Bertrand, just so you are aware, you can reply to all the people that have suggested things in the same post. Just identify who you are talking to. It will save multi posts.
Think + 
If you follow the simple advice step by step, you will attain the desired result via further advices
electrical work is intimidating , even if you are used to it,
I personally dislike steering column auto electrics 
Ah OK, I am a rookie with forums !!
Well, I am now getting quite confused…
I have 3 wires connected to the coil:
One black on the “+” side and 2 x Black and white on the “-” side.
Trying to jump Battery “+” with coil “+” is short circuiting. After measurement I read that Coil “+” is actually a “-” !!! if I disconnect the B/W wires connecte onto coil “-” I have 0V.
I then checked all wires to the coil:
Black wire is a negative and exhibits 12.5V (battery voltage) when connected to battery"+"
Is it possible I have misconnected the coil ?
B/W wire is also a negative and exhibits 12.5 V when connected to battery “+”
All the above measurements have been done key off.
One or two or more points:
-
Black is usually ground. Why it is attached to the+ post on the coil astounds me.
-
I suspect the contacts on the points are corroded. if so, the ground leg of the circuit is always open/ Nothing will check out, much less fire the spark plugs!!!
-
Teh ballast coil is a resistor. 12 v in, less out in the run ppsition of the ignition switch.
-
The ballast coil aka resistor is by passed with the key in crank position.
-
Before i had a meter, i now have three, all a bit different, I used a simple test light. AStill have and at times, use, about three.
-
Make one Any small 12 v bulb. Solder a wire to the tip. That is for +. Solder NOTHER WIRE TO THE BRASS BASE. THAT IS -.
7 Do you have the wire schematic for your car. i see them as essential. Could not get along without mine.
No problem if you look at the top of the page you will see your avatar, there should be a 
click on that.
**
This not according to wiring diagrams, Bertrand…
You have to first identify coil terminals correctly by the terminal markings - then sort out the wire colors. Which may may pose a problem - they don’t gel with any of my diagrams.
Trace the wire from the distributor to the coil - whatever its color; it goes to coil terminal marked ‘-’. This wire is connected to the points - which ‘makes’ and ‘breaks’ the coil ‘-’ connection to ground. Do not connect any of the other wires to coil positive, but jumpwire coil ‘+’ to battery. With the points open; you should now have 12V on both coil ‘+’ and ‘-’, and when cranking; you should have spark - and the engine should start…
Next; remove jumpwire and check the other wires; with ign ‘off’ there should be no power on any wire or coil terminals…
The other wires. Carl is absolutely right; in Jaguar wiring logic, black is invariably direct ground and has no business at any coil terminal. However, if the wire from the distributor is indeed black - so be it, but make absolutely sure!
Normally; with two wires to be connected to coil ‘+’, one comes from the ign key, powered with ign ‘on’ through the tachometer and external resistor. The other wire would come from the starter relay, which also acts as a resistor bypass - or some ‘device’ which only powers that wire with ign to crank. They can be tested for power with the ign key in the respective positions.
The question is which set-up you have. The ‘normal’ Jguar wire color was white (ign key) to coil ‘+’ and white/black (distributor) to coil ‘-’. So it is of some concern; ideally the wires should be traced to their origins. One wire (black/white?) should go to an external coil resistor - the other wire on the resistor should then be white. The other wire, which normally should be white/blue, goes to a ‘bypass’ device - possibly the starter relay.
These two wires, ign key and ‘bypass’, should be connected to coil ‘+’, but disregarding their colors; one should be powered with ign ‘on’ - and both powered with ign to ‘crank’…
The presence of the black wire is an anomaly; it should show ‘0’ ohms at any time, and should theoretically be irrelevant to the ignition system - but POs sometimes do the strangest things…
Reading through this takes longer than actually doing the tests; as Carl also says - a multimeter is mandatory, together with a test lamp, (and knowing how to use them) whenever working with car electrics!
To summarize; while cranking the external resistor is bypassed - this gives higher coil current during cranking for more spark power. While running, the resistor limits coil current, but also; if points are closed with the engine stoppped and ign is ‘on’ - the resistor prevents coil burn-out.
Frank
xj6 85 Sov Europe (UK/NZ)
Hi Mike,
If I do that it is short circuited…It works only if I disconnect the “-” side
From what you have said
To see if you have some anomaly in coil connection
(I know you have a multimeter)
disconnect battery + terminal
disconnect the wire you say is attached coil + and shorting
test the resistance between it and earth on the car, battery terminal etc
It should be very high, not just a few ohms.
If it is low, its wrongly connected or has a bare patch causing a direct short
these are easy tests, if you pass each one, move on to the next
Thanks Tony,will do and keep you posted !
Bert!
Go from one item to the next, you must have voltage starting from the
ignition switch.
Walter
**
On a S1 there is no conceivable reason for having two co-connected wires to coil ‘-’, Bertrand; those two wires are at coil ‘+’, repeat,coil ‘+’. The single wire connector is coil ‘-’, unless proven marked otherwise - and that single wire goes to distributor points.
There should be no ‘short’ if you then jumpwire 12V directly to coil ‘+’ - the current is then limited by coil primary resistance even with the points closed. However, you should measure coil primary resistance, wires disconnected, to verify that the coil has a resistance of some 2 ohms, give or take tad. Which confirms that there are no shorts, 0 or very low resistance, within the coil - which would mean the coil is defective and cannot deliver ignition voltages. (pleas, confirm coil resistance!)
