I just completed a modification to my wife’s 1990 XJ-S convertible (5.3L V12 w/ Marelli) to utilize the previously unused green “Caravan” warning light on the instrument panel as an advisory light to show when the auxiliary cooling fan is powered on. I used a double bullet connector to get the 12VDC from the auxiliary cooling fan, routed the new wire inside the engine bay rearwards to beneath the brake fluid reservoir, through the coolant catchment tank bay behind the left front wheel, and then into the interior of the car where I soldered it into the Red wire going to pin #7 of the small instrument panel connector. The attached 7 pictures show the basic idea. The pictures aren’t organized in the sequence that I uploaded them, but that probably doesn’t matter much.
We have had several instances over the past 10 years when the auxiliary cooling fan did not come on when it was supposed to. Of course this meant higher than desired coolant temperatures and worries about dropped valve seats. One time it was due to a failed cooling fan relay, another time it was due to a failed thermostat. On several occasions I never did figure out why the auxiliary cooling fan was not on when it was supposed to because the next time it worked properly.
After my recent engine bay work, including changing out the radiator and installing all new belts and hoses, I wanted to be sure everything was working properly, especially the auxiliary cooling fan. While driving the car over the past week or two the “Caravan” light was out until the coolant needle approached the middle of the “N”, and then it stayed illuminated until the needle dropped to the very bottom of the “N” and then the “Caravan” light went out. The “Caravan” light stayed illuminated after engine shutdown if the auxiliary cooling fan was on and until it shut down as expected. I never could hear the auxiliary cooling fan running while driving this car, especially with the wind noise with convertible top down. Now it is reassuring to see this advisory light illuminate and the extinguish while driving. The light staying on after shutdown as long as the auxiliary cooling fan was running gives me further confidence that the fan is working as it should. Now if this light doesn’t come on when the coolant temperature is at or above the middle of the “N”, it’s time to pull over and investigate. We get 100F temperatures on a regular basis this time of year and coolant temperature is a major concern of mine especially with other family members driving this car.
BTW, while I had the instrument panel out I took time to clean all the contacts on the connector plugs and the instrument panel flexiboard. It was a while since I did this and the somewhat intermittent speedometer is now rock solid while driving and the tachometer also appears more accurate at higher RPMs. I added an extra ground wire 10 years ago so I also cleaned up those connectors as well as the ground point.
The attached pictures provide insights into this modification.
Paul,
Thanks for sharing that information. It is something I may consider doing. I have had a relay go bad before causing the fan not to come on. I did have a fan motor fail also. Would this modification catch that failure?
Thanks. I have been thinking about doing this modification for a while, particularly after discovering the unused green advisory light and experiencing a variety of auxiliary cooling fan issues over the past 10 years. This certainly won’t prevent an auxiliary cooling fan failure, but it does make it more likely to recognize when the fan isn’t on when it should be so that you can take proper actions like pulling over and investigating.
I am in the process of making a few additional modifications to my wife’s 1990 XJ-S convertible to improve it based on some of her comments while driving the car. The first one was to remove the green lenses over the instrument panel lights and to bypass the rheostat to give full illumination of the instrument panel at night. She really likes the difference that made for her while driving this car at night. The other one was to add new “courtesy lights” in both front passenger footwells tied to the two white interior dash lights already there. I already finished the passenger side and it looks quite inviting now when stepping into the passenger seat at night with the footwell nicely lighted. I plan to install the same feature on the driver’s side soon and will post pictures and instructions when I am satisfied with the modification.
This is what the owner’s manual for my wife’s 1990 XJ-S convertible says about this “Trailer” light: This can be utilized if the vehicle is to be used for towing a trailer, and a heavy duty flasher unit is fitted. The spare red lead will be found at the rear of the instrument pack adjacent to the steering column; this should be connected to the W/L terminal of the heavy duty flasher unit, when fitted”.
I don’t see this as a “Warning Light”. As a former military pilot I am used to green “Advisory Lights” to report on the status of a system. I suspect that this light was designed just to remind the driver that a trailer was connected to the car, but I am not certain of that. For me it was an opportunity to address the auxiliary cooling fan status that I wondered about from time to time. Now it is obvious whether the fan is powered or not, especially when it can’t be heard while driving (particularly with the top down).
We don’t own a trailer or a boat, and don’t ever to expect to. So converting this green advisory light to another function made a lot of sense to me. I wish I could change the symbol on it to a fan icon, but I don’t know how to do that without messing it up. For now it looks pretty good to me and does something functional.
I thought a lot about this before making the modification. It seems that there are just a few likely failure modes of the auxiliary cooling fan, and I think this modification covers just about all of them of them. First as a reminder, this isn’t a “Warning Light” to indicate the failure of the auxiliary cooling fan, but an “Advisory Light” to allow you to monitor that the fan is going on and off as it was designed to. When working properly the advisory light will be illuminated whenever there is 12VDC to the Black-Green wire going to the fan. This happens when the coolant temperature has reached the middle of the “N” or higher, the thermostat closes and the cooling fan relay closes and provides the 12VDC to the Black-Green wire.
Here are the failure modes that I thought of (there may be more):
Thermostat fails and fan is not on when it should be.
Cooling Fan Relay fails and the fan is not on when it should be.
Auxiliary Cooling Fan fails and blows fuses #3 and/or #5.
#3 and/or #5 fuses blow not due to Auxiliary Cooling Fan failure and fan is not on when it should be.
Black-Green wires from the cooling fan relay is severed.
