SOS - Electronic Distributor XJ6

(Ignacio) #1

Dear All,

After a one-year engine overhaul (only the block, crankshaft, head and camshafts remain), my 1978 automatic XJ6 4.2 Series 2 is almost ready to start its new life. A very professional workshop carried out the machining and reassembly and now, having had the engine delivered to my usual mechanic fitter, a last minute unexpected problem has popped up.
I was told to replace the mechanical distributor by an electronic type:
This is based upon the later Jaguar system. This is a brand new Lucas magnetic distributor with an externally mounted amplifier which is mounted on an alloy heat sink plate to eliminate problems due to heat. This distributor is already set up for the Jaguar that it will be fitted to so there is no need to change any settings. This kit is also supplied with a set of sealed for life carbon leads and a Lucas high output coil.

Well… the mechanic has made a mesh and the connections must be totally wrong - for what was supposed to be a plug-in solution - and now neither the fuel pump is working properly, nor the rev counter and some lights.
The question is that the new connections (looks like many old ones before used the negative of the coil) are not clear and, basically, the fitter is lost.
I have requested the support of the provider and I’m sure he will do his best (they always assisted very well before).
Probably the S2 electric connections should be modified when this distributor is fitted.
I would appreciate the assistance of anyone who knows about this and any picture or diagram that can show us what we are doing wrong.

Thank you very much for help.
Best regards,


(David Jauch) #2


The distributor connects to the amplifier with the large plug, two spade connectors go to the coil terminals. The rev counter pickup should be on a coil terminal. All Series Three 6-cyl. are equipped with it. Fuel pump and lights should be unrelated, but maybe - my guess - there is a common cause in the relay that turns on with the ignition, or in the ignition switch itself. It [ignition wiring] might be part of most Series III wiring diagrams you can find.
Hoping for the best,


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(Frank Andersen) #3

The 78/79 was a transition year between the SII and the SIII and Jaguar did some mix and match some SIIs were fitted with ‘some’ SIII features. We need to know if the dist actually was a mechanical points dist - and if you have fuel injection…

In principle, the 78 may have had original OPUS electronic system, or if it had plain points; the wiring present in the car may differ from the CE system.

However, the switch from any of them to the CE system should be straight forward. The kit should have the dist with a two-wire connector - connected to the CE amplifier. Which normally is bolted to the front of the intake manifold - acting as a heat sink…

There are two wires from the amp, white and white/black - the white goes to coil ‘+’, which also have the white power wire from the ign key. The white/black goes to coil ‘-’…

You now have ignition, sparking, while the engine is turning - it is that simple…:slight_smile:

Minor problems; the coil may have screw type connectors and the kit may have spades - or vice versa, to be converted. If you have fuel ignition; a white/black wire from the ECU is connected to coil ‘-’, and you now have injections…

The speedo; the early points version differs from later electronic speedos fitted - which were used for electronic ignition. In the early points dists, the coil ‘+’ was fed through the speedo - and this speedo type will not work directly with EI where the speedo ‘feed’ is from coil ‘-’…

The fuel pump issue may, as David says, be unrelated to the CE set-up unless you have fuel injection. Describe how the fuel pump malfunctions…

The light problem is certainly unrelated; the engine in and out of the car is bound to interfere unintentionally with wiring in the engine bay…


xj6 85 Sov Europe (UK/NZ)

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(Ignacio) #4

Great, Frank, thank you.
It’s an European car, fitted with carburators.
The pump and some other connections were earthed to the negative of the coil… and now some lights, the speed and the pump are not working properly now.
I’ll collect all the comments here and the reply from the supplier and I’ll pay a visit o the workshop today (or tomorrow, depending on the received feedback).
The main question is that if the electric connections vary when fitting the electronic distributor.
I appreciate your replies a lot.


