To reflect the immediate effects of global warming here in Texas, I recently "upgraded" my 1995 V12 XJS cooling system with a "Wizard Cooling" aluminum radiator and twin electrical fan assembly (part #577-113MD). The effect was immediate and changed my summertime driving experience in one of joy and no longer requiring lengthy "hood/bonnet" roadside stops. The Wizard kit includes a thermal cutoff relay switch to regulate the fan on/off sequence. The original Jaguar system apparently included a connection to the electric fan that automatically switched the fan on when the AC was engaged so as to draw air across the condenser coil. This necessitated adding a relay to detect the AC compressor being turned on and provide power to the Wizard electric fans. Power to both relays comes from a "hot" feed in the engine compartment which is fine however, this feed stays hot or energized when the ignition is turned off allowing the battery to drain over a period of time. Ideally, the power feed to both relays would originate from a terminal somewhere where power is disconnected when the ignition is turned to the fully off position. Can any Forum Member identify either an accesible terminal or the ignition switch connection which is disconnected to power when the ignition is turned off?

 

I just did this installation and I'll show you what I did. Not promising that this is the best way, but it works. On the left side of the engine bay, about halfway back there is a blue relay. This is for the original small electric fan. There's a wire that goes from it to the fan that gets power when the ignition is switched on. I used that wire.

Here's the relay:


Here are the wires. You want the solid green one, not the green/brown one. Having said that, this worked on an '87, not idea if the facelift cars have the same wiring.

 

That is actually a diode pack Gareth, but I suspect you are right and it is not the same on the facelifts. Either way it works for you! But if Chris does not have this item, then this is what I did:

Chris,
On my car I also use an always hot feed from the firewall post to power the fan relay, as you are; but I used a separate ignition-activated feed to trigger the relays. There is a positive, ignition-keyed feed to the coil, so I used this, taking a feed off the coil connector. In my case, following Grant' advice, I installed a second fuse protected relay triggered by the ignition coil positive feed, to trigger the fan relay and feed 12 volts to the ignition coil. So I wired it like this:
Fan and ignition trigger relay circuit:

1. disconnect coil positive feed
2. run this to the relay trigger circuit - other side to earth (ground)
3. take the always hot feed from the firewall, run this to the power input side of the relay
4. take the power output side of the relay and run this to (a) the ignition coil positive and (b) the fan relay trigger input - replcing the permanent trigger feed.

Fuse protected relay:

This also ensures that the coil gets a full 12 volts and takes that coil-feed load off the ignition key. I used a 15 amp fuse in the relay.

 

Gareth..thanks for your reply however, as you will note from Greg's response, my XJS ahs a different configuration which is addressed by Greg. Thanks anyway. I appreciate a Members's response!
Chris

 

Greg..As always you seemed to have "hit the nail on the head" so to speak. I've forwarded your recommendation to my mechanic (the guy did the original fan and relay install but gave up on trying to locate an ignition "de-energized circuit"). Your suggestion makes sense and, assuming he can locate and hook into the fan relay trigger circuit. I'll get back to you when he replies. Thanks again (I seem to remember you responding to another XJS issue some time back). Pleased to see you there to watch over us "newbies"!
Chris

 

If the mechanic needs a diagram, just let me know and I will draw one (badly, but understandable).

 

Greg..thanks for the offer. I'm still waiting for a chat with my mechanic. I'll see what he needs and get back to you. much appreciated.
Chris

 

i was having problems with battery drain over say 1 month period, slow to no start!
so i put a heavy duty battery disconnect in the trunk next to battery , now i can leave for months 3 or more and engine starts right up!
yes maybe not for everyone but works for me!
seems when yrs of mods , there is always some micro drain, that is more annoying than pop the trunk when joy riding!
and showing off the tank and fuel system!

 

Ron..pleased to note that you still own that magnificent XJS! I have the same cut-off switch but I'm still going ahead with Greg's suggested mod.

 

Greg...just talked with "my mechanic"(sounds so pompous but the only chap I have found that cares to work on my XJS and based on what he charges, Gucci work boots, Georgio Armani overalls, etc. he knows it!!). He tells me that from your description, he can make the connection without the need for a diagram so I'm going ahead and will get back to you when completed. Thanks again for your suggestion, much appreciated.
chris