For a long time I have never known if my internal courtesy lights worked correctly or not. Mainly due to the fact I never or have rarely driven the car at night and never noticed if the internal lights were on or not.
Today I decided to fit LED bulbs all around the inside of the car including the courtesy lights. Had a problem with an earth on the rear left side passengers door which I have fixed and all three internal lights work. All have power and an earth.
Problem is they do not all work at the same time and I was wondering if there was a sequence that they worked at in regards to which doors were open.

With my car if;
Drivers door open the light on the drivers side "B" pillar works but none of the others.
Front passengers side door open the light on the drivers side "B" pillar works but none of the others.
Rear passengers side door open the passengers side "B" Pillar light works but none of the others.
Rear drivers side door and the the light on the drivers side "B" pillar works along with the light over the top of the rear screen. (The S Type only has one rear light over the rear screen. The Mk2 has two rear lights one on each "C" pillar. I think)

The wiring diagram for the S type which I have attached is not that clear. Purple is the main power to the lights . Purple and white is the earth which goes via the switches to ground and looking at the diagram I would assume that if one door switch it activated to earth all the lights should come on so it does not matter which door you open all the lights should be on. Am I right in that assumption?

All my door switches are working just not powering all three lights when opened, only powering one light apart from the right rear door switch which powers two including the rear screen light..

Glyn you have rewired your car completely so how do your lights work?

If I throw the map/internal light switch on the dash, first position the map light comes on and in the second position only the drivers "B" pillar light comes on.



S Type wiring diagram showing internal light circuits.

I can also add this diagram of the wiring harness route for the SType which shows that the internal lights should all be on the same circuit.



Thanks,
Confused from Torquay

 

Cass my S has no battery to check interior lIghts but I know all 3 come ON when any of the 4 doors are opened. Maybe the factory changed it by 1966?

Have you checked opening doors with the headlights switch in any ON position ? Why?
because I also know that the glovebox light and the inner boot light only come ON with the headlights switch in any of its 3 or 4 ON positions. However in my car the 3 interior lights are independent of the headlights switch, day or night.

Also was it doing this before you installed LEDs ?

 

It is the same with or without the LEDs
Head light switch makes do difference as does turning the ignition on or off as the internal lights are an always on circuit, dependent on the door switches to turn on and off by earthing out.

I am just confused as to why one light comes on when you open the drivers door, then the same light comes on when you open the front passengers door (obviously the same power circuit) but the same light plus the rear screen light come on when you open the right rear door (so should be the same power circuit for the Drivers "B" pillar light) then only the passengers side light comes on when you open the left rear door.. All lights are getting power. All lights have an earth. All lights work independently of each other (on door opening) but in reality I think all three lights should work whenever any door is opened.

I would assume all the Purple wires are on the same circuit and therefore connected to each other. I would assume all the earths are the same as in the end there is only one earth, ie the car body. So why don't they all work together.
Someone might have fiddled in the past and put in a separate power circuit to one or two of the internal lights so when a particular door switch is earthed it is not earthing the whole power circuit going to the another lights. My next thought is to isolate the correct power circuit at the fuse box and then see if any of the lights are still powered. That should show me if there is a separate power circuit been installed. Might even be as simple as two power circuits but running from a separate fuse and therefor not joined together. More investigation tomorrow.

 

Looking at the circuit diagram, the P cable is permanently live and goes to all the lights. On their ground side, all the lights are connected to the PY cables which should be electrically continuous. Anything that grounds the PY cable turns the lights on. The panel switch and any of the door switches should turn everything on. The diagram shows some bridging wires. If one of those is missing, breaking the PY line, then the switches might operate only some of the lights, but that shouldn't cause what you're seeing. Still, I'd be tempted to start be checking if there's continuity of the PY cables between all the switches and lights. It may be that two PY wires meet at a switch with a poor/intermittent connection that comes together when the switch closes.

 

again, all I know is that in my S type all 3 interior lights come ON whenever any door is opened.
Something must have been mis-connected when you restored your car.

 

Thanks Pete I will do some more tests tomorrow on the continuity of the earths and on where the live feeds come from. The more I think about it the more confused I am as what is happening should not really be possible.
As for connecting things back together Jose after the rebuild all the wiring is original and most of it was not removed from the car just pulled to one side but obviously something is not right. It is only minor but frustrating.

 

Cass all the interior lights should come ON when you open ANY door. That's why they are called "Courtesy Lights". Same thing in my XJ-6, they all come ON.
Must be a crossed wire where they were disconnected and reconnected. Retrace the steps, check each lamp wire connections.

 

Open any door and all three lights come on. LEDs can cause all sorts of problems. With Benz you require to insert a shunt resistor and the LED. i.e. a resistor in series with the LED. I replaced every door switch.

If you get the correct festoon lamp LEDs the resistor should be built in. Otherwise the value is 22 Ohms. Yes the Benz is a far more "electronic" car than ours but we are still moving from incandescent to high intensity LED. I've kept my car incandescent & have plenty of spare lamps.