(Frank Andersen) #5

Only the connections related to ignition itself, Ignacio…

Various devises were fitted through the years to protect the coil from overheating, including a resistor - sometimes incorporated using the starter relay to bypass the resistor during cranking. Not knowing exactly what versions you have got complicates matters…:slight_smile:

I assume that the you had the points distributor; one wire from the dist to the coil to be removed. The OPUS system had three wires at the dist - disconnect these wires from their terminals, and remove them.

The white/black wire from the CE ign amp goes to coil neg - this is the only wire connected to coil neg. Your coil pos may have another white/black - this must be disconnected. You may find a resistor in the coil pos wire coming from the ign switch - bypass it; connecting the resistor ‘in’ and ‘out’ wires together. Connecting the CE ign amp white wire to coil pos - in theory you should now have two white wires.

The ignition system is now configured for the CE system and you should have sparks with the engine cranking. No other electrics should be impaired - however, POs and other machinations may interfere as separate problems - to be addressed…

The problem with the fuel pump may be associated with the fuel safety relay. Which prevents the pumps from running unless ign key is in ‘crank’ position - or the engine is actually running with ign key to ‘on’. An oil pressure switch grounds the relay with oil pressure while the engine is running.

I suspect you have an electronic tacho (my previous post said speedo - senior moment!). In which case; the connecting wire should be white slate/blue - and should be connected to coil neg, for testing…

As an interim, to get the engine running - jumpwire the fuel pump…

xj6 85 Sov Europe (UK/NZ)

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(Ignacio) #6

Great help.
Thank you, Frank!!

(Ignacio) #7

Hello, again!

I provided the workshop the Haynes Manual books… but they said they cannot find the electrical wiring diagrams. Instead, they were using a sketch for the S3 injection engine… which I assume is part of the problem.
The dis supplier has sent me a sketch of the connection of the tacho, which has fixed the problem of the rev counter.
The pump connection is now pending, so I’m translating your previous post to Spanish for them.
If you had the S2 carburators electric diagram, I think we’d solve the problem finally.
Thanks a lot,


(Jochen Glöckner) #8


can’t help but everytime you write about the people you’re working with I’m feeling so sorry for you, as they always seem to mess up more than they ever fix …

The famous S57 pattern is for SIII cars. SII cars differ considerably. There is a full wiring pattern in the ROM at 86.40.

Unfortunately, the entire thing is b/w and all on one A4 page, but if you click on the pic twice it enlarges and the resolution is amazing. Maybe you can print it out on A3 or larger.

Best wishes


75 XJ6L 4.2 auto (UK spec)

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(Ignacio) #9

Thank you so much, Jochen.
Luckily, the machining workshop is a real good one.
The workshop in charge of the installation is the scaring one.
I hope now with the diagram you sent, they’ll connect the cables correctly. Otherwise, I’ll bring the Jag to an electrical workshop, but I’d prefer not to involve more parties for guarantee issues.
For the time being, after a year, and an overhaul that meant that only the block, crankshaft, head and camshafts are still “onboard”, I need it running, at least to convince my girlfriend that this wasn’t the worst investment ever.
After a Spit mk3, a GT6 and a TR4, still the TR4 has the worst record.
Thank you all for the support.
I promise pictures soon.


(Ignacio) #10

Sorry, Jochen, but the diagram is for injection Series 2, if I understand it welk. Would you have the carburetors one?
Thanks a lot!!

(Jochen Glöckner) #11

Don’t worry,

as I wrote earlier - the diagram isn’t a prime example of user-friendliness. It includes all versions over time (cf. items referred to as “early cars”) and markets (cf. items referred to as “Scandinavia only”) and options (cf. the AC circuit). So don’t get scared by the L jetronic circuit on the right side of the diagram. I spared you the next page relating to “Alternative circuits”. Here it comes

As you seem to spend an awful lot of time, money and nerves on this project - and obviously don’t have craftsmen you can rely on blindfolded - you should really get yourself the works documentation for your specific car. The SII ROM is still available for little money and worth every cent.

