XJS Headlights won't flash
 

My 1991 5.3 XJS headlights refuse to flash (when light switch is in off position) , however when the lights are on the dip/main beam works fine.
The front fog lights have been temporarily removed ( not sure if this would have any influence). Is this a relay issue? The C38616 relay is £40 so don't want to order one until I'm fairly sure that will fix things. Any advice would be appreciated.

Cheers

Steve

Are you sure it's supposed to flash when headlights are off?
I don't have a 91 wiring diagram but my 95 diagram shows you need power to the headlight module (Module supplies the low/high beam power through a momentary selection of the stalk switch). The only wayt o get power to the module is to turn on the headlight switch whcih powers the "headlight Relay" which supplies power to the module.
Again, 95 may be different than 91 but see diagram of the 95 below and see what I mean.
https://cimg8.ibsrv.net/gimg/www.jag...4d201b1b71.jpg

You have to be able to flash your headlights in daylight so as to advise the moron in the Beemer who is headed straight at you of the error of his ways!
Most cars came out without the front fogs so having them missing shouldn't affect the operation.
It could be a dodgy relay or build up of gunge on the light stalk contacts.

...But he said it works fine with headlights powered on. hmmmmm.

So it looks like " 4" is the Batt power that supplies the 12V to the high beams and low beam,....s but with headlight switch off, the module is not powered to perform the "toggle" from low to high, high to low but still somehow powered to only toggle the high beams when normal headlight switch is not selected. That means that there needs to be a secondary power source to the module to effect pulling the internal coil when high beams selected to close the contact(see red path) momentarily.
"13" for the headlight relay coil, comes form the Load Relay.
So somewhere, un-switched headlight power would need to get its power from someplace other than the headlight switch relay to power just the high beams.



https://cimg5.ibsrv.net/gimg/www.jag...5179c0bb9e.jpg

https://cimg7.ibsrv.net/gimg/www.jag...75813430fa.jpg

Not being able to flash is cramping my style! The MOT man wasn't impressed either as he failed the car on daylight flash. The flashing function does not occur in any master light switch position - should have made that clear from the start. If the lights are off and I pull the light stalk towards me and then turn the lights on the main beam comes on straight away - not sure if that is relevant. Just to reiterate - the dip/main beam function works OK. I'm relieved the fog lights won't affect things as they were well and truly knackered so took them off in case they would be MOT failures too. Carsnplanes - what can I say - fantastic detail. Looking at your diagrams - are you saying I might need more than one relay - the one labelled lighting and turn signal switch and the number "13" headlight relay. I guess these relays are the ones near the fuse boxes on the LHS of the engine bay? Steve_M - will check out the light stalk contacts ... probably will have to wait until weekend.

If the lights are not flashing and the lights work on the switch, then the flash circuit is at fault. You do not need extra relays or anything like it; you just need to carefully test the actual flash circuit, right up to and including the lights relay (headlight control module) itself. It is always possible that the relay actuation is allowing the lights to work on the switch but not on the flasher stalk. Your car has Ford switchgear, so any decent car electrician can do the testing, if you need help.

Greg, I'm reading his complaint that everything works perfectly being able to toggle High and low, etc, but only with master headlight switch in ON position. From reviewing the diagrams, the module provides the momentary high beam/low beam action when a ground is provided by the momentary pulling of the stalk towards you. This is a common flip flop type circuit. But for the module to do this, the module needs to have full 12V power to provide this. Complete powering of this module is provided by the commanded headlight Relay by the master headlight switch. Ok, so all that action was with the headlight switch on.
With the Master headlight switch off during the day, if the high beams are expected to flash, then there has to be a a power source to pull the High beam only coil leg inside the module to close the high beam leg contact shown in red. Not to toggle high/low, but just to momentarily close that one high beam leg. That 12V command power seems to be what's missing. The ground is there from the stalk switch pulling, but power for that coil needs to be there from Batt when main headlight relay is not powered from the master switch. Perhaps one of the legs in between the master relay and the module is battery power and is not there, or something got messed up around the Fog Light connector. I don't remember if the jumper is supposed to be in there with Fog Lights connected or not.

