Guide to the headlamp relay mod - is one available?

[italianjob]

hello
just wondering if there was a step by step guide available for carrying out the headlamp relay modification? For fear of being told to 'search the wiki' - I have done, and subsequently read, and then re-read, left it for a few months, the re-re-read, it appears there is the half job modification where you cut into the existing wiring loom and install the relays behind the dashboard, or theres the full-monty modification where you install new feeds from directly from the battery + new earths close to the lamps + new relays behind the grill. I've want to modify my '85 C reg petrol standard 2 headlamp set up.

I'm confident enough to take the job on, but a step by step guide to this useful modification would half be useful. I see the sense in carrying out the full modification, but a few handy hints on how to start and what to avoid would be a welcome addition to the wiki for such an important and useful upgrade.

thanks in advance

[itchyfeet]

Not seen one
what you need is a good understanding of what you are trying to achieve ( which is explained in the wiki) if you don't understand wiring diagrams then probably best to learn or ask questions first.
You also need the skills to be able to make good wiring, I'm surpised how often I see bad wiring becuse people just don't have the right dexterity or attention to detail.
You also need the materials and tools.

If you have those the best advice I can give it just get on with it, you can spend longer thinking about doing something than actually doing it.

[volks_womble]

Some have used a kit that I posted a link to here: Headlamp loom upgrade kit

theres lots of discussion too, but several people have used it and found it to work. It is designed for Land Rovers, but seems to have suitable cable lengths for T25s.

Mark

[ghost123uk]

Aye, no simple "do this, then do this" write up that I have seen. As said though, it's only a relay and once you understand what a relay does the rest is easy. Just heavy(ish) duty wires from the battery to each relay, and then on to the headlights, not forgetting heavy(ish) duty earths to the headlights too. The relay's "trigger" terminal is fed from the wire that was feeding the headlights. The relay's earth wire does not have to be heavy duty. I would use 1 relay for the dip beams and another for the main beams. Tidy wiring, a ~15Amp fuse close to the battery, mount the relays sensibly (easy) and away you go.

[CovKid]

If its an early fusebox (ceramic fuses) I could write a 'how to'.

[dicey]

I came across this http://www.thesamba.com/vw/forum/viewto ... ay+upgrade on TheSamba before.
I havent read through it yet though.

[CovKid]

I wouldn't follow the Samba one entirely. The way its been done there it might take the load off the lighting switch but it'll do zilch for brightness of the lights unless the supply cable is increased too.

There are basically two stages:

1) Provide adequately rated cable for the relays from the battery, or an upgraded cable from the battery - not just back into fusebox.
2) Fit relays
3) Provide equally good earths.

[ghost123uk]

There are basically two stages:

1) Provide adequately rated cable for the relays from the battery, or an upgraded cable from the battery - not just back into fusebox.
2) Fit relays
3) Provide equally good earths.

I wouldn't trust him ^^^ - he can't count

[CovKid]

I added the 'earth' bit as its just as important. Make that three then.

[California Dreamin]

In response to the original question.
Most of what is there regarding the full wiring mod is what I've written.
At the time I didn't want to be so pretentious as to presume the way I did mine was necessarily the only way it can be done. I stopped short of writing a giude because no one way is the 'right way'.
However,
In my opinion....using the existing wiring as the 'switching' for the relays, then running two heavy feeds straight off the starter battery (petrol engined vehicles with the starter battery up front...and different for a diesel) leaves the original wiring untouched. Making a new earth post behind each lamp and then keeping the wires short as well as overating them by some margin. All this ensures minimal voltage drop and the brightest of headlamps.

Two heavy duty fuse holders next to the battery (15 amp fuses for single light)
3 metres of 25 amp twin core cable
2 standard make and break 30 amp relays (buy quality as there are some very cheap nasty ones out there)
All weather electrical box (to mount the relays in)
2 new 3 terminal headlamp bulb sockets (the ones that push on the H4 bulbs)
1 male 3 terminal socket (to push into the old offside H4 socket to get the switching signal)
Various terminals/bolts/shrink wrap.


Martin

Martin

[marlinowner]

It occurs to me that you could keep the original wiring connected to the lights as well, then if a relay packs up the light will stay on, back in it's preupgrade state.

[CovKid]

Far more likely a bulb would go rather than a relay, plus the sidelights are there to help mark that side should a headlight bulb blow, and they're independent of the relays. If you did retain the original wiring the load would be back on the lightswitch surely.

[marlinowner]

The thing is if the relay fails, or the fuse, then you lose both lights, although I agree its not very likely. I have spotted a flaw in my idea though. There wouldn't be any extra load on the switch, but once the relay was energised then it wouldn't switch off when the switch was opened...

[itchyfeet]

At the time I didn't want to be so pretentious as to presume the way I did mine was necessarily the only way it can be done. I stopped short of writing a giude

Nobody thinks a guide is pretentious or the only way, people love to read about how you did it.

[California Dreamin]

The thing is if the relay fails, or the fuse, then you lose both lights, although I agree its not very likely..

And of course you missed the 'full redundancy' of the wiring diagram. Two relays, two completely separate circuits. There is of course a chance of loosing Dip or Full beam but the chances of loosing both at the same time are extremely remote.....This was an early modification, made to the diagram (thanks to Bren, 1664) and makes complete sense.

Martin