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Old 03-23-2012, 09:35 AM
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Common Grounding Stud in Engine Bay

I noticed the negative wire (14 gauge) on my 15 inch fan has melted the flexible plastic conduit at the spade connector. The spade connects to a 12 gauge ground wire run to an engine block bolt.

I am wondering if a heavier gauge ground wire (10 gauge) run directing to the battery negative might give a better ground, and also use ring connectors on the fan negative and 10 gauge ground wire, mounting them to a common ground stud near the radiator.

For the stud, do I need a isolated ground terminal or how about just a bolt through a hole in the sheet metal somewhere in the engine compartment?

So the stud (bolt) would be in contact with the sheet metal as well as the two ring connectors. This is a carbureted car not on a computer.

John

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Old 03-23-2012, 09:48 AM
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Sounds like a bad crimp or connection. A heavier wire might help, but a ring connector with a good crimp will most likely do the job if properly grounded. If you ground to the sheetmetal, then that sheetmetal better have a good ground too. If the battery is grounded to the engine, and the engine has a good ground to the frame, then ground to the frame, engine, or battery.
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Old 03-23-2012, 08:01 PM
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You should have a 10 gauge wire from the neg battery post to the fender, if you don't then you might think about putting one in...... once that's done you can use a common ground point on the radiator support....... just make sure you have good bare metal to bare metal connections, I like to use star washers, others don't but I like them. after you have good connections you can paint over the connection to prevent rust etc....
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Old 07-16-2012, 09:42 PM
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I redid the fan ground and a curious thing happened -- the fan started blowing the 25 amp fuse. The fan had worked for years with this fuse. Got to thinking about it and figured out with the better ground the fan circuit had less resistance and therefore flowed more current -- and also ran faster. So, it makes sense. Went to a 30 amp fuse and all is well.

John
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Old 07-16-2012, 11:53 PM
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I would suggest the "common ground" should be the engine block. The best reason I can give, the largest current goes to the starter. And you also need the 10 Gauge wire to the fender well.

I would consider a 14 gauge wire good for a 15 amp circuit. running 25 or 30 amps through a 14 gauge wire will cause it to heat up, even with the best connections. If a connection on the wire is a little sketchy, it will cause additional heating at the connection. with the 14 gauge wire already running hot, there is no where for the heat to go, and the connection gets too hot.
Is it a 1/4 inch spade connection? That is not really a big enough connection to not get hot with the fan current. They do make 3/8 spade connections.
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Old 07-17-2012, 09:58 AM
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The 25-30 amp current is a spike on startup. I think the steady state current is about 18 amps based on a conversation with the manufacturer.

The 14 gauge wire to the fan is the original power wire running into the fan motor. I don't think I can change the wire, although I could cut the wire near the motor and splice a larger wire onto it, but don't think that would make much difference since current still has to flow through the short 14 gauge "choke" point.

The battery is trunk mounted and grounded to a frame rail near the transmission, burnished, start washer, and sealed. From that ground point, I have a 4 gauge wire to the engine block and the new 10 gauge wire to the fender well grounding stud.

The alternator is only grounded through the mounting bolts to the engine block.

John
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Old 07-17-2012, 11:01 AM
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This is where some controversy is going to happen.
The 14 gauge power wire originally attached to the fan motor is fine, but if you have to extend it, go a larger gauge. Do not cut an excessive amount of the original wire off to make a good connection, but cut enough off so you get to good clean copper when you remove the insulation for the connection.
I like to use a crimp butt connector, that I take apart, and crimp the bare metal connector on to both wires, and then with a minimum of solder, solder the wires to the connector. Then use heat shrink tubing over the connection, or in some cases, you can use the sleeve you pushed the metal part of the connector out of. Do not use so much solder that it wicks away from the connector up the wire. It makes the wire brittle, and prone to breaking after years of vibration.

Check the voltage drop from the negative battery terminal to the frame of the starter. That will tell you if the ground wiring is adequate. Here is how to check the voltage drop.
Voltage Drop Testing

I would also check the voltage drop from the negative battery terminal to the frame of the alternator, when the alternator is putting out a heavy charging load.

I will get some disagreement on this, but I do not think depending on the mounting bolts to ground the alternator is really a good choice. The alternator and the battery work with each other to regulate the voltage in your car. The better they are electrically connected, the better they can regulate the voltage. I would suggest a dedicated ground wire from the frame of the alternator to the negative battery post, of a heavy enough gauge to carry the full charging current of the alternator, with a minimum voltage loss.

I know the metal frame of the alternator is connected to metal bolts, connected to metal alternator brackets, connected to cylinder heads, or block, with more bolts, connected to all the stuff you did to remote mount the battery, but that is a lot of connections to get loose, go bad, and possibly get some corrosion, if they ever get water splashed, or condensed on them.
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