Hello all,

I have a beautiful 74 XJ12L RHD that was mechanically restored about 1500 miles ago. New wiring, ignition, starter, suspension, top end of the engine, etc. Recently I've been battling an issue with the car needing to be jumped almost every time I go to start it. At first it was after it sat for a few days, now I have to jump it every time I go to start it.

I replaced the battery a few months ago. Car easily takes a jump with a lithium jump pack...volt meter shows solid charging when the car is being driven. All lights, windows, wipers, etc work fine, no flicker or obvious signs of weak power. Both battery terminals are basically new, clean, and well connected as they should be.

First question, there is one small wire that runs along the firewall right under the lip of the bonnet frame, that connects to the chassis on the firewall. It looks fairly old and maybe burnt a bit at some point, but when I follow that wire back to it's source, it's coupled with a brown, red and green wire that appears to go to nowhere. The ends of that little wiring harness are the white insert connector types, laying next to the battery, and don't have anything connected to them. I'm guessing when the previous owner restored the car and the wiring, those were disconnected for some reason because of all of the upgraded ignition and electrical parts he installed.

However, a couple of times when I've been jumping the car, and really having to crank it for awhile to get it to start, I smell burning rubber/wire and see a tiny bit of smoke coming from around the battery wires, and possibly that burnt looking wire connected to the firewall, even though it appears it's not connected to anything at the other end.

Alternator and all other engine and electrical components have less than 1500 miles on them since the restoration. The new battery will still charge overnight with a charger and will start the car maybe 2 times. And it's not the trunk light, that's been disconnected. No interior light issues, no mods or upgraded radio, etc. I'm at my wits end trying to figure this out. Any suggestions?

 

Just to clarify, it is attached to the firewall as you'd see with a ground/earth wire?

The battery cables are overheating, most likely. Possibly, if they've been replaced, they're undersized and can't handle the load. or perhaps the starter is drawing excessive current. This might not have anything to do with your battery drain-down problem

Many videos on how to check for parasitic draws. Here's but one example


Cheers
DD

 

Hi Doug, thanks for the reply. Yes, the wire I'm talking about appears to be a ground wire of some sort bolted directly to the firewall, with the end of it being the little "eye" hook type. The end of it was pretty burnt and rough looking, so I stripped that and just bolted the cleaned up wire directly to the same bolt. Again, it doesn't make sense though, because the 3 wire grouping that this wire is connected to doesn't appear to be connected to anything at the other end.

You might be on to something with the battery cables being undersized and overheating. The car does have the upgraded reduction gear starter. I'm sure that takes more juice to get it going.

There have been a few times when I was jumping it, where I would only get a slight click of the starter, or sometimes, nothing at all. I then go to that wire that's bolted to the firewall and wiggle it a little bit, and wiggle other wires down the line, and eventually it will jump. But no matter how long I drive it, when I go to start it the next time, it barely turns over, if at all. Hope this helps. I'll check out that video.

 

I would remove the small wire that is grounded at the firewall and has no clear connection at the other end and see if anything stops working. I don’t think the original wiring had any 3-colour wires, should be one main colour and one tracer colour for this era of cars. This wire could well be a source of current drain especially if there is evidence of scorching

 

A week's pay say you simply have a dirty or loose connection somewhere. This shouldn't be too difficult to rectify...although the connections at the starter itself might be difficult to reach.

Couldn't hurt to have the battery tested, even if it is only a few months old

Cheers
DD

 

Agree. Remove that mystery wire. Not the source, but useless.

Hot cbles mean high resistance.

The GR starter may use less volts than the original unit.

Report on the use of the bulb in series at the battery as in the video.

Good grounds. Clean all cables at each end. fixes lttsa stuff. Been there, done that.

Carl

 

If you drive a few miles, then stop and try to restart, does the starter turn the engine? If not, I'd check the connections to the battery terminals. If they are OK, is the alternator charging the battery?

 

the alternator may not be charging.
the reduction gear Starter may have been wired incorectly.

check all the exterior and interior lights at night, is any light staying ON?

open the boot slightly at night, check to see if the boot light stays ON. Then open it and check the on/off switch at one of the Hinges to see it it turns OFF the boot light.

has the Radio been wired recently? maybe the Memory wire was inverted with the Power wire?

and yes, check the Battery to see if it is holding the charge.

 

Thanks to all of you for the replies and suggestions. I'm hoping to get to work on it this weekend or early next week. I'll let you all know how it goes.

 

With the car idling can you put a volt meter right on the battery posts them selves and see what the voltage is? Should be around 14V, maybe 14.5. That's a test to see if the battery is charging and if the connections to the battery are ok.

 

I finally figured this out, with all of your help. Many thanks.

I figured out that the extra wire going to the positive chassis mount (a double bolted screw going directly into the firewall steel) was a positive lead for the BATTERY FAN! The unconnected wires at the other end were for the battery fan connection. I had taken the fan off when I bought a newer battery that was a little too big for the fan casing. Keep in mind, this is a 74 XJ12L RHD, and I've learned over the years of owning these cars that the battery fan can be quite essential on some cars.