Good luck


75 XJ6L 4.2 auto (UK spec)

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(Frank Andersen) #12

The complication here is that even with correct connections, Ignacio; there may be a component failure…

What is actually the problem with the fuel pump reactions? With carbs the pump should not run with ign ‘on’ - but should run in ‘crank’. Which can be tested with the gear lever in ‘D’ - the pump should run, but the safety switch prevents cranking. Which saves some noise hassle…

With 20/20 hindsight; most conversions to CE or other electronic ignition are done with a running engine - eliminating some confusions…:slight_smile:

xj6 85 Sov Europe (UK/NZ)

(Ignacio) #13

Thanks a lot!
I provided them the Worskhop manual and Repair Operation Manual.
I think it should be therein…
I’ll anyway print the diagrams you sent me and visit them again.
Vielen Dank!

(Allan ) #14

Hi everyone,
I’ve also a series 3 Distributor and module for my XJC but I’m not going to fit that, I’ve opted for Lucas 45D6 with a Lucas sports coil from Powerspark ignition (

It looks completely standard and you only have to lose the ballast resistor.


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(Frank Andersen) #15

The crucial point is to identify the starter and fuel relays, Ignacio - where the relevant connections are…

xj6 85 Sov Europe (UK/NZ)

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(Ignacio) #16

Well, friends… after a visit to the workshop where the engine mounting is being done, now it’s clear I have to take out the car and bring it to a specialized electrical workshop.
An attached picture shows the situation:

  1. There are groups of cables hanging not connected (lower part of the picture). They were connected before to the terminals in the former (original) distributor, but the new one - according to the fitter - has not terminals to receive them (!).
  2. The cables for the ignition have been connected as you all explained in previous posts and according to the diagram sent by the supplier. However, when the key is turned, the engine makes a strange thing: it seems to start as “inverted” and it’s quite frightening (big noise and air blown through the air intake.
    However, the mechanical fitter showed me how - I hope my English is good enough to describe this - when the main terminal (the one that connects the key to the coil (marked as “main power terminal” in my pic) is disconnected and the key is turned, the mechanical approached several times the terminal to the coil and the engine finally started normally. I think there we have the critical problem.

Please, read though this explanation and let me know your thoughts.
I am concerned about sending the car to an electrical workshop who didn’t disconnect the system before and, now we have cables not connected (supposedly not related to the ignition) and a weird engine start when the coil is connected.
Anyway, I’m bringing the manuals, diagrams and your comments translated, so I hope a profesional workshop can finally settle this.
Your help is much appreciated.

Best regards,


(Frank Andersen) #17

This is what is confusing, Ignacio - the original mechanical points set-up should have one(!) connection - to coil neg…

With the original set-up I assume the engine started and ran as it should(?) - and the wires depicted served some function.

Which in principle should do the same when the CE was installed - with the original coil wire removed, replaced by the CE dist lead to the CE amp. With CE white/black to coil neg, and the CE white to coil pos…

After connecting the CE set-up as described; there should be one more wire connected to the coil pos - the ign key feed, white. This is all that is required for ignition; power to coil pos in ‘crank’ and ‘run’ - the white CE wire powering the ign amp, and CE white/black connecting coil neg to the ign amp…

Other wires shown are not related to ignition - but may relate to other functions. Identify wire colours and trace each wire - which may lead to the starter relay and the fuel pump relay, or whatever, and the wire colours will help to identify these items…

…which in turn may identify which wire diagrams are relevant - which is essential for correct connections. At present I don’t know that…:slight_smile:

xj6 85 Sov Europe (UK/NZ)

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(Frank Andersen) #18

This doesn’t make much sense, Ignacio - and it has no bearing on your English…:slight_smile:

