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jimmythomson

Member Since: 18 Jul 2017
Location: Norfolk, UK
Posts: 46

Rear light setup on 300tdi

I've neglected my '96 300Tdi 110 for a while now, but finally got around to looking at the rear lights today. I've swapped out the indicators and stop/tail light for LED versions, but there's plenty of things not working the way I think they should. So first of all I'd like to clarify what people would expect the lights to do. Here's how the setup looks currently. I've added what I *think* they do:

Click image to enlarge

With the side lights on, the tail lights illuminate. If I hit the brake, the tail lights dim, and the rectangular red lights light up (but barely). The two rectangular clear lights just about work as reverse lights (they're temperamental). The fog light switch doesn't appear to activate anything.

If anyone has a similar setup, could you tell me how your lights operate? Sorry, I know this is a basic question, but novice mechanic here. I just want to make sure I understand how they should operate before I start tinkering.

Thanks,

Jimmy.

13th Jan 2019 5:46pm

Romadog

Member Since: 07 Jul 2011
Location: Powys
Posts: 1749

Your fog lamps are the rectangular ones.
You seem to have shown that you have two pairs of Brake lamps.

13th Jan 2019 6:01pm

jimmythomson

Member Since: 18 Jul 2017
Location: Norfolk, UK
Posts: 46

Yeah, that was what my assumption, unfortunately the fog light switch does nothing, and those light also come on dimly when I press the break pedal

13th Jan 2019 6:06pm

jimmythomson

Member Since: 18 Jul 2017
Location: Norfolk, UK
Posts: 46

Ok, so just tested the fog light switch again and it's now illuminating the left hand side rectangular red light. Should the right hand side illuminate too? I'm guessing so.

13th Jan 2019 6:16pm

VVS210

Member Since: 12 Nov 2016
Location: Hampshire
Posts: 953

Sounds like you have got an earth problem there as well. Probably worth you making up a simple test light using a bulb holder & some crocodile clips so you can test switches & connections at the lights. A meter that you can check continuity with would also be handy too.

13th Jan 2019 8:10pm

jimmythomson

Member Since: 18 Jul 2017
Location: Norfolk, UK
Posts: 46

Right-hand fog light now working after cleaning up the contacts on the light unit.

Just waiting on the arrival of another stop/tail light after I dropped one on to solid ground

I've also got indicator issues with both indicators coming on when indicating right or left. I believe it's to do with the switch to LEDs. There's plenty of stuff online about the problem. I want to properly understand it before I make any other purchases though. If any auto-electricians can give a really clear explanation it'd be appreciated. I'm currently trying to understand the problem from looking at the electrical diagram for the indicators here: http://duud.ee/LR-manualid/300Tdi_Wiring_Diagrams.pdf#page=23

14th Jan 2019 5:51pm

jimmythomson

Member Since: 18 Jul 2017
Location: Norfolk, UK
Posts: 46

Starting to get my head around the circuit diagrams, but was hoping someone could tell me what the piece of circuitry that I've highlighted in red is:

Click image to enlarge

Thanks!

16th Jan 2019 3:24pm

dorsetsmith

Member Since: 30 Oct 2011
Location: South West
Posts: 4554

highlighted in red is: logic gate in side the switch not fixable

Land Rover Defender Hazard Warning Light Switch - Yuf101490

16th Jan 2019 6:22pm

jimmythomson

Member Since: 18 Jul 2017
Location: Norfolk, UK
Posts: 46

Thanks, but are you able to elaborate on what the logic is exactly? I'm trying to fully understand everything going on in the switch, but can't find any clear electrical circuit symbols that map to what I've highlighted.

Ta.

16th Jan 2019 7:42pm

grafty99

Member Since: 15 Aug 2012
Location: North Devon
Posts: 4785

I don't want to be "that guy" but you might want to swap the positions of the fog and reverse lights.

Legally, fog lights need to be a minimum of 100mm away from a brake light, they look a bit close

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1990 Vogue SE
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16th Jan 2019 8:51pm

jimmythomson

Member Since: 18 Jul 2017
Location: Norfolk, UK
Posts: 46

Thanks, Grafty That's good to know, and should be an easy switch I think.

I found a reference to this in the document 'Regulation No 48' from the ECE, but interestingly couldn't see anything about it in the MOT testers manual.

I might use it as an excuse to upgrade to Bearmach's LED fog/reverse lights.

Thanks again!

16th Jan 2019 9:20pm

grafty99

Member Since: 15 Aug 2012
Location: North Devon
Posts: 4785

It's a strange one. Something can pass an MOT and not be road legal (go figure).

Basically an MOT just checks that everything is working as it should, not that it is necessarily legal.

As fog lights are high intensity they may dazzle and mask the brake lights so it is actually a regulation that makes sense

16th Jan 2019 9:33pm

Martin
Site Admin

Member Since: 02 Apr 2007
Location: Hook Norton
Posts: 6605

2015 Defender 90 Puma 2.2 XS CSW Montalcino Red

There's no electronic logic in the hazard switch - the pre-2002 switches almost pre-date the valve never mind electronics

I think the gates have been used as a round-about way of showing the mechanical switching.

With the switch in the normal (off) position, the ignition feed (pin 8, GREEN) is connected to the output to the flasher relay (pin 5, LIGHT GREEN).

Nothing happens unless the ignition is on and the indicator switch connects one side or the other to the output from the flasher relay. Then you get indicators that side.

With the switch in the on position (hazards on), the ignition to flasher link is cut (bottom "relay"). Now:

Permanent 12V (pin 7, PURPLE) is connected to flasher relay (pin 5, LIGHT GREEN).
Feed from flasher relay (pin 2, LIGHT GREEN WITH BROWN) is connected to the left indicators (pin 3, GREEN WITH RED) and right indicators (pin 4, GREEN WITH WHITE) and the warning lamp (pin 1, BLACK WITH RED).

So the flasher relay is fed power, and both indicator feeds (plus hazard warning light) are connected to the output from the flasher relay.

Hey presto - hazards!

The real internal diagram is like this:

Click image to enlarge

1988 90 Td5 NAS soft top

2015 D90 XS SW

16th Jan 2019 11:13pm

jimmythomson

Member Since: 18 Jul 2017
Location: Norfolk, UK
Posts: 46

Thanks, Martin. That's really useful stuff. I think I've now got my head around it all.

I'll report back with an update once I've had a chance to try a few fixes.

Thanks again!

16th Jan 2019 11:47pm

dorsetsmith

Member Since: 30 Oct 2011
Location: South West
Posts: 4554

Past and copy

Last edited by dorsetsmith on 21st Jun 2019 8:38am. Edited 3 times in total

17th Jan 2019 8:04am

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