Jaguar Repair: XJ6 headlamps, e-type tachometer, ballast resistor, intermittent faults

Question
QUESTION: Howard,

 The headlamps stopped working on my 84 XJ6.  I tested the fuses on the left inner fender, & cleaned the connectors on the relay.  The high beam works and turns on all 4 lights when the headlight switch is all the way up, if the headlamp switch is only on the parking lights the high beam only works if you hold the stalk switch which is normal flasher mode.  So I think the headlight switch is probably ok - do you think the problem is with the relay ?  

 My 73 e-type tachometer is becoming erratic.  Sometimes it's fine, sometimes it reads a steady 500 rpm below what I know the engine is at and sometimes the needle jumps up and down.  I read it's connected to the ballast resistor - I suppose that's connected to the coil ?  Could the problem be there or is it the tach ?

 Thanks,

 Steve.

ANSWER: Hi Steve,

The High/Low beam is by the lever pushed forward or back and then pulled back against the spring to flash High beam. If your high beam and high beam flash is operating ok and only Low beam is failing you need to go to the under the hood fuse box and test for power on both sides of each fuse while operating the low beam. Fuse #2 and #4 receive power in Low beam from the relay (located just back from the fuse box.)

If there is no power there when Low beam is selected check the relay with a test light.
The relay makes a "Click" that is easily heard when under the hood when High/Low beam it selected. However, that don't mean that it made the connection so you may have to unbolt the relay so as to gain access to the pins and with a test light check pin #56b (Blue w/Red tracer wire on it) as it supplies power to the Low beams in the fuse box.

On the "E" Type if it is a 4.2 "E", the tach generator (mounted on the rear of the intake cam) operates the tach and the two wires have no connection with the electrical system of the car.

Intermittent faults are very difficult to trace. The only way I know of to pin point the problem is to use either a high end volt meter (they can read voltages without interrupting a signal) or a Logic Probe. One more option would be to do what I had done years ago and that is to get a LED and make long leads and connect the leads to the two pins on the tach generator itself along with the tach leads and put the LED on the dash so you can monitor the flash as you drive to see if the generator is at fault and if the generator is still flashing at the time the tach fails move the wires of the LED to the wire ends at the tach and again if the tach dies and the LED keeps flashing then you know it is the tach itself.

If your "E" is a V-12 I can't help as I don't have a diagram and don't remember how the tach is wired.

Howard

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resistor  
Wire to tach   QUESTION: Howard,

   I had another look at the fuses, #2 & #4 as you mentioned.  Number 4 was somewhat loose and wiggling it got the lights on !  So I bent the holders in a bit, I wish all fixes were that easy !!

   Regarding the e-type tach, I have a V12 and the manual mentions it's connected to the ballast resistor so runs off pulses from the negative side of the coil.  I had a look and the resistor is under a metal cover underneath the coil.  But on my car the cable to the tach doesn't go thru the resistor, it comes off the negative terminal of the coil and goes through a splitter with the other cable going to the ignition amplifier.  The wire to the tach passes thru a small black resistor of some sort then goes to the tach.  I attached a photo.  When I pulled this cable the tach went dead, I cleaned the connectors so I think my problems were dirty connectors or maybe that little resistor is going bad.

   Thanks again Howard,

   Steve.

ANSWER: Hi Steve,

The V-12 went through some changes as I remember. We had to remove the existing ignition system on some and put a circuit board inside the distributor just under the rotor. This was a modification from Jaguar. I don't remember which models were affected and I didn't save any of the written data on it. I don't remember it changing the tach connection though.

I looked through my service bulletins and service training manuals from Jaguar but the only thing I found on the ignition was a diagram of the Opus-Lucas system and it didn't show the tach connection.

I never seen a resistor on the negative side of a coil. Look at your wiring diagram to see if the resistor don't belong on the positive side of the coil. Also look to see if there is just one connection on the tach or two. If there are two then it is like an MG and the power to the coil goes through the tach to get to the coil. (odd system but Lucas did that on the MG) Most other brands of cars take the tach signal off of the negative side of the coil but I don't remember how the V-12 did it but your wiring diagram will show that.

Howard

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V12 ignition  

Broken hub fulcrum rod   QUESTION: Howard,

   The wire with the resistor comes off the left post of the coil, I think it was negative.  I've attached a drawing for the V12 ignition but like I said, my layout is slightly different.  I discovered a problem with my XJ6 today, I suspected the right rear tire had some toe in, I noticed I have to keep my steering wheel a bit to the left to drive straight.  I crawled under to have a look - check out my photo -I guess I need a new hub !  The fulcrum rod bearings are exposed on the rear side, I don't think I'll drive it till a get another hub.  

 Thanks again Howard,

 Steve.

Answer
On the diagram if that is what your amplifier looks like then you should be wired the same. I have that diagram but it is listed for the XJ-12 sedan in my book. Not that it is not for the "E" type too. As for the coil, you can't count on left/right pin position as the coil can rotate in the holder. All coils are marked (+) and (-) And the polarity is always set by the battery polarity on all systems.

Yes, I see the alloy hub is broken and is dangerous to drive like that as it could come further apart and cause you to loose control of the car. You should check the part number of the alloy piece and check with several of the parts companies to see if that part is the same on all of the Jags of that span of years as I believe they are all the same. If the numbers confirm that, You should be able to find a salvage company that will sell that. The salvage companies will not strip the unit and will want to sell the alloy hub with the stub axle and bearings as a unit but that will probably still be cheaper then a new alloy hub. I think it would be better to get a whole unit (if it is a good one with bearings and all) because it is expensive and a lot of work to set up the bearings in that hub. Read your manual on that and you will see what I mean, I have done a few of them and it requires a stock of shims and a press to do it. I use a piece of 3/4" threaded rod with spacers to set the preload on the wheel bearings so I don't have to use the axle.

Howard