and off constantly and are probably the hardest working relays in a modern vehicle. I can understand upgrading them. I’ve cooked a few of them. My Mopar has a CSI (now CSR) pump and two electric fans. One fan is controlled by a 185 degree thermostat switch and the other by a 210 degree thermostat switch. Only the 210 degree controlled fan will run after shutdown. There are two schools of thought when it comes to running an electric water pump after the ignition switch is turned off. A crank belt driven water pump doesn’t circulate the coolant after the engine is shut down, so why should an electric? Is there any benefit to having it run on? The engine cannot get any hotter after being shut down. Circulating the coolant will only cause the fans to run longer after shutdown. This isn’t an argument I’m making, just one I’ve heard. My thought is it can’t hurt, although I don't run mine after shutdown.

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    Banned User V8-240Z's Avatar
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    Quote Originally Posted by geezer
    There are two schools of thought when it comes to running an electric water pump after the ignition switch is turned off. A crank belt driven water pump doesnít circulate the coolant after the engine is shut down, so why should an electric? Is there any benefit to having it run on? The engine cannot get any hotter after being shut down. Circulating the coolant will only cause the fans to run longer after shutdown. This isnít an argument Iím making, just one Iíve heard. My thought is it canít hurt, although I don't run mine after shutdown.
    These are good points, my thought was that the only reason the fan is on is because the fan switch on the engine or radiator says the the temp is above 185 or 210. With out the pump running all that is being cooled is the radiator. With the pump running after shutdown both the engine and radiator are being cooled. With my 240Z the fan and pump never runs more that 2 minutes and once its shut down has never restarted until the engine was running.

    I have it wired for 2 fans but never installed the second fan. The only fan I have is a pusher in front of the radiator.

    On your Mopar what did you use for the 210 degree fan switch. I have a 185 but could not find a 210 that was pipe thread to fit the manifold.

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    If I remember correctly I ordered both switches from a Spal dealer online. It was a package deal. I also bought a Howe radiator from them. I'll see if I can turn up more details. I didn't know they were hard to find. The 2 minutes of runtime you have is OK anyhow.

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    Dave - Ha! The automatic censor won't let me link this, but go to www.rodneyd!ckman.com & scroll down to Low temp radiator fan switch. They have the 210 degree switch with the proper thread for $19.00 & $3.00 shipping.
    Last edited by geezer; 11-02-2007 at 08:00 PM.

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    Registered User Walter Moore's Avatar
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    I think that with our car's older style "cold in the bottom - hot out the top" cooling system there will be some coolant circulation just by convection so long as the fans are running and cooling the fluid in the radiator.

    In either case pump running or not, as soon as the thermostat closes all circulation stops.
    '71 240Z, Because any fool can drive fast in a straight line.

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    Ron, it is a little inconvenient but I get over it. My engine management system controls my fan. It switches the relay ground based on the temperature I set. I am running the Flex-a-lite 210 dual slimline electric fan. I can set my temperature point, so if I am finding that my fan is cycling on and off a lot, I can drop the temperature or raise the temperature a bit to reducing the cycling.

    While the engine may not get any hotter, the coolant certainly can and does. This is what I meant by keeping the coolant from boiling over. The moment you shut off the car, the coolant stops flowing yet the head is still the same temperature. Since the coolant is no longer flowing and the car is not moving, the coolant temperature starts to rise.
    -Bo

    1972 240z - Not original and still not done.
    "Something wicked this way comes...."

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    Quote Originally Posted by Walter Moore View Post
    I think that with our car's older style "cold in the bottom - hot out the top" cooling system there will be some coolant circulation just by convection so long as the fans are running and cooling the fluid in the radiator.

    In either case pump running or not, as soon as the thermostat closes all circulation stops.
    The thermostat will not close until the engine has cooled down. Relying on convection is why the fan will repeatedly turn on and off once the engine is off. With the electric water pump running after shut down the engine is quickly cooled down and the fan only runs once for a surprisingly short time.

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