 

When I turn on the dash switch for the internal lights again only the one on the right side Drivers "B" pillar comes on even though they all have power and earth and light up individually so I am sure that there must be two sources of power going to the lights. I will check the fuse blocks behind the dash in the morning to see if I have two purple wires going out live from different fuse blocks. Might be as there is a left and right wiring loom that they have been plugged into different fuse blocks so the lives are not connected.
I will update tomorrow.

 

An LED like many other electric components can either take too much current and burn out or too little such that something else in the circuit doesn't work. Presumably these LEDs are 12 V automotive so don't take too much current. If they did, they could be protected by a series resistor, but shouldn't cause the present problem. Taking too little current commonly happens when they are used in indicator lights; they don't take enough current to heat up a conventional flasher unit so either stay illuminated or flash very slowly. In that situation, a resistor of similar value to the original bulb can be connected in parallel LED to draw more current so everything works. I'm not sure if this is relevant to Cass's interior lights. I guess it's just possible the LEDs don't take enough current to break down a dry corroded connection. Still, it brings us back to poor connections.

I have a distant memory of one of the door switches on my Mk2 becoming reluctant to operate, mainly due to not closing well. A spray with some machine oil and a dab of grease seemed to put it right. Warning: persons, particularly of a female persuasion who self invite themselves into your car, seem to have a magnetism between any grease around a car door and their clothing and it's never their own fault.

 

Refresh page for my edit.

 

I have just checked my MK2 and all of the 4 lights (2 in B pillar and 2 in C pillar) come on when any door is opened. At least they do now once I replaced a blown bulb in the LH B pillar.
So, the logic is correct for the MK2 and S type to have all lights come on whenever any door is opened. So, Cass's assumption is correct.
With power proven to be at all of the lights it basically comes down to the earth switching wiring.
I think I would start with the LH front B pillar light and trace the earth wiring for that as it appears to be non-operative..

 

OK foolish mistake as I left the side lights on over night and turned up to a flat battery. Duh!!!!!
Anyway whilst the battery is charging I checked the continuity between each light (purple wire) back to the fuse 7 terminal and to one of the four purple wires connected there. All lights are connected to the same terminal wire. This means all the lights are getting power from the same source.
With this it can only then be that the earth wires (Purple and Yellow) from the lights are grounding individually not collectively. So if individually when one door opens the switch grounds out and a light comes on but all three should come on.
I am going to have to chase the earths now as it appears that the two front door switches plus the right rear door are all earthed together as these all work the right "B" pillar light. The rear left door earths the rear window light and the left passengers side "B" pillar light.
Back to work to take all the switches out.

 

So I have chased the earths and it appears the earth to the rear left door is not attached to the front passengers switch wire or has a break. It is difficult to chase the earth to the break as the wiring loom seems to run in to the left side of the engine compartment and although I found the Purple/yellow earth wire I cannot see where or how it should connect to the earth wire that comes from the front door switch which appears to run under the dash to the interior light switch. So if in doubt put a new wire in. I jumped a wire from the purple/yellow earth from the rear passengers door and connected it to the front passengers door switch earth wire and hey presto all the lights now work together for all the doors and the dash interior light switch.
The wiring is pretty easy when you think about it but chasing wires in an old wiring loom is not easy. Nothing to do with swapping to LEDs or incompetence on my behalf for not wiring it back up properly I think.

 

i take it you know that solid state devices, like LEDs CAN be polarity sensitive? emphasis on CAN. although it seems that more and more of them are polarity neutral these days.

and ya, courtesy lights are like the three musketeers, "One for All and All for One!".

if i was having this problem, i'd be digging around in my trash, looking for my old incandescent bulbs (which i would have probably thrown away) and see if THEY work.

tangentially....in a recent switch to LEDs in my 1953 MGTD's dash, i found that the "dimmer" fails to dim, whereas in the past it functioned as expected. the more i thought about it, i decided that with the trivial amount of current the LEDs draw, that they get all the current they need with the "dimmer" on its lowest setting. ergo...no dimmer, more or less.

 

You get dimmable & non dimmerable LEDs.

 

...figures... *sigh*

reminds me of a story from a few decades ago. ...i was suffering from an inner-ear infection when and old high school friend came over and offered to drive me to the emergency room at a nearby hospital. i was suffering terribly from motion sickness as a result of the infection and proceeded to vomit out the window of his car several times on the way. he waited patiently at the hospital while i was treated, and on the way home he asked me what the doctor had done and i tossed him the vial of tablets the doctor prescribed. he took one look and tossed them back, with the observation, "...figures...you're dizzy so they give you dizzy pills".

 

These LEDs I fitted were polarized and had a red dot on the positive side so they could be used for positive or negative earthed cars you just had to turn them around to fit. Problem with that is you only get one chance to get it right or you blow the LED so you have to confirm, with a meter, which side is which in the light fitting first.
I only had one old incandescent bulb which worked which is why I decided to fit new ones and thought of going down the LED route. Five years ago when I changed some other internal lights over to LED they did not make an LED to fit the courtesy lights.

 

The alternative is that you might have to hide some circuitry at your dimmer switch.