Coil pos(!) must have power from the ign key, both in ‘crank’ and ‘run’ to ensure ignition - but coil pos has no relation to the operation of the starter relay/starter solenoid and starter motor. Given the original S2 (carbed) starter relay connections are somewhat complicated - and should be looked into. Cross connections may cause odd symptoms, depending on how they are cross connected. There is no ‘main power terminal’ at coil pos…
Instead there are two white wires from the ign key; one goes to starter relay C2 terminal - and is not related to the one going to coil pos. Ie, relay C2 must not be connected to coil pos. Relay W1 is powered from the ign key only in ‘crank’ by a separate wire - activating the relay, which operates the starter solenoid - which then engages the starter motor. A white/black wire connects the relay C1 to coil pos; this bypasses the coil ballast resistor during cranking - and both wire and resistor are redundant with the CE system fitted…

The crux is that whenever, or however, the starter solenoid has power it will engage the starter motor and crank the engine. So either the engine cranks as it should, ideally only with key to ‘crank’ - or it does not.

So there can be no ‘funny business’, engine misbehaviour due to the cranking action itself. The ‘big noise and air blown through the air intake’ is simple engine backfire. This may conceivable be due to misconnections of wires - causing ‘wild’ sparking. Or it may be caused by lean mixture - lack of fuel supply to the carbs. Ie, the problem is then with the fuel relay not running the pumps as they should.

Again, this may relate to wiring faults - and the fuel pump’s action should be observed. With ign ‘on’ there should be no pump action - the pumps should run in ‘crank’. To check this; put gear lever in ‘D’ - this should prevent actual cranking, and pump action should be audible.

Now, in the original S2 set-up an oil pressure switch is fitted to the engine block. This is a safety feature; when the engine is running the oil pressure switch engages the relay by grounding it. If the engine is not running, no oil pressure; the pump will not run with ign ‘on’ - in ‘crank’ this safety feature is bypassed…

The point here is that if the fuel pump is not reliably triggered; the carbs will have insufficient fuel - and the engine may backfire. The triggering of the fuel pump is not(!) meant to rely on coil pos connection - so manipulation of that should have no influence of pump action. To solve this the fuel relay should be located and the connections verified…

The back-firing, lack of fuel, may be related operation procedure during the testing - and a ‘one-off’ incident. But if manipulation of the coil pos connection influence fuelling; something is wrong with the electric connections…:slight_smile:

xj6 85 Sopv Europe (UK/NZ)

(Ignacio) #19

Well… months after the engine overhaul, he situation is as follows:

  • the engine has the same pressure in all the cylinders (9 bar)
  • the gear that connects the distributor had slipped one tooth, and that’s why the sparking was wrong. The distributor head has been adapted to this, to avoid reopening the engine.

However, before the engine rebuild, the problem was that, at about 3000rpm, there were continuous destinations.
Now, the engine goes very smooth, but at about 3000rpn, it detonated again and does not stop until the speed is decreased.
A lot of gasoline is unburnt, which makes us think there’s still an electrical problem.
Otherwise, the carburetors, which have also been overhauled, could be involved in this.
Any idea?

Thank you in advance and best regards,


(Frank Andersen) #20

Detonation means too high advance for the fuel octane used, Ignacio - the advance must be backed off further…

However, if the advance is set to specs; the dist fitted may give too much advance as revs rise. Again the remedy is to ‘back off’ advance setting. It’s a bit complicated; ‘pinking’ relates both to manifold pressure (cylinder fill) and centrifugal advance. Closing the throttle reduces manifold pressure (increases vacuum); which reduces cylinder fill, which is a cause of detonation…

Unburnt fuel means the engine is running fat, or misfiring - which should be irrelevant for ‘pinking’/detonation. However, ‘pinking’ is unburnt fuel detonating due to high cylinder pressure and temp (caused by too much advance) - fat running increases the ‘violence’ of detonations due to more fuel detonating - but is not the cause of pinking.

As a test; disconnect and clamp the vacuum hose to the distributor. This will eliminate vacuum influencing advance - which may or may not change the pinking situation…

Fat running is a carb or AED issue - to be addressed as required…

xj6 85 Sov Europe (UK/NZ)

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