Since I am taking this opportunity to try to get everything working as it is meant to I am now trying to correct the wiring for the overdrive indicator. It is meant to dim when the lights are on and it does not.
I have the wiring diagram and I can see the Red/Black should be the feed for the indicator light and the Yellow/Purple comes from the overdrive solenoid.
I have a new light switch so I have removed the resistor from the old switch and fitted it to the new.
Does anyone have a foto of the light switch connection for a MOD. I have found one for an automatic but I would like to be sure.

It s a bit strange (as usual although its often just me!). The black wire going to the light is no longer connected to earth so I guess something came loose when I re-assembled the dash, I can always provide a new earth.
I was expecting the Red/Black wire I find on the light switch to be connected to the red wire of the indicator light, it is not instead the Yellow/Purple seems to be in direct connection to the light. Either I am making a thinking fault or someone (not for the first time) has taken a shortcut with the wiring.

Anyway if someone could send me a photo of the back of the light switch on an MOD I would be very grateful.

Update:
As I suspected someone has made a modification. I disconnect both the Reb/Black and the Yellow/Purple and the indicator lamp still works fine!
I guess I will have to remove the centre console now to get to the source.

 

https://forums.jag-lovers.com/t/jagu...tmare/371350/3

The pictures at post no. 3 in the link may help. The colours of the wires are cleaner than those in my car.

 

Thanks. In some ways I got lucky. I put everything together for a test drive. After a few corners I noticed a steering problem so I stopped. Somehow the indicator warning lights/over drive light wires got caught on the self cancelling indicator mechanism and most of the wires got ripped out. Needless to say I was not a happy camper as I now needed to remove at least the rev counter to repair the wiring. With the rev counter removed I could see the red/black connector was not connected and the bypass someone had decided to make. So it has cost me a little work but now all is wired correctly!

 

Too often, the greatest challenge with an old car is the result of previous repairs and restoration.

 

all swell that end swell.

 

So I got a new wiring loom for the indicator and overdrive lights on the steering column. Took out the old loom and plugged in the new. Took photo’s of everything to make sure I connected it the right way. Now none of the lights work so I grab my multimeter but it took me a while to realise that my car has been converted to negative earth. So now all the negative connections (black wires) should carry 12 volts and the coloured should be earth or floating if switched off? But the earth connections are connected to the body/chassis which is connected to the negative side of the battery. I know I must be making a simple thinking error (denk fout). Could someone put me straight. I feel very silly asking this as I have been working with electricity all my life!

 

The wiring loom for lights remains exactly the same after swapping polarity. The bulbs aren't sensitive to the direction of current flow. Think in terms of live and ground and everything is the same (apart from the sign on your multi-meter).

 

Thanks. That’s what I thought. I am afraid the previous owner has done something strange again. Although I really don’t understand why the indicator warning lights don’t work as they worked before. Something must be loose. Anyway back with fresh eyes and a fresh brain tomorrow.

 

With this kind of electrical problem, most often it's necessary to trace carefully through the wiring, checking for continuity by measuring resistance or voltage.

 

I have been following advice and tracing carefully through the wiring.
The indicator wiring all makes sense and I can trace the wires back to the flasher unit and the steering column switch, but still no joy!
The red and red/black overdrive indicator wiring all makes sense except that the black "earth" cable is not earth but is connected to the unidentified wire emerging with map light wires.



Someone has put a fuse in the wiring for the Overdrive switch!





I am finding multiple black wires that are disconnected.


My conclusion is that there has been a problem in the past and this has been solved by disconnecting earth wires and then putting in a fuse when it goes wrong.

Update:
I have been doing a little more reading and it seems that a fuse in the overdrive circuit is a standard part?

 

The solenoid has an internal switch so that it takes less current after it has moved into the hold position. If it sticks trying to open, it takes a continuous high current and can burn out. Someone may have added a slow blow fuse to protect the solenoid.

 

Interesting. As I have been testing sometimes I see a very high discharge and have to quickly disconnect the battery.

 

Oh my the issues and unknowns with old car wiring. I'm not sure even the almighty could tell one what "undocumented " changes have been made over the decades to our old cars.

I don't mean to hi-jack this thread but I too was recently faced with multiple wiring issues on our 1960 MK2 2.4 that has a transplanted 3.8. The wiring was so hacked up it was impossible to trace a circuit and compounded by the total discoloration of the wire insulation. Every wire was a dirty brown and some of the connections were badly corroded. I was very afraid of at some point a fire. The factory wiring diagram was a great help, but of course did not reflect the many hack changes.

SO, we bit the bullet and purchased a new wiring harness. Got a great deal on a harness for a MK2 auto transmission harness at 50% off in a close out sale. Our car is a 4 speed OD so we knew there would be differences. But as it turns out not many. Well worth the price. We just completed the removal of the old harness, with the engine in the car, and installed the new one. During the process we upgraded to an alternator and are installing A/C as well. In addition we installed a modern fuse box. I chose this one.

https://classic-technologies.com/

The fuse box may have been an overkill, but now each major circuit is fused and relays transmit the high current requirement circuits.

So far so good, car is running, no fires from burned up wires. So now I know exactly the wiring of my car. It was definitely challenging and falls into the saying "don't try this at home". But at the end of the day I think it wall be worth it. Now have to finish the A/C hose routing.

I'll try to post photos when totally done.

jjsandsms

 

Got it. Well two things really.

First why didn't my interior indicator lights work. After having exhausted all possibilities the only thing remaining was the flasher unit itself. The flasher has 2 relays one for the actual indicators and one for the interior indicator lights. With the wisdom of hindsight I should have noticed this earlier. Anyway from the photo you can see the connecting wire for the interior flasher lights has melted!



So that's solved. Now why won't my overdrive indicator dim when I switch the lights on.
Please feel free to correct my thoughts here.

The overdrive light is 2W. P=VI so with a 12V system the current must be 2/12= 167mA.
On my light switch I have a very nice resistor that fits onto the switch (the flat disk type). I have measured this resistor and it is 2.2 K ohm.
So if V=IR then 0.167*2200=366V. This would explain why I see 0V when the resistance is in the circuit.
I don't know what the ideal voltage drop would be across the bulb.
Looking at photo's of switches I see 150 ohm resistors being used.
so 0.167+150=25V which is far too much still.
I would think a 4V drop would be good. So 4/0.167= 24ohm.

Is this correct thinking? I really don't understand why I have such a nice resistor that is obviously specially made for the switch with such a high (incorrect?) value.

Can anyone shed any light?

 

If the lamp is rated as 2W when supplied with 12V, the resistance of the lamp is 72 Ohms under load. Put a resistor in series and you have a voltage divider. So with a 72 Ohms in series with the 72 Ohm lamp, there will be half of 12V across the lamp. That's 6V and the power dissipated in the lamp is a quarter (i.e. a quarter of 2 Watts is half a Watt). In fact, it's a bit more complicated as the resistance of the incandescent coil changes with temperature and perceived brightness is another matter. My suggestion is try something in the range 30 to 60 Ohms and see how you like it. Buy a bag of 22 Ohm 2 Watt resistors and mix them in series (or parallel) to achieve your target brightness.

Of course, the obvious question is: since you have everything open and dismantled, why not replace the bulb with a LED? You could arrange to have say two LEDs for normal illumination and one for the dimmed setting or buy a dimmable LED.

 

Thanks Peter, very clear. I have replaced all the illumination bulbs with LED’s. I found all the others bright enough.

 

So I repaired the flasher (I do love old tech) and got myself a bunch of resistors.

Now I can do the reassembly.