Since the day I bought my '85 XJ6 ,the instrument panel lights haven't worked.
I pulled the Rheostat and opened it to find it had burnt out.Then I replaced it with another one,only to watch it glow red hot and also burn out.
I then by-passed it altogether,now they work until I turn the ignition on.When I do that it blows the number 8 fuse.
I'm no auto elec dude, but would it be a ground issue?
I've read people talking about a redundant lead,but I'm not sure from where to where it should go.

Any help would much appreciated as this is doing my head in.Cheers.

 

Not a ground as such, but an unintended ground. AKA a "short".


The Jaguar schematic S57 is an absolute necessity for owners of these cars. Get one !!!


The gauges are ignition on fed. So, somewhere along the path of the white wire to that fuse panel the insulation might be bad and touching metal.


Or beyond that fuse panel is another wire. I don't have the color here.
It goes to the rheostat. Same possible problem, bare wire in contact with metal.


I'm fascinated that you could remove the rheostat!! My guage lights went dark. I was going to merely jump the rheostat. But, I got lucky!!! I sprayed it with contact cleaner as best as I could and excercised it. Eureka, the lights came on. At best, they are far from bright...


Carl

 

i gave up trying to fix mine and now run a wire from the back of the headlight switch so the dash lights come on at the first click[side lights]of the dial

 

Thanks Carl and hooter.
I've had a bit of a look from underneath the dash at the but couldn't see any obvious culprit.I will probably take the dash off ( which I was trying not to do)for a clearer view.
There are a few unnecessary wires that need proper looking at and previous owner alterations (connections) to be inspected as well.
I do have a schematic chart and am learning that also.Sometimes it's easier to hear someone explain, rather than look at the map and scratch your head and say, clear as mud.

I took a couple of pics of the guts of the Rheostat for future reference.You just need to unscrew the two connector screws and lift the three tabs.
You will see the dark section is where my problem is.Wondering If I soldered it ,would that resurrect it?

 

I can't quite make out the top photo. The other two are very "illuminating". Sorry, I could not resist.


That "dark spot" is melted solder! Someone wither spliced a wire and the solder dripped, or more sinister, a bare soldered splice touched here, and shorted to ground.


The last picture nicely shows the coiled wire. That wire is resistant. The knob turns an arm that travels along that resistance wire. Thusly, resistance is added to the electrical path from the fuse to the
guage lights. At one end, direct, no resistance. Lights bright. Turn the knob and more resistance wire is included in the path and the lights dim.


At one time, that might have been OK. But, with he passage of time, the resistance value has probably increased. Result, much dimmer,.


I've decided to accept mine as a mere on/off switch!!


If the schematic you have is the Haynes version, put it away. Probably great for an EE. Just confused me and probably others.


OTH, peruse the S57. Color codes for wires. A more or less standard Brit scheme. Identification of the symbols on the drawings. Switch, connector, resistor, diode, etc.


And the pages depict the location of components, at least some of them.


Then, each page relates to a system. The electricl paths can be identified. Example. The ignition switch has both brown and white wires. Brown depicts "always hot". White, hot only with the switch. Voila, power in, switch on, power out!!!



On further musing on the picture of the "Variable resistor" Aka rheostat, I see evidence of a bad connection with the arm. What does the arm look like"? Burnt, as well, I suspect!!!


Solder fix that, yeah, sorta, but practical, naaah.
ditch it or replace it.


I am intrigued by the direct path. Lights on, guage lights come on!!!


In other cars, one might wish to dim them to eliminate glare. Here,
Ha!!!


Carl

 

there are two black ground wires that are connected to tabs exactly under the alternator / battery Gage, and above the headlights Switch. They seem to be Ground-continuity wires so that if one is disconnected from its tab, the entire array of gage lights go off. To check, remove the under-dash cover and use a mirror and light to look between the top of the headlights switch and the bottom of the battery gage, difficult to see so maybe using your phone camera might help. Removing the dimmer-rheostat only leads to more problems as you already know. keep it original.

 

I have taken the liberty of downloading your Excellent photo of the top side of the dimmer and have labeled the spades as they appear in my car.

As far as I know they're stock, original colors for a Series 2.


I have 3 female spades holding 4 wires connected to my dimmer; one female spade holds 2 (TWO) Red/White wires. That's the label, "2 Red/White wires," nearest the viewer. These are power from the Battery.

The spades are connected inside the switch so it doesn't matter if the wires are on the upper or lower male spade -At least that's how my car is.

On the other side of the rheostat it Does matter which wire is where!

The middle male spade in this picture holds a single Brown/Red wire; the one with the arrow labeled, "1 Brown/Red wire." Power to this wire is effected by the position of the rheostat wiper; it dims the dash lights, or not depending on position of the wiper.

The remaining male spade connector (top of the photo) holds a single Red/White wire. This powers the Opticell which is Never dimmed (it's quite dim enough under full power. This is why LEDs [not usually dimmable] work so well as Opticell replacements).

