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o4dn

Member Since: 08 Jan 2010
Location: South West
Posts: 549

2009 Defender 90 Puma 2.4 SW Alaska White

Light switch and relay

There is something I am not quite sure about the wiring of the headlamps on the Defender (and on the Series as well).

To protect the light switch from deteriorating and eventually melting, and also increase the brightness of the headlamps, I added a separate loom with a relay (a Boomslang), something I did years ago on my Puma Defender, and that I am now planning to do on my Series 3 as well.

I vaguely remember that the reason was that the light switch was not protected by a relay. But looking at the electric diagram, it appears there is already a relay for the headlamps:

Click image to enlarge

So now I am confused as to why a separate dedicated loom such as the Boomslang would make any difference for the switch and the brightness of the headlamps…

Can someone enlighten me?

“A Land Rover immobilized is a moral defeat for the driver and bad publicity for the vehicle, […] it's up to you to do justice to your Land Rover!” - Land Rover Driving Technique.
--
2009 2.4 Puma Defender 90 SW
1979 Land Rover Series 3 88"

2nd Dec 2022 4:37pm

blackwolf

Member Since: 03 Nov 2009
Location: South West England
Posts: 17540

2007 Defender 110 Puma 2.4 DCPU Stornoway Grey

The relay is present to switch the headlights off when the ignition is switched off, it doesn't prevent the full headlight current from passing through the switch.

2nd Dec 2022 4:43pm

o4dn

Member Since: 08 Jan 2010
Location: South West
Posts: 549

Thanks blackwolf, that's very clear!

2nd Dec 2022 4:53pm

TexasRover

Member Since: 24 Nov 2022
Location: Paris
Posts: 1118

2002 Defender 110 Td5 DCPU Chawton White

The lights will also be brighter because the relay and power source are all close to the headlight reducing the voltage drop over the wires. The grounds is local, but if you need to extend the power cable make sure you use heavy gauge

2nd Dec 2022 6:41pm

o4dn

Member Since: 08 Jan 2010
Location: South West
Posts: 549

Yeah, good point, I expect the fitting on the series 3 to be a tad more challenging... “A Land Rover immobilized is a moral defeat for the driver and bad publicity for the vehicle, […] it's up to you to do justice to your Land Rover!” - Land Rover Driving Technique.
--
2009 2.4 Puma Defender 90 SW
1979 Land Rover Series 3 88"

2nd Dec 2022 7:29pm

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