1982 KZ1000J electrical problem

Hi Claude 
Grab a voltmeter and a wiring diagram and ensure you carry out all test with everything connected and the system turned on (you will need to go into the back of the connectors with your voltmeter) the problem will be easiest to find when the fault is present
•    Measure the battery voltage ( reference voltage) you will have to keep checking this if the process takes a while as the battery will go down during testing
•    Measure the voltage at the component that isn’t working and compare to the battery voltage (there should be no more than approx 0.5v difference)
•    Now follow the wiring diagram and work back from the component towards the battery checking the voltage at each point
•    You should get to a point where you can identify between which two points you are losing voltage
•    If it is a component such as the ignition switch you will see a difference between the input and output voltages at the switch connector (before you replace the component check the connections are good to it)
•    If the fault is in a section of wiring you will need to visually inspect the wire (sometimes if the insulation is damaged water gets in and corrodes the wire, in this case you would normally see green powder on the wire)
•    If the wiring is the fault you will need to cut out the corroded section and replace (make sure you cut it far enough back to get to clean copper (this can be several inches as the water capillaries up the wire)
Happy hunting

OK, the bike is now on the work table with fuel tank and seat removed and the hunt is ready to begin.

However, there's one strange thing, opposite to what I always tought about 12V DC voltage. I always tought that the 12+ power is "circulating" from one end of the wire, feeding the components which uses the power and "dissipates" it through their respective ground.
When looking at the brown wire, it is fed with 12+ at BOTH ends. Front end is fed with ignition switch's white wire and rear end is fed with fuse box's White/Black wire (also coming from ignition switch).
I'm thinking that I could cut the brown wire about anywhere and that any "accessory" would still get its 12+ power anyway by the end it is still connected to.
What am I missing???

This being said, first thing I saw is that there is a voltage drop at the ignition switch. Battery is 12.5V and brown wire is getting 11.7V (at both ends). Is this acceptable?

Well, I checked the voltage of all the components (via their respective connectors) connected to the brown wire and they all are at about 11.8 volts with a battery reading about 12.5. I’m kind of perplex about what to do next.
I can’t take measurements when the problem is present as it is an intermittent one.
All I did was to replace all the fuses with new ones even if the old ones seemed to be OK.

Hi Claude - 11.8v is not OK, good news you now know you have a resistance fault. The ign switch wiring is as follows
White - main feed in
White/black - main feed out to fuse box ( feeds Brown, Blue & Red/White)
Brown - feed INTO ignition switch for engine kill switch
Yellow/Red - feed to engine kill switch
Red -parking lights
Orange/Green - feed to indicator switch
Orange - feed INTO ignition switch for indicators
The ignition switch is 5 switches in one
"ON" position
White switches to White/Black
Orange switches to Orange/Green
Brown switches to Yellow/Red
"PARK" position
White switches to Red for parking lights
Orange switches to Orange/Green for emergency lights

Check voltage at White/Black at the fuse box (it feed Brown, Blue & Red/White) is it battery voltage
YES - the fuse box is faulty (remember it's 40 years old so even if the contacts are clean they loose spring tension with age)
NO - check voltage on White/Black at ignition switch, is it battery voltage
YES - the fault is in the White/Black wire between the ignition switch and fusebox
NO - check the voltage on the White wire at the ignition switch, is it battery voltage
YES - the ignition switch is faulty
NO - check the voltage at the main 30a fuse, is it battery voltage ( there is only the red wire back to the battery to check if the voltage is still low at the main fuse)

This should only take about 15 minutes to check (REMEMBER TO CONNECT THE NEGATIVE SIDE OF YOUR VOLTMETER TO THE BATTERY NEGATIVE TERMINAL FOR THESE TESTS)

Happy hunting

Also, the power does not just dissipate, it returns to the battery through the negative cable. Yes, some of the energy is converted to heat along the way, and that gets dissipated.