The issue with the short/non charging of the battery turned out to be the chassis bolt itself. The positive battery cable is bolted on the first "half" of the bolt that goes into the chassis, There's a washer between the first and 2nd nut on that bolt, which is where the circular end of the battery cable mounts, and as it turns out, the wire that feeds power to the battery fan box. The problem with charging the battery apparently was the fact that the secondary nut on the bolt that goes into the firewall was both corroded, and very loose. I had to fiddle to get both the 1st and 2nd nut as tight as they would go, sprayed them with gunk cleaner stuff, and it started just fine with a freshly topped off battery.

One question to put forth to all of you...how important is that battery fan box? I've wondered over the past 2 years if I was burning up new batteries because I took that fan off, because it wouldn't fit over the batteries (3 now!) that I've put in this '74. I have a modern secondary temp gauge mounted in the glove box that gives me accurate engine temperatures. Even though this 12 cylinder was completely rebuilt less than 1000 miles ago, it constantly run at about 200 degrees F. There's never been any issues with overheating or the car acting like it's struggling, it just runs hot, like most V12 Jaguars do. Is 200 F enough to burn up a battery without the fan installed?

I'm thinking not. I'm guessing I went through 3 batteries because of the very loose and dirty connection to the firewall bolt. But could the lack of the fan box not being installed also be a part of the issue?

 

the battery fan used to be important until the Series 3, when it looks like it was deleted, at least in cars exported to USA, I've never seen one fitted.

 

Well...interesting past couple of hours...after cleaning and tightening the connections to the firewall bolt from the positive battery cable, my wife and I started it and let it run for a bit. Then, major smoke from the positive battery cable. It got so hot it literally melted the ring off the end of the cable, and about the first 3 inches up the cable! WTF???

The only thing I can think of is the spray can I used to clean the bolt with...I didn't have any WD40 or anything like that handy, so I used a basic degreaser/conductor type of stuff. It must have caught fire ones it got hot. I still can't believe it actually burned the O ring off the end of the positive battery terminal. Going to the parts store now to get a new one. I'll reconnect everything without any spray and hopefully that's the end of it. If not, there is a serious power/ground issue going on here. Grrrrrr!

 

It could be that the positive terminal post has a short or partial short. Perhaps the insulator between the bulkhead mount and the terminal itself is breaking down

These are part number C45021 and are available from SNGB and others. https://www.sngbarratt.com/English/#...20%60C45021%60

 

Sure appreciate that link, and yes, at this point I'm wondering if it's exactly as you say. My wife and I just drove it for an hour after installing a new positive battery terminal cable. Voltage meter never got above halfway the whole time, usually it's around 1 or 2 o'clock, meaning charging at 13+ volts...sputtered and backfired when taking off from a traffic light, etc. Something is definitely still wrong. It's not charging correctly and it's not supplying the upgraded ignition with enough juice to run correctly. I'm going to make one more attempt at tracking this down, and if I can't, it's going to go to a very reputable (and expensive) specialty shop here in the Dayton, Ohio area. Everything else on this car is just perfect...I've got to get this fixed. I'm sure it's a simple issue but I'm getting frustrated.

 

This issue definitely appears to be solved.

I finally just removed the wire for the battery cooler box from the bolt going into the chassis, the one that the positive terminal connects to from the battery. Brand new positive terminal, and yes, I did take my 6 month old Duralast battery back to Autozone, and it was charging slow, so they gave me a new one.

The main thing that I think fixed this, is with everything finally off of that bolt that goes into the chassis, I was able really get that bolt and whatever it's attached to on the inside side of the firewall very tight. I had to use a wrench and vice grips to keep the bolt itself from turning (and not damaging the threads on the bolt!), to get that first screw tight up against the firewall plate. It was definitely not tight enough before, even with cranking it and the nut on the other side of the bolt that holds the terminal on the bolt.

The car now charges correctly, starts easily over and over again, no sputtering or idle issues, and in fact is more responsive and just "better" in every way now while driving it hard.

The question is...with this solution hold? I hope so! Thanks to ALL of you for your help.

Nick

 

 

Been there Done almost that. but, at the starter. In my starter nightmare, i swaped in several. guess i did nt get one tight enough. Cooked the end clean off juast volts juming the gap. new and better cable properly istalled. fixed.

Oh, anther one. side post batteries nt my favoriteds. i failed to tighten the little bolt. Lose cable. voltsjumpped the gap. melted the solderedin connector in the battery. Tried a couple of bodges, Not good enough good by bttery, got a new one. solved. Lessonm. Clean nd tight connections.

 

Beautiful Jag, Skepcat! And yes, I'm biased.

Did you add that wonderful "Euro" bumper & lower grill, or did you find it that way?

Makes a huge difference in the Series II 'face'.

Next time you disassemble/reassemble any bolted ground, use copper neversieze. Keep doing all the other cleaning steps, just add copper neversieze.

 

Skepcat67,

Didn't notice steering wheel emerging from glove box.

Your car was born with that face!