Not sure if this is the right place but I came to this site cause I think alot of people run Mark VIII fans here. Im going to be installing one in a 72 nova. But Im just alittle confused on the wiring.

I am just looking for the simplest way to wire it up. Cant I just run a than fan from a 75amp bosch relay, and a in dash switch to the relay to activate it? (possible ad a thermal switch but that would be simple) No diodes or anything fancy like that?

Also Do you think a 94 amp alternator is enough to run/start the fan?

One last thing, any one know which wire/pin corresponds to ground/power/signal(speed)

Thanks

 

Not sure on the wiring, but yes it can be done very easily.

Get a standard 40 amp four pin relay available at any parts store.

Get this T-stat switch, which can go in either head's water port, or in the intake manifold in a heater hose port.

http://store.summitracing.com/partde...5&autoview=sku

I would suggest use an IGN source to trigger the relay, and power the relay from the battery. Ground the relay to the T-stat switch above, and then run your wire from the relay to the fan. Then ground the fan, somewhere short and close to the fan, keeping the gauge of the ground the same as the power wire.

I would suggest an inline fuse in the power wire before the relay.

As for the switch, just run the IGN or ACC trigger wire into the cabin, and back out to the relay. When it's looping through the cabin is where you can wire in a switch if you want to override it, but the T-stat switch above will only contact the ground for the relay when it gets to 185, and it'll switch off again at 165.

I did this to one of my dual fans. The other is constant with the IGN.

 

An interesting question. DB has a good grasp of it. to be plainer- on the control side- from the IGN tab in the fuse box, to the inside switch, to the + side of the coil on the relay, to ground from the - side of the coil of the relay. Now with the ign switch on, throw the switch, a friend with his hand on the relay should feel it click. You can replace the inside switch with the temp switch DB has listed if you want.- or wire it in parallel, for more control.
Now for the power side. I differ from DB on this, I think you should run your power wire, (I would recommend 8 gauge, but 10 will suffice), direct from the alternator, because it will be the alt that will be supplying the current when the engine is running with the fan cooling it, so it will feed the current directly into the fan. You will need some 10 gauge and some crimp rings, crimp the ring on the wire and use the nut to hold it on the Alt output stud. from there go to any side of the contact on the relay, then from the relay to the fan, then from the fan, WITH the same gauge wire or better, to a solid ground, i Would recommend a frame or frame welded part, sand down till you see metal, crimp a ring connector on this, coat it with electrical grease, and torque it down tight. That will work.

I think you should upgrade to a 140 alt.

 

The Mark VIII fan has 2 speeds - 3 wires. The outboard black lead (uppermost pin on the motor if you do not have the pigtail) is the ground (negative). The blue lead (lowermost pin on the motor) was used to activate the fan when the AC was turned on (positive). The center lead (also positive) is black. It was activated by engine temp. I understand that using the black/black combo will give you a higher fan speed than the black/blue combo.

 

If the fan is pulling current directly from the alternator then the alt will never see the battery's actual charge, and the internal voltage regulator will not be able to properly keep the car's electrical system at a specific voltage. By wiring the fan to the battery, or even the starter lug from the battery cable, the alternator will sense actual system voltage and keep things regulated properly.

 

The alternator is internally regulated, so it will charge the right amount either way. The voltage at the alternators bat + terminal will be battery voltage whether the fans are on or off. Running the power wire to the alternator will just make it so the current for the fans doesn't have to travel through the original alternator wiring if the engine is running.

 

Some 2 speed, and some variable speed.

Here's the link thread where it was discussed.
http://forums.corvetteforum.com/show...ight=mark+viii

And here's what I discovered for my fan:

Following discussion with Rastadr, who owns a Mark VIII fan, and inspection of my new Mark VIII fan, it appears that the 1998 Mark VIII fan, part numbers RF-64 and/or F8LH-8C607-AA, only has leads connected to the 2 outermost male terminals.

I opened up the inspection cover and it is readily apparent that the center terminal, which extends into the area beneath the inspection cover, is not hooked up to anything. It's just sitting there, brand new, with no leads attached.

After surfing for awhile it seems that the 98 fan was a variable speed fan controlled by the Lincoln powertrain system. SO, I guess I'm ok, I can either run it from the ECM (it'll run at full speed each time it's started) or I can buy one of them variable speed controllers.

 

I have a '95 Mk. VIII fan, and it only runs at one speed without the external controller - I tried the ground and outside wire, the ground and inside wire, and the ground and both + wires together - nothing changed the speed one bit.

 

but not sure of my fan year!