L322 Range Rover rear light upgrade question

[Chlorothalonil]

Just in the process of fitting 2010 LED rear lights to my 2008 car. Only issue is the low power tail light feed for the old filament lamps (increases power when fog light switch pressed) is causing the fog lights on the new clusters to illuminate at low power as soon as the main lights are on. Gets brighter when fog switch pressed.

Online guide suggest a kit from Powerful UK but this doesn’t work properly on mine, so I was in the process of fitting a relay to solve this. Does it need a diode or resistor fitting, as quite a lot of online electronics sites refer to needing a diode in conjunction with a relay to prevent voltage spikes when being switched off.

Any help would be appreciated!

[The Wookie]

If the issue is the potential for voltage spikes when turning on and off then when selecting a relay make sure it’s got a fly back diode, and that you wire up the pins to the coil the correct way round

[Chlorothalonil]

I’ve got some 12v diodes and also some Zener diodes on the way but not sure whether these are suitable?

[Chlorothalonil]

The relay itself doesn’t come with a diode unless it’s fitted inside? But I doubt it.

[The Wookie]

Chlorothalonil said:

The relay itself doesn’t come with a diode unless it’s fitted inside? But I doubt it.

Some do, it’s basically there to allow the current to run down within the relay rather than creating a spike. That said it’s within the coil side and it’s primarily to protect the switching ECU from the inductance of the coil

I don’t suppose you’ve got a wiring diagram of the old and new versions?

[Chlorothalonil]

Unfortunately not but I know the old tail lights with filament bulbs ran at 5W but the supply increased to 21W when the fog light switch was on. With the new lights the tail lights are separate but the fog comes on at a low level with them. Someone posted a circuit diagram for a relay and latterly mentioned the diode. Just wondered if this could be wired in between the input wires and the relay.

[Chlorothalonil]

The circuit boards from Powerful UK seem to have various relays, resistors, diodes and I think capacitors. They are designed to correct the bulb warnings and the fog light situation but I had disabled the bulb checks with my iiD tool, which just leaves the fogs coming on at low power with the lights.

The boards they sent stopped the fogs coming on but made some electrical noise and caused the tail lights to flicker quite noticeably; I don’t really need the other functions the boards are designed to perform so thought the diode/relay route would work instead of that makes sense?

[Chlorothalonil]

[The Wookie]

I daresay it’s already got the diodes it needs to work

There may be a faulty component on the board, also worth checking everything has a good earth as although I don’t know enough to have a guess what the function of the board is, presumably there must be some balancing going on to differentiate tail from fog and a bad earth could cock it up.

[Chlorothalonil]

Cheers - one side made lots of noise and the other seemed ok but both produced a lot of flickering so I’ve taken them off for now.

[The Wookie]

Chlorothalonil said:

Cheers - one side made lots of noise and the other seemed ok but both produced a lot of flickering so I’ve taken them off for now.

Had a look at the website for it, one of the things they mention is towbar wiring, vehicles of that age have been around long enough to have dodgy wiring installs fitted then removed. Worth having a look if you haven't already

A few years ago a mate was having some issues with his one, opened up the right rear boot panel to find a rat's nest of scotchlocks and badly chopped wiring from where it had previously had a towbar. Moronic when there's a socket for the Land Rover wiring right next to it which is plug and play.

Failing that double check your earthing points or even try giving it a direct ground to see if it changes anything

[Chlorothalonil]

I’ve taken the boards out now and am looking to install the relays but am getting a bit puzzled by what type of diodes and resistors I need; one or two on the RR forums claim to have done it this way but haven’t specified the detail.

Is there some way of working out the ratings?

C