Hello experts, I’m having an issue with my turn-signal and I’m not sure how to diagnose the problem. The turn signals work correctly on the outside of the car but in the cabin, the left and right lights stay on constantly while the car is running and when the turn signal is on, the standard clicking noise has been replaced with a continuous buzz. I replaced a cylinder looking electrical component under the dash that seemed to be making the buzzing noise but the problem still persists. Any troubleshooting steps would be greatly appreciated.
New issue, or has it always been like that?
The cylindrical film-can things are relays, alright. A buzzing noise can develop with a bad contact, just like an old bell; whenever the relay clicks the bad wiring goes open circuit for a split second, and so on. But the indicating lamps must be miswired. My guess is they go to the input spades of the flasher unit instead of the output side. I don’t know if the hazards are seperate but what happens when you use them?
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Troubleshooting rules 101 is never trust anyone, not even yourself. Start at the easiest things. Find out what works and what doesn’t, and then simply cure the fault 
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Both in ‘left’ and ‘right’ turn, Adam - and what happens in ‘Hazard’ setting…? And what happens if you turn the park/headlights ‘on’…?
The usual incorrect behaviour of the inside repeaters is caused by failed diodes in the circuit. They prevent cross feeding power to the internal bulbs from the external circuit. However, if the external bulbs flash (front and back) at the usual rate; the relay is delivering intermittent power, as it should. The buzzing, instead of clicking, indicates that the relay does not work - very puzzling…
Have you done any work behind the instruments where the bulbs are connected, ref David’s remark?
A further step is to locate the source of the buzz; ‘that seemed to come from’ the component you changed. That the warning lamps are constantly lit (no variations) while all the external lamps works correctly is ‘impossible’ if the wiring is correct…?
Frank
xj6 85 Sov Europe (UK/NZ)
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I have nothing to offer this topic because I’ve got a series III that does just the opposite. neither lights aluminate in the car (except the bulb light). both indicators on the instrument panel don’t work. but the bulbs on the outside work (now) the flashers also work. With a project list the size of an unabridged dictionary. It’s not on the top of my list.
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When you get around to it, Mark - check bulbs…
Blocking diodes are used to prevent the ‘wrong’ warning lamp to light up - the ‘correct’ lamp is powered from the relay and grounded through the unused outside bulb. It is a bit intricate to tackle without time to spare…
Frank
xj6 85 sov Europe (UK/NZ)
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I consider myself reasonably adept at automotive electrics but operation of the Jaguar turn signal circuit is one of those things I have trouble wrapping my head around. Fortunately for me I’ve never had a failure requiring anything more than a flasher relay replacement
Cheers
DD
Adam,
I’m a bit confused - not unusual.
Your profile indicates that you have an 1986 s3 VDP. So do I. When I did my LED conversion, I went all through the turn signal circuit. I am confused as to what the “cylinder looking component” is. The DAC1731 flasher is black & square, as are all compatible aftermarket flashers that I know of (yes, I did a survey). The original DAC1731 is marked “Hella TB44” on the top.
Starting at the most basic step, does the turn signal operate correctly when the ignition switch is in the I-position, ie accessory?
Ron
You have three different “modes” of operation and three different “sets” of lights, with various combinations, all with just one relay.
Today they would call it a flasher Module.
A brilliantly intricate design indeed.
Aristides
Adam,
I had a similar issue recently with the directional signals in my 1990 V12 Vanden Plas. When I turned on the directional signals, all of the lights on the exterior of the car worked properly, however on the inside of the car the directional signal indicator lights on the dash would only flash once or twice and then stop. I could hear the flasher unit clicking as it should, and the exterior lights continued to flash appropriately, but after a flash or two the dash indicator lights in the speedometer and tachometer would not flash. I removed and replaced the Directional Indicator Flasher Unit (DAC1731) with one from one of my parts cars and that fixed the problem. The Flasher Unit is rectangular in shape, has a black plastic cover, and is located inside the dashboard on the driver’s side.
