I want to fit relays to my headlights to get better light from them.
However I forsee a problem with the dim/dip in that the current for the dim will trigger the relay to put dip beam on when I select side lights.
Do I have to have dim/dip for the MOT and if so is there a way to still have dim with the side lights or how do I remove the dim/dip set-up (I know it's the little box behind the dash but I assume that I'll need to wire it out somehow).
TIA
Mo

For MOT purposes you have to be able to select side lights, dip headlamp, and high beam.
If you want to fit relays for dip and high beam - then use two relays. I assume you would use the original switches still? If so, they would still keep the three circuits seperate from each other.


Les.

I've got a wiring loom on my 90 like this (It's an ARB headlight loom, but dead easy to copy)

I don't have the dim-dip (where the headlights are on 1/10th brightness with the sidelights) as it was impossible (without getting into electronic hassle!) to wire up.

the loom is quite easy to make.... 3 relays (spotlight type ones). main feed from the battery into the loom. one relay operates bothe headlights on dipped beam, the other two operate them for main beam. just connect the "feed" to the relay coils into the existing headlight loom (my loom came with a plug that just fitted into the plug that goes on the back of the headlight bulb), so when you're on "dipped" bead, the dipped feed will energise the dipped relay, and on main beam, the dipped will de-energise, and the main beam feed will operate the two other relays.

See what you mean about 'dim'. Sorry


Les.

Yep Les, I understand that. But the dim headlight on sidelights uses the dip wiring.
If I use the original dip wiring to trigger the new dip relay, then when I turn the side lights on, the current for the dim headlight will trigger the relay and turn on dipped lights.
So I suppose the real questions are : 1) on an '86 90, would the 2 white sidelights alone (without the dim headlight) meet the mot requirements ? and
2) what's the best way to wire out the dim/dip box behind the dash ?

Dim is not an MOT requirement. Sidelights are though. They are supposed to be 5w I think, but I use indicator bulbs in place of them as I feel that 5w is too weak. I've never had an MOT problem with brighter side lights.


Les.

Thanks Les. Did you up the wiring or is standard up to the job of using 21w bulbs ?
Thanks Jamie, I'm a bit puzzled though why I'd need 2 relays for main beam ! Would this be for if you are using 100w bulbs ?

Mo

Wires for indicators and sidelights are the same size, so no problem with it on that side.


Les.

I would use two relays for both dipped and main beam, 4 in total. Other wise if the dipped relay failed you'd end up with no dipped beam.

Mo,

You can just unplug the Dip box inside the dash - and the headlights will continue to work in the manor you want (without the 6v dip feed)

Si

"I would...." ... but have you and did you? Good idea but do manufacturers have this sort of redundancy? Is it worth the extra complexity, cost and weight(!) to have 2 more relays? Why not carry one spare or rewire the main for the dipped to allow you to get home? How often have you come across a relay dying (that has not been subjected to its eyballs in muddy water )

Just wondering

Just what i was going to say! or unplug the resistor thats mounted in the RH wing (just past where the radio aerial usually lives). when these resistors burn out you lose the dim-dip bit too.




Thats the way the loom came. as it's American, i suspect they have 10000w bulbs running Dr Pepper can dispensors on each wing, along with beer coolers, so they need all the amperage they can get!

seriously though, if you're running 100+w bulbs on each headlight, having an individual relay can't be a bad thing. it certainly made my lights "whiter" instead of that dull "yellow" glow you get.

The only "down" side i've found... if the main fuse blows for the light loom... you lose ALL your headlights!

Lot of modern day cars have a seperate relay for each lamp. The weight is negligible though. I wired spot lamps in pairs on catflap, not too sure what I would do an the standard lights. Individual relays does make a lot of sense to me, but if a bulb blows - the other will still work won't it? so it would be only a relay failure that would kill everything.


Les.

No i haven't as I haven't wired relays into my lights, but if I did I would. I think it's worth the extra effort.

As Les said, yes manufacturers do have this level of redundancy. My 90 as standard from the factory (with no relays) has seperate circuits with a fuse for each main and dipped head light, ie 4 fuses.

It is the same reasoning as why trailer electrics have seperate circuits for LH and RH tail lights.

I tried this in mine - and the lenses, being plastic, melted. IIRC, Les has military types and Mo has NAS types and these may be able to take the heat - but my standard ones would not!

Chris

Thank you Gentlemen. I had planned on a single relay for each of dipped and high beam for simplicity but I can see the benefits of redundancy, however, how often does a modern relay fail ? Would this really be necessary ?
I'll try a couple of 21w bulbs and feed back to you

Mo

I thought that as well, but thinking more about it, modern cars are so complex that it would be next to impossible to tonk something up to get you home, unlike on a series.

about the bulbs interesting .... 21 W is ok for indictors since they are on for about 1/2 the time = 10 W; must have a look sometime at my side lamps - but I have a gut feeling they are 5 W.

Sidelights are normally 5watt, 1989 road vehicle lighting regs state Must be white, no requirement on wattage but must be visible from a reasonable distance.

I had 21w bulbs in my sidelights but gave up and went back to 5w. The lens covers don't seal too well & slightest drip of water hits the bulb & explodes it. Thought about sealing them up with silicone but reckoned they'd overheat due to lack of airflow

5w bulbs run much cooler so cope with dunking.