Does anyone have the headlight schematic for a 1991 UK market car?

If no joy after cleaning all relevant connections and grounds, that's where I'd begin, personally. Finding the known-correct schematic. But, that's just me :)


Cheers
DD

So looks like the 91 does not not use a "module"...and I apologize for posting diagrams of a 95 with module. I'm sure this caused confusion.

The '91 just uses a relay instead of a module where the momentary stalk movement closes a switch to pass ground to the pull coil in the relay to flash the high beams. Constant power for the relay is from the left terminal post.
For normal headlight power, the rotary switch passes power to the normally closed contacts, then to the bulbs. When High beams are selected, it opens the normally closed low beams and moves o the high beam contacts so that you only have high beams on.
Ensure you have 12V to the 81A coil power terminal. Confirm ground at 31B when stalk is flashed. The upper leg is used to flash when normal light power switch is off. The lower leg is used when main light switch is on and removes low beam power to connect to high beam.

https://cimg1.ibsrv.net/gimg/www.jag...2b46825a44.jpg

Those schematics are pretty cool. Looks like to test the relay all I need to do is see if there are 12V on 81a (far left of picture , brown lead at back?) when the light stalk is in flash mode and then test if 56a (blue lead at back?) has output volts as well. Will let you know how I get on at the weekend. It will be one happy day when that car gets through the MOT - I bought it in 2014 and it's been off the road since 2015! Thanks everyone for helping me out.

If you say your high beams work when master rotary switch is selected on, then the high beam switch is pulling the coil and removing power from the low beam output and moving it to the high beam output properly, so we know the lower leg is working and we know we have power at 81A. What we don't know is if the upper leg is working which provides power from 81A to the high beam output 56A when master rotary switch is NOT on. In this case if the upper leg isn't working, it would be the relay. Looking at the relay you show, I bet you could open it up and clean the leg contact and would be as good as new. Those metal relays are easily opened and can be cleaned up.

Where is the main/dip switch in this circuit? I can't see how the normal lighting circuit works........maybe I'm just being thick :-)

So still don't see the main/dim function...I guess I am thick.

Follow the the starting point of 12Volts from the "Left Terminal Post". Leaving that post and heading south and going into the rotary headlight switch,12V is waiting there for you to turn the switch on. When you do, 12 V will pass through the switch and head north then turn east to terminal 56 of the relaxed normally closed lower contact of the relay. It's relaxed because it is not energized, by the high beam switch stalk. So 12volts passes through the lower contact and out 56B to fuse #4 and #2 then to their respective bulbs. All this was Main lights ON- LOW beam.
Now...on the extreme right of the page (yellow highlight path) you see a path to ground with a switch in the middle. This is your high beam switch. When you momentarily pull it towards you, you "make" or close the switch, thus providing a momentary ground to the only coil in the headlight relay which pulls up both contacts to power the high beams. The lower one pulls up and away from the low beam output and moves the 12V to the High Beam output. Just another set of outputs to brighter bulbs. The stalk when pushed forward provides constant high beams due to the stalk detent in High.
When main headlight switch is off, high beams can still be achieved by a momentary pull on the stalk and it will again provide the necessary ground to pull the relay contact up (upper contact will provide the high beam path because no power is going to terminal 56 through the headlight switch on the OFF position.)
So there you have it.
Hope that's clear as mud.


https://cimg9.ibsrv.net/gimg/www.jag...7a9db7bf10.jpg

Carsnplanes, thanks for your very detailed explanation. So it sounds that the piece I was missing is that the flash switch is not really the flash switch, it is the dip/main switch that also has a flash function. By the way, I looked at the schematics in a 1990 service manual and it shows a circuit similar to that detailed at the very top of this thread, not the simpler one. I think the Hella device shown in the photo is in fact the headlamp control module shown in that original diagram. So going back to the OP problem, terminal 81a (blue/black) should be grounded by the flash function in the stalk which should then trigger the module to connect the 12v on terminal 30 straight through to terminal 56a (blue/white) high beam output.