Series 3 cars may have different wire colors, but I'm sure the construction of the rheostat is the same.
(';')

 

Bypassing the rheostat, in and of itself, should cause no problems. I ran my XJS and previous Series III that way for years with no problems. The benefit was brighter panel lights.

There should be no tie-in between ignition switched power and the panel light circuit.

In passing the rheostat I assume you joined all the wires together, right? Three wires, probably? What are the colors, just out of curiosity? They should be red/blue and red/white

Anyhow, disconnect the wires, install new fuse, turn key on. Now re-join the wires one by one. Whichever one makes the fuse blow marks the beginning of the trail to finding the short

Cheers
DD

 

They both were still connected.Thanks anyway,Jose.

 

Yes, 3 wires.2 blue /red wires together and 1 red/white wire.



As I don't have anymore Rheostats left, I cant try out your method of testing.

I have pulled the dash off and can't see any problems with bare wires touching bare metal.I did take out a handful of wires and such that I believe to be the remains of a car alarm.Also, all of them were spliced into several original wires,including the white and brown to the back of the ignition using those connectors that you put new wire along side the one you want tap into.So basically it pierces the two without cutting the main.
Not sure if that method has damaged the original wires too much?

Might have to go and buy a circuit tester to pin-point the problem.

Mark.

 

Doug:


Interesting. I could've swore that I needed the ignition switch
on to get dash lights. As well as the head lamps. aaaaah,
I thought I had it figured out. But, on the last outting, the
guage lights still worked. I guess that is what counts...


Mark.


That blue wire in your great picture is a "stranger". A PO
has been there. It jumps the rheostat. But, I have this "funny"
feeling that it jumps the "wrong" spades. No clear on this, though.
If so, that might just be the "short"!!!!


Good guess on the alarm butchery. Removal is a major improvement.


Mine had a really crude one. It didn't even work. Good thing, it caused no harm!!! I removed it forthwith.


Carl

 

EDIT: Never mind.
(';')

 

Carl and Mark,

the Series 3 parking lights / dash lights / and headlights are sort of "self powered" by the Main Lights switch, don't know about the Series 2 cars up to 1979. The thick Brown wire from the Main Lights Switch is connected to the driver's side Firewall Post (LHD cars), which is hot all the time.

but you need the ignition ON for the Reverse lights / Turn Signal lights, and Stop lights, again in Series 3 cars.

Remove that blue Jumper cable and see what happens?? Could be that is where the problem is that is blowing the fuse, like Carl said.

 

Separate the two red/blue wires.

Turn key on

Touch the red/white to one of the red/blue. Does the fuse blow?

Now touch the red/white to the other red/blue. Does the fuse blow?

Whichever makes the fuse blow, that's the 'leg' you have to track down


I doubt it....although that type of joiner/splicer can sometimes cause problems, yes.

Cheers
DD

 

Sort of.

The blue wire by passes the rheostat, which in and of itself is perfectly OK. The problem is upstream or downstream of the bypass.....which is probably what wrecked the rheostats.

The tie-in to ignition switched power is very odd, possibly related to the previous wiring mods.

Cheers
DD

 

Thanks guys for being so helpful.

For the life of me ,I cannot see anything wrong or out of place with the wiring (apart from crap that was attached to it/ alarm).

I will try what you suggested.

Just a pic to show you guys I'm not just sticking my head under the dash.
The following scene might make some people cringe,so for those people, LOOK AWAY NOW!!!!!!!!

 

Look at the wires at the back of the Main Lights switch. Position 1 is Off. Position 2 is Parking / Side, and Gauge lights. That wire is the one you need to check for continuity to the dimmer-rheostat. Remember the Thick Brown wire is always hot, don't touch the brown wire switch's contact with a tool or metal, disconnect the battery if removing switch. Your dimmer has 3 or 4 male spades? Or you only have 3 femaled spaded wires? I have a spare dimmer removed from a 1986 and it has 4 male spades, identical to the June 1983 build date part in my 1984 model XJ6.

 

does your lights switch look like this??

 

Ok,One blue/ red wire that taps into that connection goes to the cigar lighter and when touch with the red/white wire does nothing.The other blue /red wire goes back to under the dash ,and when touched with the red/white wire (with ignition turned on) blows the fuse.

I've tracked that wire to where it enters the taped bundle of wires and seems fine.

Power is only coming through the red/blue.Both times with just lights on and with lights and ignition on......It did blow the fuse when the red/blue wire accidently touched the gear stick.

 

The dimmer looks identical.
I haven't cut the tape off the main body of wires and the wires to the center console as I'm doing the easier checks first.

The main lighting switch I have is different to yours.

Looking at the Schematic,to me,there is only one route....Ignition>Inverter>Panel lights>Rheostat>Lighting switch....don't know if I'm reading it right but if so,where would I find the Inverter and what does it look like?