Talk Morgan Forums Morgan Sports Cars Maintenance & Servicing Fog Light Wiring

Just to conclude, if you're using Morgan's embedded auxiliary lights loom and run 2 x 45w halogen bulbs a 10a fuse 12 is essential, the original 7.5a is definitely too low but you do not have to go up to 15a, 10a works fine.

Saying this, I'd recommend combining Morgan's aux light loom in conjunction with a relay and using a 10a fuse between the battery and pin 30, you now have a properly protected direct feed from the battery to your lamps. Because you're now just using Morgan's circuit to switch the relay (low amp coil side), fuse 12 can remain 7.5a, I strongly suspect this will also be kinder on Morgan's delicate PCB dash module that I recently had to have repaired on Monty.

However, with my Marchal fogs now running LEDs no relay is requited, if I add up all the bulbs on fuse 12 now I get a maximum of 30w, so that's 30w / 14v = 2.14a meaning only a 3a is needed, I've actually gone a little higher at 5a the circuit is working perfectly while still being properly protected. I feel I now have the simplest, neatest, reliable and most importantly the safest way to wire auxiliary lights using Morgan's embedded aux lights loom, but only because I’m using LEDs in my Marchals.

If you want to stick with incandescent bulbs in your auxiliary lights my advice would be to fit a relay as originally recomended by Roger, the relay could either switched by Morgans circuit or perhaps better still forget it altogether and install a dedicated aux light loom with relay and dedicated fuse for the safest instalation of all.

Dave they look great. Have you had any problems/indications with the INRUSH current you get when switching LED lights on, thinking of that PCB.
I had trouble with a light timer. Granted for outside lights, caused by the inrush current. Hence my wondering. Info Here

According to Dave's reports he eventually wired the fog switch up as per provisions made in the MMC loom. This takes a feed from fuse 12 (7.5 amp) labelled as "o/s sidelights and dash illumination". Clearly there is a need to uprate this fuse. The extra current flowing through it has no bearing on the PCB. Dave's recent issue was because he thought he could manage without uprating this fuse. See my post here from over a year ago.

I would have been inclined to avoid the complexity of an extra relay despite the extra current for fog lights flowing through sidelight circuit, as it's switch contacts are designed to handle the higher current from headlamps, but accept it's a matter of personal choice. Irrelevant now since LED's being used though.

I think the inrush current issue you mentioned is relevant only to far larger LED installations.

No Inrush issues.

I also note the above paper seems to be referring to a 240/110v AC mains wiring system in a house, so I'm not sure how relevant it is in an automotive 12v DC situation? I certainly ran LED H4s in my TVR for years and never suffered any such inrush issues.

One thing I can confirm is the Marchal LEDs have massively lowered the load on Morgan's embedded aux lighting circuit that’s protected by fuse 12, to be sure on this I have multiplied the total bulb Wattage on the circuit and carefully logged my battery voltages too using my EMU Black ECU software that confirms the alternator regulates perfectly between 13.4v - 13.7v.



There is dip to 9.2v under cranking when starting the engine which then spikes momentarily to 14.78v, but this is perfectly normal and to be expected, I should also point out the whole dip & spike episode spans less than a second in time before the situation returns to the well regulated 13.7v.



Based on my calculations, and now supported by real world testing the 5a fuse 12 I'm running has proved itself to be perfectly sized. However, given that the dip & spike on starting is where I'm most likely to experience an issue I repeated a number of consecutive cranking tests with the Marchals left on, and I'm pleased to confirm all was fine

As the above photos show, the Marchal LEDs do give off a light that's more on the amber side of yellow, I'm currently on the fence regarding this hue as my headlights are a nice vintage French yellow and I had originally hoped to achieve a match with the Marchals, but I accept you can overthink these things and afterall amber is period correct as it was found on Wipac Grey Nights and Raydyots if people can remember those lamps?



When all is said and done and now I know how delicate and problematic the PCB dash module is, I have to say if I had my time again I would have simply used the separate aux lights loom (with relay & dedicated fuse) I purchased specifically for the Marchal fog light installation. However, the new Marchal LEDs pull so much less current I'm confident a relay is no longer needed and my PCB is now perfectly safe.

Since this is a fairly detailed discussion of fog lights - could I extend to ask a more general question. I have a pair of Lucas auxiliary lights on my Plus 8 (1977). I'm trying to decide if they are fogs or spots:



This is the offside light:




and this is the nearside light:





My understanding was that fogs have the vertical ribbing on the lens front all the way across the lens - but spots don't.

Here the nearside light, has ribbing only in the centre of the lens, and the offside light is ribbed across the whole of the lens?

So are the spots or fogs? Is it usual to have different lens on offside and nearside?

A lot depends on how they're wired in - spots usually come on with main beam, and extinguish when dipped beam is selected, and fog lights usually have a seperate switch with a tell tale - the switch is live when the lights are turned on - sometimes side, or sometimes with dipped beam.

Clear glass usually gives a long, narrow beam (more suitable for a spot) and ribbed glass gives a shorter, wide beam more suitable for fog.

Thanks, these are manually switched and if turned on, are actually lit up when either main or dip beam is on. The thing that puzzles me is that they are not a matched pair, and even appear to be one spot and one fog. I don't think having both spot and fog on simultaneously is great - since the spot will simple dazzle if it is foggy.

Running one spot light and one fog light was common practice back in the day, it looks like this is what you have but they've just been wired up incorrectly.

On closer inspection, the offside is a Lucas FT6 and the nearside is a LR6 - so fog on the offside and spot on the nearside. Which seems odd, as surely you would want the fog lamp to be on the near side, so that it illuminates the kerb?

Montegue - what would be the correct wiring? spot only on when on main beam and fog only only on dipped beam ?

thanks

Spots only with Main beam.

Fogs can be on with side, dip and main.