Hello! My first post on the site, I'm glad to find an XJ-S forum that seems to be visited frequently.

The short explanation of my problem is this: Back in 89, my parents bought an XJ-S new. They sold it six years ago to a guy not far from us. A month ago I found the car on Craigslist, went and saw it, and bought it back. The guy hasn't done anything to it since he bought it, which means it still has the same problem it had when we sold the car- the harness going through the middle of the V shorted out and made it so that the car won't start. (I was driving it at the time. It actually caught fire on me, the harness got so hot it melted and subsequently ignited the electrical tape it was wrapped in- a problem unto itself.)

I have purchased new connectors to re-do the harness, the problem is that some of the wires are cracked so badly that I'm having a hard time identifying which wires go to which connectors. Specifically, the two four-pin connectors at the center of the engine. I'm still not familiar with the engine bay so I'm not sure what components they go to, I can provide pictures if necessary.

I'd like to rebuild the harness (or at least refresh it) with new wire from the cabin all the way to the forward connectors at the front of the engine bay. As mentioned previously I have new connectors ready to go (bought a couple C5 corvette alternator plugs and ford injector plugs that will do the trick) but need help with a wiring diagram so that I send these wires to the right place.

I've done some searching (Captain Jaguar's website doesn't appear to be working) and couldn't find anything. Can anyone help me out? It's a 1989 V12.

Thanks in advance!

 

http://www.jagrepair.com/images/Elec...Electrical.pdf

 

I can tell you from first hand experience, that this is doable....However, keep in mind, that if you have a Marelli 89, there is coax in the ignition harness. And it needs it. I am more than happy to discuss with you if you need a moral booster. PM me your number if you need to talk about it.

 

Thanks for the info! A morale booster to get me started would be great; I'm not new to auto repair (if my Olds Aurora does one thing well, it's give me problems to fix!) but I am new to Jags. I do have a couple questions, any advice you could provide would be much appreciated. Thanks! PM sent.

 

So I can't figure out where PMs are. My Aurora forum runs on ProBoards software, I'm still unfamiliar with this setup. superchargedtr6, could you shoot me an email to xjsman89@auroraclubna.com so that I can send you my number that way?

Thanks!

 

No problem! Just sent you a email.

 

At the right top of the page is a box that says Welcome (your name), under this is the line, Private messages : unread X total X. Click on the unread ......

 

Malc4d, It turns out I don't have access to PMs yet as a junior member. I read the "Read this if you're new" post and discovered that. I guess that's what the post is there for. haha

Thanks for the call, Gene! It was great getting some first-hand information. From the wiring diagram provided and a couple other ones that I saw I think I have a decent handle on it now. Do you (or anyone else) have any idea which wires specifically are coax? Is it just the two magnetos on the bottom of the motor, the crank sensor and the tach sensor on the flywheel?

The only wires that I believe I need to replace are the ones going forward to the amps, Going back to the A and B coils, one sensor in the V, and two on the passenger side at the front of the motor. I think I may not have to replace any coax wire. In taking my harness apart I haven't found any cable that looks to be coax, it's all normal stranded wire so far.

As always thanks in advance, gents!

 

The 89 coax wires are the front and rear magnetos (sensors), and the wire going to the Lucas ECU. Somewhere along the end of the 89, start of the 90 model, the feeds going to the amps were also coax. So figuring there had to be some sort of feedback causing misfires(?), I used 5 coax leads in my harness. If you look at the schematic, close to the ECU, you will see a wire indicated coming from the ECU, and then have another wire leading to a circle around that wire. The schematic calls this shielded.

 

Got it! I actually cut the harness where it goes to the amps (because it was all melted in the middle anyway) and got a good look at all of the wires. All of them are normal wire, no double-stranded stuff from what I can see. So it looks like the car is an earlier 89 model with no coax going to the amps.

I'm sure once I get into the harness I will find them, just wanted a better idea going into it. Thanks!

 

So I have progressed only a little bit (garage isn't heated, so it's hard to work out there sometimes) but I believe I have identified a coax wire.



Is this what I'm looking for? This is the only coax wire that I have in the wires that were effected in the fire/short. It was coming down the feed in the main valley, but I don't see it going forward to the amps. (had to cut those wires too, so I can see inside those and all looks normal.)

So it appears that I have an earlier 89 with only the 3 coax wires? I still don't know where it goes, it disappears into the wrappings of the old harness and I have yet to cut it open to see where exactly it goes to. I'm guessing the Lucas ECU.

Any insight you can lend to me would be helpful! Any idea where to go buy the correct coax wire for this?

Thanks!

 

The only three coax that I am aware of on the early 89 go to the speed sensors, and the Lucas EFI unit. The wiring harness ahows them as "shielded". As I said, when I built mine, I used coax to the amps, only becuase of the change on the 1990 harness. Figured Jaguar, Marelli, or Lucas had to have had a reason for that.

