Ok, I wired up a completely new circuit today. It was as follows:

10 gauge TXL wire from the battery + terminal to the Relay Power in (relay used 1/4" terminals and was rated to 40amps)
10 gauge TXL wire from the Relay Power out to an ATO/ATC fuse (1/4" terminals)
Factory wire (appears to be 12 gauge) from the fuse to the fans using the factory connector
Factory wire (appears to be 12 gauge) from the factory fan connector to the ground post on the battery
18 gauge TXL wire from the battery + terminal to a Contura SPST switch (rated 20 amps, 1/4" terminals)
18 gauge TXL wire from the switch to the relay (trigger)
18 gauge TXL wire from the relay (ground) to the negative post on the battery

First test was a 30 amp fuse, and it worked flawlessly. I kept the fan on for about 2 minutes switching it on and off several times. It worked good.

Second test was a 25 amp fuse and it popped as soon as I hit the switch

Third test was the 30 amp fuse, but I went ahead and let the fan run for about 7-8 minutes to see how hot everything would get. Fuse never blew. Wire was slightly warm to the touch, fan motor was blazing, relay was fairly warm as was the fuse holder.

I'm pretty sure that the fans will never run that long at one time so I feel pretty confortable with this set up.

The thing that bugs me is that I made a partially incorrect statement in my last post (aside from this ohm's law bullshit). I said that the factory fan harness does not use metri-pack 280 terminals. While the fuse is a large terminal J-type fuse (40 amp), to my suprise the factory relays DO use the tiny 2.8mm metri-pack 280 style terminals. While I'm no electrical engineer by any means (as pointed out by bud), I was thinking that these rather small terminals created some resistance increasing the current draw in the circuit. If this was the case, I doubt GM engineers would have done this so I'm at a loss as to why my first trial harness kept popping the 30 amp mini-fuses. That first harness popped 4 different 30 amp fuses so that rules out a faulty fuse. I used the exact same wiring so that rules that out. These trucks exclusively use mini-fuses throughout so that must mean that they are not junk, so that is ruled out. So if someone can explain what was going on with the first harness they are smarter than me cause I can't figure it out. I can only say that I won't be using 2.8mm terminals on my real harness.

FYI, I mean no disrespect to Bud in my comments above. Just trying to be funny and lighten the mood. I admit that I am a newb when it comes to wires. I'm just trying to learn like everyone else.

 

What sort of multimeters do you have around? If you have one with an ammeter function that is rated high enough, go ahead and wire it in series with the circuit that you think is drawing the excess current. Switch on the fan and watch for the spike in current draw as the fan begins to turn on. If your fuses are below this number, they are likely to blow.
As said before, higher resistance in those connectors will decrease current in the circuit, albeit by a very small amount. Current in series is constant, so whatever current the fans draw WILL make its way through that connector. If its too small, the fuse won't blow...but it will certainly let you know its too small by melting the connector.
Not to say you don't know how to wire anything up, but it could have just been a mistake. Once you stare at the hard stuff for a while sometimes the simple stuff eludes you lol.

 

No disrespect taken brother, we're all hear to help each other...sorry if my statements came across harsh or disrespectful myself, sometimes I get a little over-cautious and over-concerning or whatever...as I mentioned earlier, been in the business a long time and have seen a lot of crazy stuff happen. Don't always know how far the abilities of all of our members stretch and I'd hate to see anybody have to waste their dough on smoked components or worse. It's all good

 

Awesome! So do you have an opinion on the two test I did?

As I stated before, the wiring was correct on the first circuit.

 

Cool deal...I would take Smokeshow's advice and hook an ammeter in series and see how many amps the fans are drawing, and check each fan separately to rule out a faulty/shorted fan motor.

 

Just a tip for you guys, building your own harnesses.

Motorcycle junkyard.


70's thru early 90's have full metal body, oring sealed relays for the Starter.
Aka starter solinoids....
They can be found in all shapes and sizes and I can promise you that your lil 25amp draw Efan will not even begine to hurt a starter solinoid.
After learning my lesson over 10 years ago. building Efan harnesses for my trucks. I switched over to solinoids from cycles and have never looked back.
Heck, to be honest. I have never had to replace one either. As far as I know, the first solinoid I installed on my truck is still going strong.

 

What is the purpose of running the fans off of the a/c compressor, or even letting the computer decide and having to get that programmed? Maybe it's a simple answer I'm missing. This all seems over complicated. My plan is to run two 14" fans, independent controller with temperature probe and power the controller from the distro block or battery. No a/c, no pcm, just fuses, relays and the already mentioned items. Thoughts?

 

Cause the PCM has the capability to control the fans with the settings you enter. It uses the Coolant temp sensor readings.
Same thing your gonna be doin with the Temp Probes where ever you place them, whether it be the Radiator or Cyl Head.

 

Yeah, no need to re-invent the wheel when hooking it to the PCM will do the same thing. You're just making more work for yourself for the same outcome.

 

I'm not sure mouting a control and sticking a probe in is exactly re-inventing the wheel. Seems just as simple as hooking to PCM, without having to worry about programming. I prefer driveway projects and staying away from electronics when possible. Doing it this way would have me investing only about $140 for a setup I've used before that I know works. My brother did it on my old 04 and it cooled better than his flex-a-lites. He's out of the country now though, so not around to help. My only question now is whether to run one fan off of the controller and the other from the compressor.