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Jaguar Repair/1977 xj6L will not start


QUESTION: Just purchased this vehicle. Has been starting just fine and runs well. Had just properly installed the air filter in housing. It had not been closed up properly. Started the motor as a check. Then noticed the cabin panel under the ignition switch was not secured and did a little pushing prodding and by feel looking for a connector to secure it. Discovered the reostat for the dash lights think inking at first it was the fastener I wsd looking for. After turning the knob and it not driving home I looked and discovered the rheostat. As it was getting dark I decided to wait but wanted to see how the car ran with the air filter properly instalked . Turned the ignition switch numerous times...nothing but a barely discernable click from the dashboard...battery was fully charged yesterday. Headlights work. Radio won't with key on accessory.
Could the ignition switch have failed that quickly? Thank you for your consideration. David

ANSWER: Hi David,

You seem to have several electrical issues at the same time. Working in several Jaguar dealerships I learned that when faced with several electrical problems that symptoms rarely tell you what is wrong other then to give you a list to go by.

I learned to trace only one circuit at a time. Some mechanics start at the power and trace one joint at a time toward the Load (item that don't operate) However, I prefer to start at the load and with a test light and a wiring diagram and test each joint headed toward the power supply (battery) Often when I find the fault in that one circuit, it corrects the other circuits fault also. If not, after I correct one circuit I just pick the next circuit that has failed and repeat the process. In dealerships we were paid by commission so we only got paid for results not just work.

In your case you have several circuits failed so I would start with the Starter motor circuit as it is a simple circuit to follow. You have block out of your mind that other things have quit working and concentrate only on the starter motor circuit. The tool necessary are a 12v test light and a diagram. Start at the starter motor and work back toward the Battery.

The starter motor itself is difficult to access on a Ser III Jag so you can short cut by removing the large white w/red tracer wire from the starter relay on the firewall just behind the intake manifold. (The larger metal relay) Be 100% sure the trans in in Neutral and connect a small jumper wire to that white w/red tracer wire and touch it to the (+) post of the battery. The starter motor should spin. This is just a test of the starter motor circuit. If it does not spin then you need to test the battery terminals and the ground strap from the engine to the frame.

If it does start spinning you have narrowed the problem to the Relay, wiring from the relay to the ignition switch including the transmission neutral safety switch. Next step is to test the relay. It is easier to now remove the relay from the firewall so you can access each of the other wires and note the labels of each pin on the relay.

With the relay turned over so you can ID the pin numbers and see the color of the wires, test the "W-1" terminal with  the Black w/green tracer wire to see that it is a good ground with the shift lever in "neutral" or "Park". This confirms that the Neutral Safety Switch is working correctly and is going to operate the starter relay.

Next test the large plain Brown wire on the "C-2" terminal to confirm that it is powered (12v) all the time. If so continue to put you test light on the "W-2" terminal with the White w/yellow tracer wire on it for power when the ignition switch is turned to the "Start" position. If not, then the Ignition switch is the fault and you need to remove the under the dash pad and the plastic bezel on the ignition switch.

It is some work to remove the ignition switch so it is easier to unplug the wiring harness from the short switch harness and do all your testing at the plug.

You can do a preliminary test by turning the key to Ignition position and see if the idiot lights come on on the center of the instrument cluster. If not you have either lost power to the Ignition switch or the switch (or wiring) has failed.

Here are the tests for the wiring harness at the plug. Large Brown wire (12v) all the time.
Put a jumper from the large Brown wire to the White w/yellow tracer wire (with the trans in Neutral or Park) and the starter should spin. With the harness plug connected to the switch plug test the White wire for power (12v) with the key in the "IGN" position and in the "Start" position.

Now test the load Relay (power for the fuses) by by turning the key to "IGN" with the harness connected and you should have (12v) on the White w/pink tracer wire.

Some times these wires are difficult to access a bare place on the wires to do the testing so many mechanics use a straight pin pushed through the insulation of a wire to attach their test light or volt meter used for testing.

This method of testing circuits is a 100% fix rate test.

If you don't have a diagram of a circuit that you need to test, let me know and I will post one on my web site for you to use.

let me know.


---------- FOLLOW-UP ----------

QUESTION: First, thank you for your previous advice.
As I mentioned previously, the car had been starting fine until I began probing around with my fingers near the ignition looking for a day to connect the dash trim panel that covers it.
I removed that and pushed on the plug connected to the ignition switch. The car started however I could not duplicate this result on following attempts. The plug was noticeably lose. In pulling it out to check for wear the inner white plastic piece that does the turning separated from the rest of the plug ejecting the return spring and a tiny metalever of some kInd that is actuated by a smaller spring set in the plastic.
Any idea on reassembly? I notice the plug unit detaches from the main wiring harness. Should I simply replace this as a unit and forget trying to reassemble and reuse?
Thank you again,
PS want a photo of which I speak?

I have replaced those switches and as I remember the switch in a metal can had the short wiring harness attached to the electrical switch and was a part of the switch. As I remember the wires went into a plastic piece and that plastic piece was part of the electrical switch. The plastic piece with all the wires was inserted in a cup shaped metal can which should not be removed from the metal can. the metal can and all inserted into the back of the key lock assembly and was secured by one set screws in the side of the lock and tumbler assembly. The steering lock assembly was held to the steering column by two "Break Off" bolts. Thus no wrench could be used to unscrew the two bolts. We used a small sharp chisel to loosen the broke off bolts that were in a recess. The new lock assembly came with new bolts that were to be tightened until the bolt heads broke off. But you didn't have to remove the lock assembly to remove the electrical switch. All you needed to do was to remove the very small set screw in the side of the lock assembly to allow the electrical switch to slip out the rear of the assembly. But first you had to remove a plastic unit that held the fiber optics light source for the switch as it was in the way.

If your plastic piece with the wires came out of the metal can then the switch came apart. Then it would be difficult to reassemble with out another switch to look at inside. That plastic part with the wires should not come out of the sheet metal can. It sounds to me that your switch had broken and was coming apart as you touched it. Find the set screw in the side / top or bottom of the cast metal lock assembly ( I don't remember where is was located on the lock assembly) but it should be able to be felt with the plastic piece that holds the fiber optic cable out of the way.

I would not bother with that electrical switch and just purchase a new switch and discard the old one. With the new one in hand you will see how it is suppose to fit into the back of the lock assembly. So you will need to find the set screw and remove it and the can part of the old electrical switch. If the small set screw is on top it will be difficult to remove so it will be easier to take a small sharp chisel the remove the two headless bolts and remove the whole lock assembly so you can gain access to the small set screw and then remove the rest of the electrical switch and insert the new electrical switch and replace the set screw and then bolt the lock assembly in with the small chisel.



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Howard M. Fitzcharles III


Jaguar from the XK 120 to XJ-6 ser. 3 1987


Dealership line mechanic on MG, Triumph, Jaguar for 15 years, Instructor in commercial mechanics school 2 yr. Product information manager for piston and valve manufacture, Instructor & hotline answer man for import car parts importer 15 yrs.

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