Looking for ignition wire to splice into

[Hitchhikingmike]

I'm looking for the ignition wire in my '02 XLS four door to splice into.

I will be using the ignition wire to turn on the relay for the electric fan I am installing.

It is consecutively 95 degrees here and the A/C is always running on full blast from engine start-up to start-down. Thus I really have no reason to install a fan controller at the moment, as the fan would never turn off. So I am just going to connect the e-fan relay to some hot wire when the ignition is in run. I'll think about getting a controller once summer passes...

What wire is the best to splice into under the hood that become hot when the key ignition is in run mode?

Thanks.

 

[Hitchhikingmike]

Also, I'm looking for some good 40amp or more relays for my fan. I can't seem to find any locally. Does anybody recommend a particular brand or website to order them from other than the obscure ebay seller?

Nether autozone, pep-boys, o'relieys or NAPA carry any relays larger then 30/35 amps.

 

[BigRondo]

Did you check Radio Shack? They have a 40A SPST 12V Relay. I'll check my Haynes Manual for the diagram and post what I find. Maybe someone will chime in first with the diagram.

 

[BigRondo]

Here is the Starting/Charging System Diagram scanned from my Haynes Manual:

I can email you the full size image if you want. It's a lot easier to read. Just PM me your email and I'll send it!!

 

[Hitchhikingmike]

Thanks a lot big rondo. Just got back from radioshack. I picked up a few items for the wiring. The guy working there was surprised himself to discover that the store carried 40amp relays.

I got the 40amp relay. Do you or anyone ellse have any recommendations for fuses? I picked up some fast-acting 40amp 32vlt automotive type fuses with a fuse holder that has 10 gauge running in and out of it, but it says to use no larger than 30amp fuses. Think I will be alright with the 40amp in the 30amp rated 10gau fuse holder? After all I'm using 10 gauge wiring for the fan right now.

I read on another form to use a "link fuse", because they can sustain amp jumps of up to 30amp higher than what they are rated for for a second without blowing immediately. I have read that these fans can spike up to 75amps on startup just for a millisecond.

I'm wanting to stick at 40amp because last time the fan burnt up my 35amp relay (this relay was just connected to a dash switch at the time).

 

[Hitchhikingmike]

So for the wiring, I want the fan to come on in run mode. So does this mean I have to tap the lead to the fuse #21 at the central junction box according to the diagram? I really don't like the idea of cutting the factory wiring just for a lead. My thought is just to take the fuse out, and place the wire for the relay in the socket and place the fuse back in to hold the wire in place between the fuse and socket.

Think this is a bad idea? Thanks for the diagram, I left my haynes manual at my parent's house. (I'm at the dormitory right now.)

 

[imp]

Undoubtedly there will be a high-current surge for very short time interval upon start-up of the fan. The normal draw running must be in the vicinity of 30 amps, maybe a little less, if they recommend a 40-amp sevice fuse. If normal current draw is not more than 30, I would not worry about the #10 wire for two reasons: the "run" of wire is short, and 30-amps is usually the max. current recommended if handled by #10 wire....typically automotive wiring is "pushed" beyond usual current limits by design, because of the short runs involved. Nowadays, very high-temperature resistant insulation is used pretty much across the board.

Assurance that your fuse will handle the start-up current surge requires use of a "slow-blow" or time-delay type fuse, designed for just that purpose. Depending on type, they may typically handle 200% or more overload for 1 second or more, but open more quickly than that if severely overloaded by a short circuit. Am I helping any? imp

 

[waskly]

use a relay switched power to power the fan.

so the field power/ground will be through fords wires, the fan power will run through the relay.

 

[BigRondo]

^^^^^^ what imp said!!

 

[Hitchhikingmike]

I actually decided to go out and purchase the hyden3647 thermostatic fan control unit. I just thought I should just do it all while I'm messing with it. Only problem is that the control unit has a 25amp fuse in it. I'm thinking I will not wire the control unit directly to the fan, but to the radioshack 40A relay which will have a 40amp fuse on it.

I will post pictures and probably do a write up once I am done.

One last question: Do I need a diode? I'm assuming that the hyden control unit probably has a diode built into it. But since it will not be directly powering the fan, but another realy, do I need to install an external diode to the fan power wire?

I really know nothing about diodes other than they only allow the electrons to flow one way.

Thanks.

 

[imp]

One last question: Do I need a diode?
I really know nothing about diodes other than they only allow the electrons to flow one way.

Thanks.

The purpose of the diode is to prevent possible damage to sensitive electronics (i.e., your computer). When a running D.C. motor (the fan) shuts off, the decaying current which was being drawn by the motor can cause a big "inductive kick", which can travel back through the vehicle's wiring, possibly doing some real damage.

Best possible place for the diode location is right where the ungrounded conductor feeds into the fan motor, thereby assuring that some splice does not exist between the diode and fan, which could carry the "kick" back into the wiring.

Yes, you are correct, diodes allow current flow in one direction only; the inductive kick generated by turning off a motor always has opposite polarity, and flows back away from the motor. imp

 

[Hitchhikingmike]

So is this the place to put the diode according to this schematic?

I got that schematic from FordMuscleMagazine