Talk Morgan Forums Morgan Sports Cars Maintenance & Servicing Rear fog light on 2011 Plus 4

All, My rear fog light refuses to work. No 12Vto the light. There is a good fuse and the the rear fog switch brightens as you would expect when you press it ( doesn't when you remove the fuse). Is there a relay for it somewhere and if so where? Or I'm down to tracing wires from the switch

Have a look at this thread. Can't praise Rog enough together with the other contributors. Best of luck.
https://www.talkmorgan.com/ubbthreads.php/topics/792494/1

Sadly no conventional relay, but lots of components on the pcb, behind the dash. Certainly investigate the wiring first of all but it could well be the dreaded faulty pcb. As Salmo indicated, lots about it on the thread indicated.

To shorten the search and maybe make life easier for you, Thread #792200 of the above posting details what Rog did to fix his pcb by simply replacing a transistor. ((That was after he had replaced everything with his own designs)
So, if your fault is similar, it could save you having to replace the whole gubbins.

Before i dig my oscilloscope out. Does anyone do a repair service on that card? Or is this a new market I've opened up?

As others have said it may well be the PCB board if a simple poor connection is not found. There is a rear fog light relay that provides conditional (headlights need to be on) power to fog light when selected. Unfortunately this hard wired micro relay is an integral part of the PCB. Have a look here for Rog's investigation into a "stuck on" rear fog light, noting that relay driver transistor required replacement. I appreciate your issue is the opposite but note that one headlamp mode or other needs to be selected.

Cheers Richard, Could still be the transistor. I'm assuming that Rog' was collector /emitter short, but i now have a good idea where to look. I might copy that PIC if I can as well

Perfect! I think you have just found yourself a new business opportunity

Its intriguing that the fog instrument lamp changes its bright state when pressed. I believe the normal low 5v state power comes from the ignition supply but the bright state is initiated from the 12v fog lamp supply (fuse.5) when the relay is switched. So that might imply that your relay and the driver tranny is functioning correctly, strange

It might be worth just dropping the dash and checking the fog light ‘power out’ pin on the pcb connector. You could poke a probe down the back of pin.6 to see if there is power or not when the button is pressed with the ignition and headlights on. That might indicate a pcb fault or a fault further along in the wiring.



But one very simple longshot first perhaps…. Sometimes these cheap little micro relays become lazy through lack of use. The electromechanical contacts have been known to stick before.

When you were testing, did you have the engine running? If not you could quickly try it with the engine running at around 2k rpm. That way the alternator will be pushing out around 14v (there’s no 12v regulation on the board as far as I can see) which will slightly increase the mag flux in the relay coil, giving a slightly better chance of freeing the contacts, should they have become stuck. You might have to press the switch several times.

Good luck.

PS - I’m sure that under some circumstances that PIC might be vulnerable. It would be great if you were able to salvage the Hex file

Interesting your thoughts on the momentary switch illumination Rog. On the 2014 on models the switches have just four connections with two of them used to illuminate dim or full brightness LED via feeds from the BCU. I don't know what voltage involved but likely the same for both intensities as dim is via resistor integral to switch. The other two switch connections are common ground and momentary switch of same to latch/unlatch BCU circuit.

It was just a thought Richard, could easily be wrong. I don’t claim to know or understand how the thing fully works by any means. It was just interesting that when mine was broken, my recollection was that the switch wouldn’t go to the bright state when it was pressed.

..... those unsupported soldered wires! Some heat shrink around the bottom of the board and wires might help

Yes it scares to see them. Probably why I'm terrified of removing the dash again