So I am still trying to sort out why my green turn signal dash lights don't work. All exterior indicators work normally, and the relay clicks away, but these dash units don't. If I used led's for the exterior indicator bulbs, would that have messed up the system? I've replaced the "original relay with a generic one and the problem remains the same. And where are these mysterious Diodes located? I can try replacing those if I can find them.
Ian

 

I'm having the same problem, Ian. Looking for suggestions too.

Dave

 

Do your indicators work when using the hazard switch? It's all connected. They both should illuminate at the same time. I highly suspect the diodes are in the tachometer and speedo housing and it may be worth the trouble to move them to a spot under the dash easier to reach. It doesn't look like leds should interfere but I didn't dig too deep in the Haynes manual diagram. Problem may be the bulbs themselves rather than the diodes. Pull a bulb and measure for continuity.

 

one of the famous diodes is in the harness that has all the wire and bulb connections going to the tachometer. In my car the tachometer is the left gage with the strange behaving left signal indicator.
You need to peel the tape back around 3 inches to find it.
I replaced it and it made no difference, it keeps acting strange. Don't waste your time.
It's not the Diode.

I blame the turn signals Switch.

What happens in my car is that the left arrow turn indicator flashes 3 or 4 times and then stops flashing, but outside the car everything is normal.
I notice the bulb loses intensity or voltage to almost zero. I gave up.

 

Jose, that's exactly what mine used to do. Blink a few times then go dark. Everything outside is normal! Going to hook up an led. Perhaps it's a age related poor connection to the bulbs or just tired bulbs. Will report. Ian

 

I had the same problem ages ago on my first Ser III. It was the flasher.

I'm a little suspicious of "generic" in this case. What brand and part number was it? Did the terminal markings match the original exactly?

Cheers
DD

 

Doug, the replacement flasher is a Moss Motors - Jag p/n DAC1731 with URO Parts branding. 4 pin and perfect fit. It behaved just like the "original" one, ie. no dash lights. I think it is generic as somewhere on the WWW I saw a review from Australia pointing out that the 4th. pin is for powering "trailer" indicators, but is used on the Jags to power the dash indicator lights. I dont understand how that would work to operate either the l/h or r/h dash lights. Points back to the selector switch and/or those mystery diodes. Still digging. Ian

 

Ian, does it happen only at the Left (tachometer) side Turn Signal indicator ??

Doug, I have replaced the flasher relay several times and it still does it.

 

Um, just musing here, but someone mentioned replacing the bulbs with LEDs.
If that's the case, the Flasher must ALSO be an LED friendly unit.
Because, ancient OEM flashers worked by total bulb current heating an internal bi-metal strip on the points, which then get hot enough to trip the internal spring thingy and separating the points, which started the process all over until the lever is centered.
The Clicking sound is the action of points breaking and reconnecting.

As LEDs draw so much less current, OEM style flasher units can't get hot enough to trip that "spring" and open the points ongoing.

Or, I might be completely wrong and the flasher has nothing to do with it the problem at hand, but this was my experience,
(';')

 

ok Elinor, so the problem disappeared with an LED bulb ?

 

Jose, it started on one side, then neither of them decided to work. The Moss supplied relay did exactly the same behaviour as the replaced original. Tomorrow I'm in the garage to sort this mess out once and for all. I keep circling back to the Hazard switch as that ******* supplies the entire Indicator circuitry as far as I can work out, Either directly from the Battery or via the ignition switch. It's those pesky diodes also. I have a plan. Ian

 

Elinor you maybe exactly right. The led flasher is a timed, solid state flasher instead of a thermally operated and was required on my 71 corvette to make things happy after installing led bulbs. Works great. Btw... got my flasher from Orielly's Auto Parts off the shelf.

 

Ian, very possible it has to do with the Hazard switch, but in my car, both indicators work fine when the hazard switch is ON.

I still think it's the Turn Signals stalk switch, at least in my car it seems.

My electrical question is:
Why would the blinking bulb lose 12volt power after being activated with the turn signal switch ?
**It doesn't go OFF, it keeps blinking but at something like one fifth the electrical power, so it is not very bright and doesn't light up the green arrow indicator.
And it only happens with the left side signal.

 

No, LED bulb Was the problem.
(';')

 

misunderstood or misread. I don't use LEDs anywhere, only the factory type bulbs.

 

Ian and Doug,
in my car, 1983 build, 1984 model, the tachometer harness and its turn signal bulb socket has a plastic "american" type of socket and bulb, (bayonett push-in), BUT the speedometer has the old style "british" bulb metal socket, ​​​​​​(push-in bulb and rotate to secure in socket).

there is no evidence of a splice or replacement at the tachometer wiring harness turn signal bulb socket, (again), specifically at the tachometer Left turn signal bulb indicator.

The tachometer harness disappears into the main harness, there is no "plug" either;

Did these cars come like that from the factory ?

 

Your description of how the standard flasher works and why it won't work with LED bulbs is spot-on, Elinor. I'll add to the thread that I tested both bulb sockets and got no voltage on left or right when stalk was applied. I can still hear the flasher and the external lights work as normal. I haven't moved this issue up the "to do" list yet.

Dave

 

The flasher warning lamps are wired in a slightly unusual way on these cars. The flasher unit has a single teminal for the warning lights and the signal from this terminal is sent to both the left and right warning lights when the flashers are on via the diodes. The ground path beyond the diodes is via the external flasher lamps for the OPPOSITE side.

So if you are turning LEFT, the warning lamp in the tacho gets voltage form the flasher unit, which passes through the diode then is earthed by the RIGHT HAND external flasher lamps. Meanwhile the warning lamp for turning right (in the speedometer) receives voltage at the same time but does not illuminate as there is the same voltage present at the anode of the diode which is connected to the LEFT HAND external lamps.

In the attached wiring diagram, I have highlighted the current flow for turning left with extenal lamps in green and the warning lamp in yellow to illustrate.

If all the bulbs have been changed to LEDs, this will prevent the warning lamp from illuminating, as the path to ground via the LED(s) in the external lamps is too high a resistance.

I just simulated this by wiring a small LED warning lamp bulb to a 12V power supply. First I checked it lit up normally just connected between + and - of the supply, which it did.

Then I wired the ground lead via a standard automotive filament bulb. The LED warning lamp lit up and the filament bulb did not. This replicates the Jaguar wiring.

Next I chaged the filament bulb for an LED bulb (after cheking this LED bulb was working normally and connected in the correct orientation). Neither of the LED bulbs lit up.

So to resulve your problem, I believe you need to replace at least one of the external flasher bulbs in the car with a standard filament bulb on each side. This should restore the ground path to the warning lamps.

 

Andy T,
Thank you for your detailed description, unbelievably NOT intuitive. Jaguar engineers stayed awake many nights to come up with that method. I changed all turn/tail/brake/backup bulbs along with LED flasher when I was rebuilding the car. Didn't know how/if the original setup worked, just assumed all bulb sockets had power/ground when turned on and power was pulsed by the flasher for turn signals. I will put incandescence bulbs in the front turn/parking lamps.

Thank you very much for the info.

Dave

 

Well, turns out the front indicator bulbs are incandescent as are all four body side markers, but the rear indicators were led. Swapped them for reg. Bulbs. No difference.
Put back the original Hella relay and same condition, no dash lights. So I give up!