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Happy new year all,

I've developed an electrical problem on my lights which blows the drivers side (Left hand drive) headlamp bulb. On checking the wiring in the lamps there are four cables on the right hand side and only three on the left hand side. What actually happens when all the 5 switch positions are activated? Up till this happened in position #1 the fender lights come on. Position #2 bright straight ahead. Position #3 beam deflected left. Position #4 ??? Position #5 right hand headlamp only. Are these the correct operations? At the moment only the right hand headlight does all functions.
Checking the left hand cables with a test lamp only 1 cable shows power. Checking with a meter the same happens but in continuity mode there seems to be two cables going to ground. Could this be the problem or is the switch a likely
candidate. I need to get this sorted before putting in the rare 3003 bulb and blowing it again.

Many thanks

Terry

Hi Terry: Can't help you with your apparent short but the first place I'd check would be wires exiting from the light switch at the base of the steering column. Per the 34 owner's manual, these are the light switch positions.

First (after OFF) operates the tail and parking lights.

Second operates the tail and tilt lights

Third operates the tail, left-hand tilt and right hand curb lights

Fourth operates the tail and bright beams.

Probably the best wiring diagram, from A.E.A., is on the PAC website under the WIRING tab in the left-hand menu.

Hi Dave,

I might have guessed it would be you that would reply. That's a good source of info I'd forgotten about. Is the switch a fairly easy item to deal with? The fault must be in that line somewhere as all the rear lights work as well as the right hand headlamp in all the switch positions listed.
Just a clarification on terminology. When you say tilt is that what we refer to as dipped, in other words, throwing the beam down out of drivers eyes coming the other way.

Hi Terry, Happy New Year!

No, Tilt is not dipping or depressed, it's sideways.

Not much experience with the switch itself, I did remove it once to repack the gear oil seal gland at the base of the column, but haven't ever actually done any service to it. Perhaps this (from the 11th series Service Letters) will help:

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Most likely the blown bulb is due to a bad ground or bad body to frame/engine ground.

How long does it take for the bulb to blow out after the lites have been turned on???? Any history of changes to the electrical or headlite system including a routine bulb change PRIOR to this problem occuring????

Dear traum...

If you notice in Owen's light position sequence the right lamp uses three separate positions, while the left uses two.

Now this translates into the following colloquialisms:

a) park, b) city, c) pass, d) drive

The novelty of this system is that the right headlight lense is cut to throw it's beam to the left, so it dips for passing oncoming cars.

On the left side bulb socket there should be a bus bar connecting two filaments thus giving two light positions with three filaments. I think if that bus bar is in the wrong position it can divide the circuit the wrong way. The original bulb sockets were labelled 1 2 3 and I can't remember which two are connected except that I would assume City (or tilt) would be the same for both lamps, and thus, the bus bar connects the two remaining filaments.

As for burning out bulbs I have been told by a well known authority that original bulbs benefit greatly from a careful application of super glue to secure the glass to the socket. If that is vibrating the bulb can be damaged.

I would also check and make sure the voltage isn't spiking from a regulator problem, and the previously ground problem that may be causing pulsation fatigue. Nothing should be rattling or vibrating in those headlights.

Hope this helps

Hi Pack V8,
Thanks for the reply. Unfortunately there has been no work done on the lighting system. I was just getting the car ready for it's annual government safety check and found the bulb blown. As you probably aware the bulbs are getting very rare and expensive, so I can't afford for anything to go wrong. I decided to check out things first with a test lamp and meter but my electrical diagnostic skills are not that brilliant and also working on old American systems with old cables. You can guess.

Now on to Tim,

Yes Tim you are spot on with the left hand bus bar. In there are three wires and when checking with the test lamp and meter in all the switch positions I only get one lead with current. With the meter I get two cables going to ground. I don't think that is correct. Can you confirm this?

Thanks everyone for your replies,

Terry

None of those posts should go directly to ground. All of the grounds in the lighting circuit (I am pretty sure) are at the lamps/sockets/housings.

Is the bus bar in good shape? Any chance you have a corrosion induced short?

Tom

Dear Traum...

Given you have an obvious harness problem, let me convey some notes I have on the socket wiring. I am 90% sure this is correct because I recorded it from a fairly pristine original headlight.

a) Draw a circle with a notch at 6 o'clock position.

b) Next draw three pins inside one at 6 o'clock, 10 o'clock, and 2 o'clock.

c) Label these 1, 2, and 3

d) The wires for the right lamp are as follows:
1: Red 2: White 3: Green

Now you can check your headlights consistent with Owen's switch diagram.

Unfortunately I don't have iron clad notes for the left side because the I never came across a pristine headlight. As well, once the right lamp is set up correctly the bus bar position is determined by matching the right side "driving" position.

However, the fact that your light still has the bar in it is a strong indication that is has never been tampered with. Many knowledgable people aren't even aware that it exists. From there you can use a test light at the switch and determine exactly what filaments are being switched on.

Hope this helps.

Hi Tom,
Are you sure about that? Both of my lamps have an earth connection. The mystery is why does one of the power leads in the left hand lamp go to ground.

thanks for your input

Terry