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I am troubleshooting electric fan wiring. The fan is currently wired to turn on with ignition on and it works fine.

When I unwrapped fan wires, there are two wires, one connected and one was not. The connected wire measured 7.5 volts and the unconnected measured 4.5 volts. I assume this fan is 2 speed, but only wired to operate at one speed (high). My question is what do I do with this second wire? If the circuit runs in series, cant I just ground this second wire? Wouldn't this put fan in low speed permanently?
 

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Wylie, TX - Lee
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I assume this fan has 3 wires one of which should be tied to chassis ground. My guess is the fan is only running at slow speed. To get full speed both wires should be connected to the battery via a relay and fuse.



The fact that you are only seeing 7.5 volts on the connected wire is odd. This voltage should be closer to the battery voltage. What was your ground reference when taking voltage measurements? The 4.5 volts on the unconnected wire is probably meaningless as you are most likely just seeing a voltage produced inside the fan from the mutual inductance of the low and high speed windings when the fan is spinning.
 

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I assume this fan has 3 wires one of which should be tied to chassis ground. My guess is the fan is only running at slow speed. To get full speed both wires should be connected to the battery via a relay and fuse.



The fact that you are only seeing 7.5 volts on the connected wire is odd. This voltage should be closer to the battery voltage. What was your ground reference when taking voltage measurements? The 4.5 volts on the unconnected wire is probably meaningless as you are most likely just seeing a voltage produced inside the fan from the mutual inductance of the low and high speed windings when the fan is spinning.
Thanks Lee,

I honestly dont see any relay or fuse. It looks to me like the orange wire comes straight from the engine bay circuit box (??) and connects to the fan.

My ground reference used was the battery.

I agree there is a third ground wire. I just didn't expose it yet.

I plan to replace radiator and fan, but just hoping to delay it for now. Is there something I can do to make this "electrically safe" or is this just a hack job by previous owner.
 

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Wylie, TX - Lee
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It does sound like a hack job, I think I would start over by removing the existing fan wiring. Cooling fans typically draw around 20A or more so taping into the original fuse block for power isn't a good idea. What's probably happening is that the current fan connection is overheating and becoming resistive which is causing the ~4V drop that you are seeing. Given you reported that the wipers only work when the fan is disconnected, I suspect that the fans are being powered from the wiper circuit which is really a bad idea, since that wiring is only using 18AWG wire which is way too small for a cooling fan.

So instead use a relay connected from the battery and use the existing ignition 12V tap from the fuse block to turn on the fan when the key is turned on. Then from there you can decide if you want to run the fan at high or slow speed by simply connected one or both wires from the fan to the relay. I would use 10AWG wire for the battery to relay to fan connection and 18AWG is sufficient for the relay trigger.
 

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Although there is a new AAW harness/fusebox, I have known there were electrical problems (slow battery drain (sometimes), clicking near headlight/wiper motor switches when connecting battery (replaced headlight switch--no change), rs hideaway lights not working, etc).

I have been reviewing electric fan wiring diagrams and what you said makes perfect sense. Maybe correctly installing a relay and fuse will get me going in the right direction with this cars electrical gremlins.

Thanks again for your input...
 

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Blitzer454 is dead on with his advice. An E-fan arrangement should ALWAYS use a relay, due to its high amp draw. I'd even recommend a controller to operate it. There are one and two speed controllers that you can purchase, and the good ones come with relays and wiring, along with wiring diagrams to assist in wiring it properly.

Flex-O-Lite sells a good one. They are pricey (in the $100.00 plus range), which might be why folks don't use them. I ask myself, why would I skimp on something important like a E-fan controller on such a classic car?
 
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