With any of these failures the advisory light will not be on when the coolant temperature is above the middle of the “N” or higher. So it is time to pull over and investigate.
It’s important to note that the auxiliary cooling fan isn’t on all the time, even when it’s hot out. While driving this car for the past couple of weeks it is reassuring to see that green advisory light turning on as the car is being driven and the coolant temperature rises above the middle of the “N”, and then extinguishing while driving when the coolant temperature drops to the bottom of the “N” when driving down a long hill or into cooler weather. The auxiliary cooling fan should normally be turning on and off depending on the ambient temperature and your driving conditions.
I’d say that if anyone doesn’t hear their auxiliary cooling fan turning on after the coolant temperature reaches the middle of the “N” they should investigate whether their auxiliary cooling fan is working by jumping 12VDC from the battery directly to the Black-Green wire at the cooling fan.
Beautiful work Paul !
I also have enabled my trailer light so that whenever my trailer is connected the little caravan icon illuminates reminding me just in the event that I’m not already aware that there is a trailer in tow. And it is quite pleasing to finally see that warning light illuminated after all these years.
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
9
Aaaargh! Maybe it’d be worth wiring two relays in parallel? Of course, the
problem with that is that one could fail and you’d never know it until the other
one failed.
Back in my consulting engineering days, we had a similar issue with air
conditioners for telephone switching equipment. It was critical; a failure of
the A/C could destroy lots of expensive equipment. So, obviously there were
two air conditioners, each of which could handle the entire load. But what
happens if one fails and you don’t know it has failed? We had discussions
about airflow switches and temperature switches in the ducts, and then
timers had to be added since neither the airflow nor the temp would indicate
successful running when the system first kicks on. It got more and more
complicated, but it was necessary for an A/C system to send a signal to a
remote location to get a service crew out there to check on it.
The solution for the overflow condensate drain pans was simpler. An A/C
system always has a condensate drain, usually outside. To avoid damage,
we always added a secondary pan under the entire unit. If it drained outside,
you’d never know anything was wrong with the primary drain. So one
solution was a microswitch mounted in the secondary pan with the lever
sitting on an aspirin tablet. If water got in there, it’d dissolve the tablet and
set off a warning. Or, an even better idea, somebody I knew set it up so the
secondary pan drained through a hole in the ceiling directly above the toilet
in the bathroom. Didn’t hurt anything, the condensate just went down the
toilet, but if you sat down to do your business you’d know for sure the
condensate drain wasn’t working right!
Thanks for the clarification. More than a couple of decades ago, I bought the bones of an old trailer. all I wanted were the two 35 Ford 16’ wire wheels foe my roadster project. I added to the frame and built. It served for a few year, mostly hauling yard waste.
Point. I durn well knew it was hooked up. No need for a warning light to tell me it as following me. Seems a better advice was that it had departed or off the ball and on tot he safety chain!!!
Fellow Jaguar owner, Bob Loftus, helped me with a needed warning lamp. O2 sensor lamp became “CHECK ENGINE”.
Needed to make the CA SMOG referee happy. Printed on a transparency. I managed to remove the existing and slip in the new one. It looks “factory”.
One of your fellow military pilots is probably in the “soup”.
“screwed the pooch”, I think is the saying. Acrobatics and sonic booms over Walnut creek!!! An F16 guy. So, either
Air National Guard or AF. I suspect the former…
Kirby:
In my former profession, insuring boilers was a specialty of one employer. Low water meant big trouble. The function of a “low water cut off switch” was of utmost import.
Thank you for the kind comments. I have made a several modifications/enhancements to my Jaguars over the past 17 years and consider this one of the more elegant and practical ones.
I never did find the end of the red wire going to Pin #7 of the small connector. I looked for it where the owners manual said is should be but never found it. So I cut the red wire about 4 inches from the connector and soldered in the new wire from the auxiliary fan. Did you find the end of the red wire? Or did you do what I did?
great idea well executed Paul. And as usual, photos added to the words make it all easy for dummies like me to grasp. Really like your photos and “arrowed” captions.
Thank you for the kind comments. I hoped that others on this list would find this modification helpful and implement it based on my pictures. If you do, I would appreciate feedback.
As I mentioned in another post I also modified the instrument panel lighting to brighten it up by bypassing the rheostat and removing the green lenses. My wife likes this modification a lot as she always commented about how dark the instruments were while she was driving at night. I am also adding new courtesy lights in the driver and passenger footwells to illuminate that area whenever the dash interior lights are on. I completed the passenger side and plan to finish up the driver’s side soon. I will post pictures of those modification when I complete them modifications, I am confident that they work well, and they are ready to share with other.
That’s quite a thorough and really interesting essay…my opinion is that I am not complicating any more than absolutely necessary…I just listen to the fan.
We have ac units that cool a server in the projection room of the theatre I help manage. There are two. .one sits high and drains into the regular drain. …the other into a bucket …since it is only on while projecting we just dump the bucket. …simple old fashioned methods.
Hi Paul, I never found wire either. What I did was tap into that wire for pin 7. I will take a pic next week when I’m home.
I did a lot of electrical enhancements with switches and lights etc and will have to remove my instrument cluster again to investigate why my turn signal indicators aren’t lighting up. Its not the cluster itself(as I had spare to test) so I have narrowed it down to possibly a bad diode (1 of 2) maybe both behind cluster.
I don’t think many could tow a trailer behind an xjs and forget its there. I would think the light would be to let you know the trailer lights are connected.