The cylinder shaped component you replaced could have been a variety of things including the black Lucas Load Relay (DAC1027) or possibly an aftermarket part installed by a prior owner. Can you provide more details or a picture of what you replaced?
Paul
I’ll be home in a few days to do some more R&D on the dash indicators. The problem started when my alternator died. I was driving, and the turn signal indicators quit working. When I looked at the dash gauges, I noticed the voltage was low and then the car died. The indicators haven’t worked since then.
@Ron_Knipper - I love the idea of converting to LED as all of the interior/dash lights are terrible. Do you have a write-up of the LED conversion you can share?
Thank you Frank, this makes sense. because the outside bulb was “backwards” with the parking lights on, indicator would blink, backwards. Instead of light going completely out then back on in a “blinking cycle” it just got brighter. I fiddled with the connector inside giving it a bit of a twist, I got the light outside to blink properly, but now the inside indicator lights don’t blink at all. I also tried an LED bulb rather than a traditional 1157 bulb.
but that is for another day.
Thank you again Frank
Mark
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As long as the ‘outsides’ work, Mark - it’s a good start. But turn signals differing from driver intentions due to lack of feedback is a bit iffy…
The warning lamps are fed on a separate circuit from the flasher unit, powered in step with the outside bulbs. Ground is provided by the ‘unused’ outside indicator lamps, but both power and ground are required for any bulb to light up - and working bulbs, of course…
As a general aside; when dual filament bulbs are used; a short between filaments gives bewildering symptoms. However, what is a ‘backwards’ outside bulb…
Frank
xj6 85 Sov Europe (UK/NZ)
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the short filament is the one for the parking lights. and the big filament is for the indicator. When I connected the replacement bulb. The bulb aluminates “backwards” the little filament was the indicator while the big one was the parking light. when the parking lights were on, the little filament is what blinked for a turn indicator. that’s a backwards “bulb” 
I took a screw driver and repositioned the connections in the bottom of the socket so they aligned properly. Some how the connections got twisted around.
Adam,
Certainly, your first priority is to insure the electrical feed is working properly, and then you can troubleshoot the the turn signal. I still strongly suggest determining if the turn signal works correctly with the engine off as the first step.
I do not have a single written description for LED conversion. I did it in stages. An important step is to decide what dash illumination you desire. There are many JL posts on the topic. Effects vary greatly eg brightness, color, special effects, etc. In many cases, it can be as simple as choosing the right LED bulb. Other aspects are more involved: turn signal with LED external lamps, bypassing bulb failure monitors, PWM dash dimmer, 12V heated screen indicator, and (by far the most complex) eliminating the dreaded Opticell. I have scattered information on what I did and will be happy to post it on specific topics.
Back on topic… Here are some notes I did a while back on the turn signal. The factor schematic is a bit convoluted; this illustrates operation a little clearer.
Ron
Frank,
Back to me; If you ask my wife she’ll tell you it’s always about me! I have no idea what she’s talking about. 
I’m wondering if my interior indicator bulb illumination issue is a defective flasher unit. if I switch on the flashers there’s no flashing going on. Of any sort - lights or trench coat. But my indicators do work outside the car? Weird? or do I not understand?
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Which means that part of the flasher unit is working, Mark…
At the flasher unit; light green/blue wire delivers ‘pulsed’ outside power - light green/brown deliver ‘pulsed’ power to the interior bulbs.
First test is to check power on light green/brown wires with the outside lamps working. if not; change the unit. A counter check; with the stalk switch in neutral - disconnect this wire, or remove flasher unit, and apply power to the wire. In theory; both internal lamp should light up…
Just for a start…
Frank
xj6 85 Sov Europe (UK/NZ)
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Thank you again Frank, as always, you’re brilliant! I’ll give it a go this weekend.
Thanx
mark