question about nelsons wiring harness.

[TXsilverado]

two questions actually.

how do i go about wiring in a switch to turn both fans on 100% when i want....

also. when i had my vsc wiring harness the vsc somehow did a soft turn on so it didnt give my alt that innitial jolt of power loss. is there some kind of doom-a-hickey that i can splice into the harness to slow down the current when the fans kick up so my lights wont flicker anymore. that was the only thing i liked about the vsc.

[SlammaDingdong]

Hey Tx, the doom-a-hickey you're talking about is an automatic potentiometer (kind of a "fast" automatic VSC). It's sort of like a rheostat, except for providing variable voltage based on a reference voltage. They are commonly used in lots of applications for ramping up voltage, but i'm not sure about finding one that would be "automotive grade".

For doing the on demand 100% fan speed using the Nelson harness, you'll need two automotive grade relays and a diode (plus your switch). The trick is to apply a current to both the PCM and A/C trigger wires. You need two relays since the PCM trigger and the A/C trigger are opposite polarity. The diode is used to keep the A/C trigger from feeding back and activating the compressor clutch. You could actually get by w/ one relay, but i would prefer using two because it's consistent and isolates both trigger signals.

You can get the the relays and diode at good old Radio Shack. A pack of diodes will be about $3 and the relays about $7 each. From the diode pack use the one marked 1N4007. It will handle a 1A load, which is more than enough for this application. You'll have to solder a couple of wire leads on the diode for splicing it into the harness, and then figure out how to protect it. For a cleaner approach, you can use a "Mechanic's Diode" like this:

http://www.alternatorparts.com/Alter...brackets_3.htm

Here's a [somewhat crude but accurate] diagram I whipped up that shows how to wire it. Hopefully it will help some other guys too:



For the 1N4007 diode, make sure the silver band "points" towards the relay.

Hope this helps. Let me know if you have any questions. If you have trouble viewing/printing this, let me know and I'll e-mail it to you.

Jeff

[TXsilverado]

argh...i liked my factory looking nelson harness...if i try wiring that in i would have it back to looking like a vsc system with wires running everywhere looking like crap . is there a way allen could send me just the switch he makes or does it all need to come in a bundle.

thanks for the help slamma! im guessing your some kind of electrician? someone will be able to use this diagram for sure but i just dont have any skills!(You know, like nunchuck skills, bowhunting skills, computer hacking skills, or wiring skills)

[SlammaDingdong]

Originally posted by TXsilverado@Jun 28 2005, 10:33 AM
argh...i liked my factory looking nelson harness...if i try wiring that in i would have it back to looking like a vsc system with wires running everywhere looking like crap . is there a way allen could send me just the switch he makes or does it all need to come in a bundle.

thanks for the help slamma! im guessing your some kind of electrician? someone will be able to use this diagram for sure but i just dont have any skills!(You know, like nunchuck skills, bowhunting skills, computer hacking skills, or wiring skills)

LOL. No, i'm not an electrician, but maybe even worse, my background is in physics. I just try not to be a big geek about it.

Tx, don't let the diagram scare you, it's really not that bad. But that's cool, you gotta be comfortable w/ what your doing.

Now, using NO relays, with just basically a switch and a couple of wires it's really easy to make the fans run 50%. The 100% deal is just harder because your dealing w/ triggers that are opposite polarity.

I don't think Allen sells the switch deal w/ his harness anymore, but he can verify that.

Jeff

[SierraCrew]

He sells it with the wiring to connect the switch but not the actual switch. You just have to pick one up from autozone or whereever. I just got mine. Big question though, anyone have the installation instructions for the Nelson harness. Mine came without any.

[TXsilverado]

if i remember straight.... the red ones go to the junction box, the blue ones ground(on alt bracket), the one with a pin goes to the cpu(bar closest to engine on pin 42) and the other 4 go to your fans. (hope i got that right) i threw mine away, but i can help you install them if you want. i have a big garage with too many tools, or i could come your way if its not too far. i'd like to see how allen has the switch wired in....does your wiring harness have 3 relays? or are there more?

[SierraCrew]

TXSilverado,

Yeah, Allen sent me a copy of the instructions. But I do have one more ??????? How do I know which one is pin #42? Is the PCM numbered like this? I have never really paid attention to it that much, so I'm just trying to make sure I have all the info I need.

[TXsilverado]

it is numbered on the backside where you will be pushing the wire through. you cant miss it.

[SierraCrew]

Cool, Cool, thanks.