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

Well the good news is everything works, thanks to Richard's help and patience I can turn my fog lights on from my dash mounted Durite illuminated toggle switch using the existing wiring in the loom.

The only disapontment is I can't get the little LED on the toggle switch to light up when I switch the fogs on

Perhaps I've not got the wires on the correct switch terminals but I did try a number of permiatations and I can only get either the fogs to work or the LED in the switch to work, but I can't get the switch to illuminate when I turn the fogs on?

Here are the three wires:





And here's the switch.



I'd love to understand what I'm getting wrong?

On the switch two of the terminals are the 'switched' line, the 3rd one needs a neutral (earth) feed to be able to light the LED, but not easy to fathom from above, (I tend to test new switches with a multimeter)

If you check the Durite specification, Terminal 1 is +ve supply, Terminal 2 is the load (fog light);and terminal 3 is -ve (or ground or earth) Looks like you have not connected 3 to earth and… if you happened to have connected 1 and 2 the wrong way round, the led will be on permanently.

Interesting chaps, sadly none of the permiatations deliver the desired result

However, moving on from the switch wiring I can confirm the circuit works just fine.... until that is I start the engine. With the engine running if I switch on the fog lights the fuse/fuses for the off side tail light and all the dash lights blow immediately

Where's RichardV6 when you need him

To be fair, I do recall Richard saying (prompted by Rog) it would be a good idea to up the o/s sidelight (fuse 12) from 7.5 to 15 amp, that may well bring back my dash lights and O/S tail light but I'm still foxed on the lack of switch illumination

Yup, the fogs definitely blew the 7.5a rated fuse No 12, with the engine running



I simply replaced it with one of the 10a spares In the box and normal service was resumed.



Still no switch illumination though

Dave I’m no expert but I would drive no more than a relay off those plug and play wires. I wouldn’t increase the fuse size either. Richard will be along soon.

This pic any help?

First mention of a relay Rog

I also think if an additional relay is required we need to stop using the term 'Plug-N-Play Waringstown.

Kind of makes me feel like I should have fitted the auxiliary front light loom I've got on standby with it's dedicated relay and fuse

However, what I can say for sure is the load from the fogs definitely blows a 7.5a fuse, however,
up the fuse rating a fraction to 10a and its all good 👍

I'd be very surprised if the wiring and circuit I've used doesn't include a relay, afterall the wiring has been put there in the loom with the specific purpose of running front auxiliary lighting.

I'm also comfortable the circuit is safe as its clearly protected by fuse 12, and while the load did blow the 7.5a fuse this was actually a good safety test and we now know the circuit happily runs with a 10a fuse too, so its not like there's excessive load on the circuit and 10a seems to support my calculations.

As we know, amps = watts / volts, so that would be 55w / 12v = 4.59 amps x 2 lamps = 9.18a

My Marchals are rated at 55w each so it's no wonder the 7.5a fuse (fuse 12) blew, upping it just 2.5a to a 10a fuse worked supporting my calculations but at just 0.82a over the predicted load it's a little too close on the fail rating for my liking.

I'd prefer to run a 12a fuse instead which gives a safe margin of 2.82a over calculated load and is still only a 4.5a increase over the 7.5a fuse originally designed to just protect the O/S side lights.

I'm comfortable with the circuit now that only works with the car's side lights on exactly as you'd expect, I will up my fuse 12 from 10a to 12a but that's all it needs to complete the project and make the circuit both safe and reliable.



The setup includes 20,000 lumen 3000k (traditional halogen colour) LED H4s under yellow glass globes for the headlights, supported by beautiful period chrome Marchal fog lights running yellow traditional incandescent 55w halogen bulbs. The light output is outstanding especially as I've chosen to go yellow, the cutoffs are really sharp so while some adjustment is needed I'll sort this after marking up and then copying what my 2021 Toyota C-HR projects on my white garage door.

However, I'd still like to get my illuminated toggle switch to light up.

To explain how I've wired the up the lamps currently, firstly I'm grounding my Marchals from lamp to chassis rather than tapping into the headlight grounds as recommended by Richard, secondly I couldn't find the blue/yellow wire on the N/S so ended up just extending the O/S blue/yellow wire across the car to power the N/S lamp.

This all worked out fine, but I suspect its also why I've got no power to the switch LED.

The switch LED is connected between terminals 2 and 3, with 3 being earth. So when the switch is turned on, terminal 2 then becomes live sending current to the fogs and also sending current through the LED to earth. The LED should be independent of whether fogs are connected or not.
Possibilities are:
Poor earth to terminal 3
LED has failed
Could it be working ok but, because of the position of the switch low down,, you cant see it as you are not looking directly at the end of the toggle (it may not be that bright)

If no joy, I would pop the switch back out and test it on the bench using a battery connected directly to terminals 2 and 3, but make sure 3 is -ve as LEDs are usually polarity sensitive.

I would also be wary of upgrading fuses unless I were sure of the rating of the wiring. Just because “it works” doesn’t mean it’s safe. It may well be ok, but just saying it’s not good engineering practice. Not sure you will find a 12 A fuse either.
That’s where the benefits of relays come in where the whole circuit can be wired and separately fused to suit the load.

Dave, starting with the light switch, simply connect up as per Doug's instructions using a chassis connection you will have to find/provide to allow warning LED to illuminate. You can ignore the second red/orange wire as it's not part of the intended fog light circuit, and it doesn't matter which since they are joined at a common bomb tail further up the loom that shares sidelight feed. Remember red/orange is feed to switch and blue/yellow the switched load out to your foglamps.

Fitting a relay is an option but adds complexity. MMC don't use them anywhere in the main lighting system including headlamps. My own advice is to do without assuming the switch you bought is adequate for combined fog light load. You will need to uprate fuse 12 to 15 amp though (as you've found!) given this is nearest common value to allow a load margin, and as previously suggested. Cable size will be fine, indeed I've found plenty of copper in loom when baring the admittedly thin insulation on wires.