As far as the automotive coax, I got mine from a place called Harleys Electronics in Spartanburg SC. They sold it by the foot. Good luck with your project, and keep us posted!

 

I worked on the car a bit this weekend. I took a good, hard look at the diagrams on the last two pages of the PDF that malc 4d provided and they are exactly what I need. I made myself a "cheat sheet" if you will for my specific situation detailing where all the wires go. The plan is to start soldering tonight.

I bought some copper grounding braid off of McMaster Carr that I'm going to chase my normal 14ga wire through and use in place of the coax wires. As long as it's grounded it will work the same, and it was cheaper than buying Mil-spec single-wire shielded cable from aircraft spruce and the like. I only have two coax wires that were affected by my short/fire. The crank sensor at the front and the EFI wire at the rear. I haven't seen the flywheel sensor wire at all.

I'm hoping that it will go quickly, the setup is always the hardest part. I have some oil to put in there too, It surely will need an oil change after sitting for 6 years. I should probably get some fuel stabilizer and better gas, too.

I'll keep everyone updated. Hopefully she'll be running by this weekend, Lord willing!

 

To be safe, it would be a very good plan to also renew the injector loom. This is bound to be old and cracked, and if it grounds, keeps the injectors open 100% of the time and burns out the cats, etc etc disaster! It could also be part of your original trouble. This is really important, I believe. Welcome and good luck. Greg

 

I sincerely hope you are making a good choice. When I bought my car, it had a harness that had been built by a "professional" wiring company. They did not use coax. It would not work. They had used shielded twisted pair. I am not a electrical guy. But the coax seems to have something to do with hertz(?). The signals become frayed once those small magnetos start producing AC voltage in higher frequencies. (I think). I will say again, I only paid about 29.00 for my coax from a place in Spartanburg SC called Harleys Electronics. They had a spool of it. Guy talked like they didn't sell a lot of it. I bought enough to convert my harness to be like the 90, which had coax going to the amps as well as the "sensors".

I used the wiring diagram, and did each run independantly from the ECU to the point of contact (ie amp, sensors, etc.).

 

Did they use external shielding for their wire? I believe the point of coax is to ground the outer ring to provide a shield from the noise of other wires in the loom and/or to keep the signal in the wire on the inside from getting fragmented. With an external copper shield, it should accomplish the same thing as long as it is grounded. I found that one of my wires (the flywheel wire, specifically) was shielded in this manner, and the car was running fine up until the short.

Thoughts?

 

Yes, they did use a outer shield. But it didn't work. The issue was discussed at length on another forum as well, and from what I understand, a coax seems to protect its own signal. It must act like a radio wave around itself. When it gets up in a high frequency, its signal becomes scattered on a twisted pair, even with shielding.
I actually purchased a handheld oscilloscope to see the sine wave the "sensors" put off, to see if they looked like those in the ROM manual. The truth is, I still have no idea what I was looking at, just that my "sensors" weren't putting off the signal the manual said it should. So, I felt I HAD to search out coax vs shielded wire. Seems there is a big difference.

 

I called up Harley's and it seems they don't have what you purchased any longer. The only shielded single conductor wire they have is a 14ga foil shielded outer with a solid 24ga inner wire. When I mentioned "automotive coax" he did say that it's just shielded wire, though, so either it's just really uncommon or they're one in the same? I wish I could find a definitive link for "automotive coax" somewhere to be sure that I'm getting the right thing, but all I can find is shielded wire stuff. If it's just stranded wire inner and outer I would think it's just shielded wire... it's not like a different kind of metal would shield it better than another, right? As long as they're both stranded and the right gauge it should work the same, I would think.

 

Here is the disclaimer I am not an expert on Marrelli ignition car's I am however looking at one so that could change.
I think going to an aircraft coax may be prudent for this application from experience I know there are a lot of options in size and electrical properties.

 

I'm old enough to realize how dumb I am. I don't understand the why's of what I about to write, but tokyodon may have the answer. The wire I bought from Harleys was a very small coax wire. It was about 24-26ga stranded center.

The coax has something to do with hertz. The "sensors" put off some sort of high frequency that can disrupt the signal on surrounding wires somehow.

I am a builder. I don't know why, but we cannot (or aren't supposed to) put low voltage, and high voltage wires in the same pathway/box.

Again, not sure what goes on with the hertz, but there is a guy on another forum, that is a electrical engineer, and as best he could in laymans terms, explained what was going on. All I know, is that someone built a harness for my car prior to me buying it. It had shielded twisted pair, and it simply would not run. The wire I bought from Harley literally looked just like a TV cable wire, only small. Like 1/8" diameter small. I am going to be near there tomorrow, and will see if I can stop by, and confirm for you what I know worked on my car.