Wookie, many thanks for your prompt answer; it is very helpful and, believe me, extremely appreciated!
I just took some measurements. Trying to be as clear as possible, I made the joined picture and the written numbers vs voltage do refer to those on the picture. In case it could matter, I took the measurements directly on the RH end cap of each fuse.
I want also write that I do have one more switch and fuse box (from another J model) and I also used those components. So, by mixing both switches and fuse boxes, I made four tests which all showed about the same results. Without any surprise, #1, #2 and #3 all got the same measure.
1- 12.16V
2- 12.16V
3- 12.16V
4- 12.50V
5- 12.40V
Battery voltage: 12.54V
White wire (at switch): 12.29V
White"Black wire (at switch): 12.23V

Once again, I'm kind of perplex as all is not "good" or "bad". Looks like there always is small voltage drop the farther away the measure is from the battery. But the 0.34 volt drop between #4 (white) and white/black (#1, 2, 3) does not look to be correct.

What do you think? What should I do next? 

Hi Claude, so

Between the battery and the ignition switch you are losing 0.25v
Through the switch you are losing 0.06v (switch is good)
From the switch to the fuse box you are losing 0.07v
These are all OK especially given the age of the wiring (as a guide both VW and Jaguar spec up to 0.5v loss as acceptable on a modern vehicle although the wires are a lot longer)
Is the output voltage from the fuse on the brown wire still 11.8v (losing 0.36v through the fuse would still suggest a problem here as there should be no loss over such a short distance )
May be worth looking at the connector where the Brown wire joins the fuse box (is the voltage different to a reading taken from the fuse holder at the front)

Let me know how you get on 

Wookie, I just checked the voltage on the brown wire of three components it is feeding and it is the same than #1, 2 and 3 (12.16V).
At the fuse box connector, brown wire also reads 12.16V.
Any other other clue please?

Ok Claude this is not uncommon,
12.16v as an end voltage is ok, however this has increased from 11.7v on the brown wire when you started so you have picked up 0.46v from the work you have done. The most likely reason for this is unplugging and reconnecting the wires to the components you have swapped out has scraped the connections clean and are now making a better contact. You might see some marginal gains from cleaning and tightening (or replacing) the connectors you have been working on but.
I would be inclined to " suck it and see" you may have rectified the problem by accident (for now at least) or alternatively you would need to test it when the fault is present at which point the test results would be more conclusive.
The readings you are getting don't warrant further investigation, as a last resort you could connect your voltmeter to the brown wire and manually manipulate and pull the wiring in the areas tested and see if the reading fluctuates. Other than that there is little more you can do without a fault to diagnose. Hope this helps ( electrics are the devils work, especially on older vehicles !!) logic will usually prevail

Wookie, when I made all those tests yesterday, I had an intelligent battery charger connected. I was checking battery voltage at each step to be sure it was consistent (and it was). Final voltage on brown wire was 12.16V
The prior day, when I got 11.7V on the brown wires, there was no battery charger connected so the numbers surely can't be compared.

I assembled back my 1000J today, and it is ready for a "road test".
I put the switch connector outside the headlight shell so any voltage reading on the side of the road will be quite fast to do if the problem still appears. I did not fit back the side covers either so the connectors will be readily available. I also taped under the seat a photocopy of the fusebox picture I posted so I'll know where to measure if needed.

Because the problem is intermittent, I have to act like this. I truly hope the problem is gone but I really would like to know what is (was?) the cause.
Many thanks again for your time and comments!!

NOTE: I also had the switch connector outside the headlamp shell the last time I got the problem on the road. I was carrying the other ignition switch I have at home and I have been able to swap them pretty fast. The problem was still present so I believe the ignition switch is not the cause.

Claude I think the approach you are taking is the right way to go, you could spend hours driving yourself mad looking for a fault that's not there. If the fault does re-occur check if the lights are still working (if they are this will iliminate everything up to the fuse box as they are fed by the same White/Black ignition live as the other fuses) this will only really leave the connection for the Brown wire at the back of the fuse box. If it's not fixed I think you are really close to a solution now, just stay logical in your  approach and you will be fine

Hi Claude, I was wondering how you have been getting on with the gremlins in your "J" ?