Jaguar Repair/wiring


QUESTION: I hope I am not sending this twice.Do not asked me for code or show receipt so here I go again.
Fuse one is powered by head lite switch,fuse2 by dipper lite switch and fuse 3 and 4 by just turning on ignition switch to on position. Think I have that right. But real question is fuse 5 , do u have to turn on side lite switch to get the panel lite switch to work? Or do I have the wiring wrong? Fuse 6 by tuning on ignition switch and fuse7 and 8 all the time? Not sure about 6,7,8 please help me out with that part.

 Next I am rewiring my dash and my lite has never turn on when I open the doors and I what them to work, does the map lite turn on when u open the doors or the over head dome lite turn on. The wires are p/w some as the wires on my map lite, my map lite  has power to it and works when I turn the switch on but nothing goes on when I open the doors , I have run the new wires to the door switches , I don't think I have power to the door switches,and will check that today. These are my goals for the week end and would be a great birthday present to myself
Mike   Thanks again for the help

ANSWER: Mike, When working for several different brands of cars in dealerships I learned to pick one circuit to correct and after I had that one circuit corrected then I could proceed to another circuit.

You seem to have several issues so you need to concentrate on only one circuit at a time. To try to cover several at the same time I would need to write a book on the electrical system and we don't have room in this program to do that, so lets correct one circuit at a time. When we get one circuit complete then move to another circuit.

I take it that you don't have a wiring digram of your car. As I remember you said your car is a 4.2 E-Type ?? I am going to post a diagram on my web site for you to copy and so you can follow what I cover on each circuit. Go to, so you can follow what I talk about.

First we will cover fuse #5. (lower left quarter of the diagram) As you can see the #5 fuse don't have anythng to do with turn signals. That is on Fuse #7 (upper right quarter of the diagram)

Some mechanics start at the source (power supply) but I found it easier and quicker to start at the load (item that don't operate) and with a 12v test light follow the trail, testing at each joint until you get to the battery supply. This, I found is a 100% fix rate on any electrical problem on any brand of car. But ONLY look at ONE circuit at a time. Never try to diagnose by symptoms, only by testing !!!

I learned early to listen to a customer and smile and nod my head as he or she spoke. Then when they left I eraced everything they told me other then what didn't operate and went testing as I would do anyway. Symptoms will often lead you down a wrong rosd and waste time. But I found that if I told the customer all the odd symptoms were useless information, it often hurt their feelings so thus the "Smile and nod of the head".

1. Never touch an electrical problem on a car without a diagram.
2. Only pick ONE circuit to work on at a time.
3. Start at the load (item that don't operate) and test with a 12v test light and head toward the battery following your diagram.

This procedure has a 100% fix rate. Follow this procedure and it is impossible to fail.

Let me know the results of the first set of tests and we will go to the next set.


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

QUESTION: Howard I am sorry I don' understand the answer. I didn't ask anything about turn signals. Thank u for the diagram,I do have one. My question is do u have to turn on the SIDE LITE switch to get power to fuse5.
I was able to get my map lite to turn on when I open the doors first time in 32 years.
BY doing every thing that u said about following the diagram and  following the load with a 12v test lite follow the trail. That is way I bought the 12v test lite like u said. I try very hard to listen and do exactly what u say.
 I am not able to tell buy reading the diagram if the side lite switch gets power to fuse5. ALL I NO RIGHT now is that when I turn on the SIDE LITE switch I get power to fuse5 and they my panel lite switch when turned on lite my edge lite.
SO how does fuse 5 get power???

 After fixing my door lite, I went on to my horns, using the diagram and the 12v test lite I followed the trail and tested the wires one at a time. I checked to see if I had power coming out of the green wire that goes to w1of the horn relay coming off fuse 6 and I do. Next I checked to see if I had power coming out of n/p to w2 of the horn relay coming off of     fuse 3 and yes I did.
 Next I checked to see if c1 p/y has power coming off the terminal  running to the horn and if w1 p/b has power coming off the terminal running to the flasher unit and NEITHER one did. I would think the p/y wire to the horn would have power but I am not sure. Would u be able to tell me if c1 p/y running to horns and w1 that runs to the horn push button that runs up the  flasher unit should have power coming off the terminals.If they should , does that mean the relay is bad. I also checked to make sure that all the wires were on the horns and they were.
 Thank u again and I do try to listen to every thing u say!!!!!!!

Yes, the two light switches in the center of the switch panel do power up Fuse #5.

The horn button does not power the relay, it grouds the electromagnet in the horn relay to make the relay connect the power to the horns.

When you push the horn button you ground the Purple w/black tracer wire that is on W-2 terminal on the horn relay. This makes the magnet in the relay pull the contacts together. The magnet is powered by a Green wire from fuse #6 which is powered when the key is "ON".
The horns are connected to C-1 terminal on the horn relay by a Purple w/Yellow tracer wire. The power for the C-2 to C-1 contacts inside comes in on C-2 terminal by a Brown w/Purple tracer wire from fuse #3 that is hot all the time.

Most of the old British Lucas relays were labled with those same terminals. Later German and Japanese relays were numbered 85 and 86 for the magnet and 30/51 and 87 for the two contacts. Also, Lucas wiring was very uniform in their color codes for all British cars. For example,
Brown wires are power sources usually unfused. Red wires were mostly for small lights anywhere on the car. Green were usually acessary wires of some kind. Black wires are grounds. Blue wires were headlight wires, White wires had something to do with ignition. Purple wires were power wires usually unfused. And usually horns.
Even the tracers on the wires are usually consistent. Blue is for a head light but Blue w/White tracer is a High Beam head light and Blue w/Red tracer is a low beam head light. A Green wire is usually an accesary and a Green w/Black tracer is a ground for an accessary.

This is not 100% on all British cars but close to it. It makes it easier to do electrical work.


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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.

Associate member SAE EAA member

Import Car magazine

ASE Master Auto with L-1 certification up to 2000

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