Hello all,

I spent yesterday doing some jobs on the car - I'll do a full list at the bottom of the post, but I think there's only a few that are likely related. Essentially I went to bed quite happy, having completed my job list. I left the car with the battery fitted and connected, with a compensator on it - normally when I leave the car for any time I disconnect the battery terminals, but as it was only overnight I figured it would be OK.

This morning I came down, turned the ignition on and heard the fuel pump clicking - I also tested the washers (see list below) and they worked. Went to start the car, and nothing. No click or anything.

Suspected starter button broken, so tried the button on the solenoid - now got a click but no attempt to turn over.

Very confused, I turned things on/off and over the course of about 20 minutes came to the conclusion the battery was flat. Headlights didn't work, slowly the fuel pump stopped it's clicking and ignition/handbrake lights dimmed. Interestingly the interior lights functioned correctly throughout (i.e. on with the door open).

More testing - discovered that my jump leads are knackered! But fortunately I had a spare battery that fits the car (actually the original one it came with, which was misguidedly replaced and is fine). Testing across the terminals of the suspect battery showed it was only reading 9.8V. The spare battery at this point was 13.5V.

Fitted the spare battery and the car came back to life - cranked and started fine, headlights worked etc. However I was suspicious, and over time things started to deteriorate - after 20mins or so reading the voltage across the terminals showed it was only at 12.5V - I'm not sure whether this is expected just by connecting up the car electrics to the battery? I would have thought not.

Removing the battery, measuring resistance across the battery lead connectors gave me almost nothing - 35ohms. So I've got a short somewhere?

The only electrical thing I'd played with was to fix the indicator tell tales, so I first dismantled the bezel on the column again and separated the wire bundle back out. The resistance now read ~150ohms - so still not the open circuit I was hoping for! Am I correct to be looking for open circuit, or are there other bits of the electrical system that are always on (perhaps those persistent interior lights)?

A final test I did was to refit the battery at 12.5V, and try and use the indicators - I found that they worked for a few seconds, then I heard a click and then the stopped working. A cycle of ignition off, then ignition on, I heard a click as the key was turned, and then the indicators worked again for a bit. At one point the indicators just stopped working whatever I did. My original fix to the telltales involved soldering the contact on the column end of the connector for the right turn tell tale (the indicators have always worked, just not the tell tales) - one of the attached pics shows what I did (it's the lower contact). I wonder whether the heat applied with the soldering iron has done something to the flasher unit (also shown in another pic)? It's a bit of a long shot? NB there is some glue on top of the solder.

The alternative is that I've got some dodgy wiring - from what I can see the main bulk of the harness is original but looks in good condition (previous advice has been to leave it), although the extremities have obviously had some DIY done to them at some point. I've attached some pics to show the general health of the wiring under the dash and behind the central panel.

I think my next step is to measure the current draw between battery (positive terminal, positive earth) and ground - does anyone have any expected values with the ignition off? Assuming it's larger than expected, I can then start unplugging things to see if it drops and hopefully find the culprit - but I'm not sure what I do if I read a sensible value.

I have a few weeks before I can get near the car again, so would like to compile a list of sensible things to check and the best fault finding method! It's my first real foray into the electrical side of the car.

Just for reference, the battery that went flat is barely a year old, and has been on a compensator its whole life. It's possible I left the drivers door open, which would have meant the interior lights were one, but I'm surprised it dropped the battery that much, and it still doesn't explain the drop of the second battery and the weird indicator flakiness.

Your thoughts and suggestions are welcome!

The joblist I did yesterday:

refit overhauled rear calipers and bleed brakes
refit overhauled handbrake calipers and new handbrake cables
discovered the washer motor had been wired up backwards so it was sucking not blowing, and fixed!
Replaced windscreen wiper blades
Replaced bulbs in overdrive/indicator tell tales on dash bezel
Discovered RH telltale contact wasn't touching indicator stalk contact, so attempted to bend contact blade slightly - broke off blade, so cleaned it up, put a bend in it and soldered it back on.
Reassembled bezel, including moving (just out of the way, nothing unplugged) some wires under the driver dash.

B

 

I think you are on the right track. There should be nil current draw when you connected your multimeter (set to amps) when connected in series with the battery terminal & earth/ground. (Except if your electric clock happens to work- a bit of a Jaguar rarity!)

The only live circuits with the ignition switched off are the brown coded circuits e.g.ammeter, horn (via fuse) and light circuits (via light switch or courtesy lights).

If you have an alternator fitted, and if the diodes in it are faulty, the battery may cause to discharge thru the alternator. But as you have mentioned positive earth, I assume you are still using a generator/dynamo. In this case, a check of the voltage regulator may be worthwhile to see if the contacts are stuck which may lead to the battery discharging.

As the flashers/indicators only come to life with the ignition switched on, I would tend to think your problem lies elsewhere.

How did you go with your auto selector problem?

 

Ockham's razor: It's either the dynamo or the regulator.
JP

 

A brief update on this topic, having spent a few hours with the car at the weekend and discovering what I hope is the cause of the issue.

I have a copy of Tom's Jaguar Mk1/2 wiring schedule in colour (worth a donation - so useful) and worked my way out from the battery unplugging things. Fortunately the first thing I disconnect was the two fused circuits, so I quickly knew I had a problem in the live ignition-off circuits (brown as mentioned by red triangle).

I then had a bit of luck, in that whilst trying to find a screw in the footwell I spotted that the radio has the world's smallest LED on it and it was on! I don't think the radio had ever worked, and I reconnected it when putting the interior back together previously - it must have been on and I simply hadn't noticed. Turning it off, the LED went out and from what I can see from leaving it for a few hours, the battery is no longer draining.

So a simple one, and I wish I'd spotted it sooner so I hadn't missed the MOT slot(!), but at least it appears to be something simple. It had never crossed my mind that the radio could operate without the ignition on!

B

 

I have fitted a modern radio/CD player (Pioneer) which, when wired up following the instructions, is always "live" even when ignition is switched off. I presume current drain is very low, although I am uneasy about it for the reason you have alluded to.

Unfortunately, it is necessary to keep the radio unit "live" to retain station settings etc.