A few electrical gremlins

Dear all,

Just got my XJC back following Euro bumper conversion blocks great).

A couple of gripes (one related, the second pre-existing) where I would appreciate some guidance:

Left sidelight does not come on. This is of course a new addition following the conversion. It worked in the shop but no longer. Left headlight was also not working last night but following fiddling with the connections around the lighting fuse box, now works. But still no sidelight. Any ideas welcome.

Battery drain. I was suffering repeated rapid battery drain (all gone within 48 hours), traced problem to Fuse 3 under steering column (interior lighting and radio aerial). Removed fuse and no issue. But how do I trace the underlying fault? As it would be nice to have interior lighting at some point.

On a related note, when I plugged a USB charger into the cigar lighter, there was a distinct rapid ticking coming from around the fuse box. Cigar lighter seems dead now.

As ever, any tips much appreciated.

Many thanks

Nick HILL, XJC 4.2 (1976), Canadian spec Euro bumpers.

Don’t trust the fuses.
Side light, is that the one inside the headlights? It’s either a ground or a red green wire, the circuit is completely separate from the headlights from the light switch onwards, but it could still be a fuse (if the sidelights are fused), or a junction. Or the bulb!

The fuse holders are terrible and sometimes, if three of the four prongs make good contact with the fuse, that is not enough.

The aerial and the sidelights and the radio work together in a very strange way. At least on the S3.

A cigar lighter should not die from a little usb charger. Does the actual lighter still work? No idea what the ticking could have been. Arcing?

Good luck

As David says, Nick - the fuse box(es) is/are no great; bad connections may overheat and distort the boxes. Leading to more bad connections and so on. Since the sidelights are add-ons, only the shop knows how it is connected. You have to access the bulb and bulb holder to check for power/ground - and the bulb itself…

Battery leakdown is obviously caused by ‘something’ drawing current, and seemingly over the #3 fuse circuit; discharge over 48 hours imply a 5W bulb. Disconnect a battery clamp and measure current between battery post and clamp; it should read some 0,5A if so. Normal drain would be 35mA - clock and radio standby. Observe for any lit lamps, battery connected, of course - and just for fun; remove boot light bulb; a frequent culprit…

Long process; disconnect a battery clamp and connect a test lamp between the clamp and battery post. With the leak present, the lamp will be lit - and you can observe effect of actions (bulb removals etc) by test lamp unlit when the culprit is found…

xj6 85 Sov Europe (UK/NZ)

If your Jaguar is old enough to have those glass tube fuses, one of the best things you can do for your car is to unbolt each fuse box, roll it over and carefully flow some solder into each one of the crimped wire connectors. It’s a myth that a crimped connection is reliable.

Ok thank you all. I am installing new h4 headlights today so will have a look at connections and fuses. The sidelights are European style, not within the headlight sensor.



the job is quite easy, if you also have the 7" outer rims for the outboard lights. While the power wires are easy to install and check, the ground wires per factory run to connectors at the radiator carrier. More often the grounds are a cause of grievance …

Good luck


75 XJ6L 4.2 auto (UK spec)

As so often, oddly simple: bulb blown. Must admit I hadn’t expected a brand new lamp unit to blow the bulb almost immediately. New headlamps installed.

Still need to trace the fault causing battery drain.



Not if properly done: it’s indicative that crimping is an aviation standard.

My cousin is an electrical engineer that works for the Airforce and IIRC has told me that the Aviation standard is the combination of the two, i;e. it must be a mechanical joint (crimped) and a chemical joint (solder or whatever).

It’s an old debate and if it feels secure it will last for many years no matter what.

Thanks again all.

Sidelight fixed but gremlin remains in left hand headlight which is much less bright than the right hand and is intermittent.

Have gone over all the contacts around the headlamp fuses and relay, giving them a bit of a rub and contact cleaner but without success so far…



Did you check the grounds? Also with the lights on wiggle everywhere and see if anything helps.

Thanks, I did find a bad ground, linked to the LH inner headlight. Now a good ground, which led to a marginal improvement but LH outer headlight is still dim.

Frustratingly, there was a fleeting moment when I got bright white light from this light. But it lasted only a few seconds and despite my best wiggling I was unable to reproduce this. My fuses are good, with no resistance between the fuse terminals and the relay.

I did notice that the wiring layout for the LH headlight fuses was inverted from the RH one. But this just meant that the main beams were running on the 10A fuse instead of the 25A one. So I swapped that back.

One other thing though, when I switched to full beams, the LH outer headlight dims further. Why would that be? Surely it should be brighter?

Is there another, separate outer headlight ground somewhere I am missing?

It seems to me there is something amiss in the wiring but I cannot see what. The headlamp units are brand new.



Hmm. Resistance in the wiring inside the wing maybe?
The fuse box itself is usually the biggest problem, followed by bad grounds and fuses that look good but aren’t. Since outer high beams are fused and wired separately where it matters it kind of has to be the ground.

Gotcha. Insufficient tension in the the spade connections behind the headlight itself. So sometimes one connection, sometimes none. All good now, which is a relief as I wasn’t looking forward to driving by candlelight later.
Thanks all

1 Like

Question, Nick - are you sure the outer LH is on high beam?

What exactly did you do at the fuse box? Blue/red is low beam from the relay into the fuse box - to the two low beam, left and right, 10A fuses. From the fuse box, the 10A fuses goes to the outer low beam bulbs. The blue/white likewise goes from the relay to the two, left and right, 25A fuses - and respectively to the high beam bulbs. Changing wiring on one side of the fuse box without changing on the other side is wrong - unless the connections were wrong from the start. It is a bit puzzling that a 10A did not blow if subjected to the current requirement of the two high beam bulbs…

Bearing in mind that wiring/fuses are respectively; left low/right low/left/left high/right high - are you sure wiring is in accord? And that the left inner and left outer high is wired in parallel and not in series.

All that said; have you checked/changed the left outer bulb - it may have failed in an unusual manner. Or indeed, the bulb holder itself may have an anomaly, like a bad ground? It’s not entirely clear to me whether both inner and outer high is dim - or indeed what happens the the relay is in low beam…?

xj6 85 Sov Europe (UK/NZ)

From my recollection of mil-stan-217 soldering and crimping were banned.
If a soldered wire was crimped the solder relaxing over time would cause the joint to fail
If a crimped joint was to be soldered then the heat would compromise the tension of the crimp and the soldered wire to be susceptible to breaking with vibration
Maybe it’s changed but I don’t remember any crimped joint being soldered during my past life as a QA manager
Doesn’t mean I haven’t soldered crimps in the past on personal projects! But put some mechanical support eg adhesive lined heatshrink afterwards


Frank, it didn’t make any difference as the PO had left 25A fuses for each. So my comment was really a red herring, all I did in effect was put the correct 10A fuse in the dipped beam fuseholder and then changed the wiring accordingly so that the fuses were appropriate to the current.

Anyway all is good now. Dipped beams and full beams, LH and RH.

Crimping might be reliable only if both the wire and the terminal are corrosion resistant, or the entire connection is protected from the elements. None of that is the case in 1980’s Jaguars. Solder or forever be chasing gremlins.

He may have said that a soldered joint must have mechanical support e.g. by taped loom or glue to provide stress relief.