The coil is not harmed with direct 12V applied - unless the connection is long/permanent, as Paul says. The test lamp, between coil ‘-’ and ground, will flicker when cranking - and coil center lead can be used to verify spark, as described by Kevin and Tony. This is a direct check of the coil/points - if center lead is sparking but not the plugs; the coil is OK, and where the spark goes AWOL is then to be investigated…
The other picture shows the external coil resistor, and the wire colors (which are none to clear either) may be informative. Measure its resistance with the wires disconnected, and tell us…
Frank
xj6 85 Sov Europe (UK/NZ)
Hi Everyone,
OK so my coil is not properly connected ist it? Should I rotate it 180°? Please confirm on which pole B/W wires should be connected Positive or negative connectors on the coil ?
Coil resistance is 1.4 Ohms so it should be OK
Ballast resistor is at 1.7 Ohms, so it should be OK
When you talk about verifying points continuity is it the lead connected to the distributor side (see photo) ?
I have redone some voltage measurements again
Ignition off:
Black lead to battery positive 0V
Black lead to battery negative 0V
Black/white lead to battery positive 0V
White/Black lead to battery positive 12.6V
Distributor lead to battery positive 12.6V
Now Ingnition on:
Black lead to battery positive 0V
Black lead to battery negative 0V
Black/white lead to battery positive 0V
White/Black lead to battery positive 12.6V
Distributor lead to battery positive 12.6V
So it is absolutely identical… 
The black lead is continuous between the distributor and the coil and the balast resistor
More I dig less I understand !!!
Hi Frank,
Comments on the lead colour dragged my attention and I started to strip the harness to identify the real colours of the leads.
The one I called “Black” hooked on the positive terminal of the coil is actually White/Blue (W/U on the diagram). It goes to C1 terminal on the 22RA Relay bolted on the firewall, continuity is good.
The White Black lead connected to the “-” terminal of the coil goes to the distributor side as shown in my previous message and the continuity is good. Every metallic parts shown on the open distributor are grounded but the rotor.
I’ll keep crawling in the wiring diagram to try to find something wrong…In the meantime any comments appreciated !!
Thanks
Bertrand
Bertrand,
sorry, been away for some time, hence didn’t answer.
May I suggest that you first check your starting point of any fault finding? To do so, you should try to get hold of as much documentation of your car as possible. BTW, this is why I asked about the state of the car. The Repair Operation Manual and the Parts Catalogue are incredible sources of information. Folks on this list are extremely helpful and an amazing bunch - yours truly not included, of course -, but it is a lot easier to communicate if you have made yourself an idea of what’s going on …
Early cars had coils without ballast resistors; later cars used ballast resistors for better performance at high revs and better cold starting. Check out which one you’ve got. The reference VINs are indicated in the lower part of the page.
These are the corresponding wiring schemes - the first one for ignitions without ballast resistor.
Maybe you can get something out of them; if you click on the pics you should be able to enlarge to a useful size.
If I understand correctly the coil is in the top right corner with a white/black wire taking to the distributor and a white wire to the tacho.
This is the later series with ballast resistor:
White/blue: starter solenoid switch to coil
White/yellow: ballast resistor (if you have one) to coil
White: ignition switch to tach
White: coil to tach
White/black: coil to distributor
black: distributor to ground
So in my scheme there is no direct ground wire at the coil!
Your strange figures make me suspicious your system might be mismatching a regular coil with a ballast resistor - or the other way round.
Good luck
Jochen
75 XJ6L 4.2 auto (UK spec)
1 Like
Thanks Jöchen,
I have work in my plate !
I’ll let you know
BTW I don’t know if anything has been changed on the car, electricity wise. I only know that it’s a second hand car my father bought in 1976
**
The ‘two-tab’ connector is coil ‘+’, Bertrand - the single tab is coil ‘-’. So white/blue is indeed connected between coil ‘+’ and C1 on the 22RA relay - which is the starter relay. As the key is turned to ‘crank’, the relay operates by ign key power, and W1 is powering coil ‘+’ from ign key. (W4 is simultaneously connected to the starter solenoid, cranking the engine)
Caution! Coil ‘-’ should never(!) be connected directly to battery ‘+’, it invites disaster…
The correct test to verify that W1 has power in ‘crank’ (preferably with test lamp) - and disconnected from coil ‘+’. With ign ‘on’ there should be no power on W1, but coil ‘+’ is powered from ign key through the tacho and the external coil resistor.
Secondary tests, assuming points are open - with ign ‘on’ both the coil '+ and ‘-’ should have 12V (battery voltage), as should both ends of the external coil resistor. In this situation no current is flowing through the coil - if points are closed; other voltages are read as current is flowing.
Ohming between two measuring measuring points reads the resistance; ‘0’ means continuity - otherwise it shows the resistance in between the measuring points. For consistency; at least one measuring point/connection must be disconnected from the car wiring. If wires are connected; the ohmmeter shows a combination of the ‘short way resistance’ between the measuring point - and the ‘long way resistance’ through the car wiring. And the measuring is misleading…
As an aside, all wiring winds up in chassis ground, and while ultimately winding up at battery ‘-’ post; wires are connected to the chassis. So a bad ground may not show up in ohming to battery ‘+’ - which may or may not be relevant.
Your coil and resistor resistances looks normal, given correct ohming procedures. As do indeed your picture of the dist’s innards - and given that the points gap is set to 0.014 - 0.016" and voltage readings are as described, there should be sparking on coil center lead…
Frank
xj6 85 Sov Europe (UK/NZ)