Should H4 headlights have relays wired in?

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Webley1991

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My Series 3 came with H4 headlights installed when I bought it. The lights seem to be bright enough and I have luckily never had anything burn out as yet.

There are no relays fitted into the wiring. I did replace a lot of the lamp wiring and fitted new crimp terminals when I rebuilt it. I would hope there isn't excessive resistance anywhere.

I haven't actually driven much in the dark, so haven't made much use of the lights. Are H4 lights without relays guaranteed to cause problems eventually?

Thanks for any replies.
 
It wont hurt, when I upgraded to H4 I didn't bother as I didn't think the wattage that to much different
when I put lucas fog and spots on I used this guide

lights.JPG
 
On a series, the weak spot is often the switch. The constant making and breaking of the contact causes resistance between the contacts and this can lead to the switch melting. All of the wiring and electrical components on my series 3 are original except the starter motor, solenoid and the horn, I don't have any relays. If I was going to upgrade the headlights, I would fit a relay.

Col
 
If you stay with the H4s I would fit relays, the contacts will burn out eventually and its a lot eaiser if its the relay contacts not the dip switch or light switch.
 
SIII PETROL WITH FOG AND HEADLIGHT RELAY ADDED.png
assuming its petrol and neg earth the alteration via steering column relays hidden behind dash I would use fused relay for extra peace of mind https://www.12voltplanet.co.uk/make...tacts-12-volt-30-amp-integral-blade-fuse.html theView attachment 187285 option is to use the spare fuse way and wire the feed to fog lights from there so you would have to fit link wire (white) from fuse holder 3 to holder 2 this would avoid the fog lights working with out the ignition being on and the head lights on dipped and give you some lighting if the headlight or fog's decide to react with water or the dreaded tin worm in the middle of nowhere
 
Last edited:
In mystery's excellent diag above, the full headlight current is still going through the light switch, which somewhat negates the benefit of the relays. My suggestion would be to feed the relays (terminal 30) direct from the solenoid/battery via a strip fuse - although I would still use the fused relays, the strip fuse is just to protect the feed into the relays.
Headlight relays1.png
 
Yes do the boomslang conversion, I have replaced three headlight switches in two years and narrowly avoided a fire. It took me the best part of a morning to fit the Boomslang loom, I can post photos if it helps.
 
I haven't fitted relays to my halogens. It's something I've often considered but I do such small mileage and probably only drive it in the dark twice a year. Maybe one day...
 
Thanks for posting the diagrams. Now I think of it, the headlamp switch was not original when I bought it. I replaced it with a used original that I bought at one of the shows. Perhaps it had burned out in the past.

As the switch is the weak point, would fitting a switch rated to a higher current be cheaper option?
 
are you talking about the lighting switch or the column main/dip switch doubt if you find a higher rated lighting switch and the main/ dip/flash column switch no chance
the trouble is repro's as such are not constructed using the same materials as the original,you find copper replaced with coated steel parts ,from the original switch contacts using silver alloy hate to think what they are using to replace it with .there's also the problem of knowing if the item is genuine or a cheap fake the Chinese are good at not adhering to copy write laws ,just because it got Lucas stamped on it doesn't mean it genuine so good luck with that
 
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