Headlight relays

[Robbie693]

Hi,

I want to do the relay thing in order to cure the lights cutting out problem. Thing is, I am an electrical dunce!

I have been reading this: http://www.danielsternlighting.com/tech/relays/relays.html

I think I understand what to do but it mentions a few things I could do with some advise on.

1. First off, the article suggests 12 gauge wiring (4.0mm sq), The closest I can find is 4.5mm wire - Will this be too heavy/stiff? Do I really need that heavy a wire for 60/55W H4 bulbs?

2. It also rekons that to accomodate this bigger wire I'll probably need new bulb holders - Will that be the case and where can I get them?

3. I intend to take the power from the starter solenoid and, as recommended by the article, I am going to fit fuses - what rating will I need?

Can anyone who has done this job share their know-how and explain what you did please..

Thanks in advance

[RotoFlexible]

I fitted standard sealed-beam halogens (I think 60/40 or 50/40, but in the same ballpark as your H4s) a couple of years ago.

1. I used 28 strand (14ga) as recommended by British Wiring and used by them in their headlight pigtails. It's been fine. It's rated to carry 17.5 amps which is more than enough (see below). 12ga seems like overkill unless you are planning to run real flamethrowers.

2. Can't help you on the H4 bulbholders since I don't use H4s but if you are using 14ga the question may be moot.

3. Assuming you fuse the high- and low-beam circuits separately (which is what I did): 60W x 2 = 120W for the high beams. That means the circuit is carrying about 10A (120W/12V). I used 15A fuses for both circuits - comfortably above the current needed by the headlights, and below the carrying capacity of the wire. They haven't blown yet

[Robbie693]

Thanks very much Andrew.

Robbie

[RotoFlexible]

(Reaching for the shift lever...)

Just to clarify, I made these modifications on an Elan S2, which had no relays to begin with. I wanted to maintain a reasonably original appearance under the bonnet so I placed the relays under the dash and fed the low and high beams with a single 28-strand wire each, as in the original harness. But - in one pass, I replaced the ancient sealed-beam units with halogen sealed-beams, replaced all the wires, replaced the connectors, and added relays with modern fuses, fed directly from the starter solenoid. I got rid of the voltage drops across the light switch and all the old connectors. The cumulative effect was a spectacular improvement, but I can't say how much was due to the relays, how much to the connectors, and how much to the new sealed-beams.

Stern's excellent article outlines an optimum solution if you want to be absolutely sure the lights are getting all the volts they can, especially for high-power units. If you aren't concerned about placing relays under the bonnet (preferably right up in the nose, close to the headlights) then that's the way to go. Run one heavy-gauge wire from the power source to the relays to minimize the drop over that (relatively) long run. I still think you can run 14ga from the relays to the headlights esp. if you use the relays with two output terminals and run individual wires to each light. This is bound to be better than the approach I used, but how much better is hard to say.

[Robbie693]

Thanks again Andrew,

I think I'll put two twin make and break relays in the nose, fed by 14ga wire from the solenoid (fused in line) and then run 14ga to the headlights, if it will fit into the bulb sockets and I can get them apart. I can't remember how the wires are fixed in the bulb holders, hopefully they are just spade teminals.

Does that sound right?

[bcmc33]

Robbie,

You don't include your location or car details so it's difficult to give proper and good answers to your questions.

Regarding the H4 bulb holder - these are cheap items that can be obtained from many sources. The bulb holder comes with cable tails of the correct gauge, so this will tell you what to use for a rewire.

If you're in the UK then a good reliable source link is:

http://www.vehicle-wiring-products.eu/V ... mepage.php

This company is a reliable next-day delivery outfit and can supply all the cables (gauge & colour) plus relays etc..

I?m guessing you have an old car, pre-relay model, so for a circuit use the S4 diagram that?s on the system here somewhere.

And fuses - what's wrong with the fuse box........that?s what it's for.

[RotoFlexible]

Thanks again Andrew,

I think I'll put two twin make and break relays in the nose, fed by 14ga wire from the solenoid (fused in line) and then run 14ga to the headlights, if it will fit into the bulb sockets and I can get them apart. I can't remember how the wires are fixed in the bulb holders, hopefully they are just spade terminals.

Does that sound right?

That sounds fine, except that I think I'd run 12ga from the solenoid to the relays, so you'll have it in the future if you need it. I don't know if the same socket that goes onto the back of a dual sealed-beam also works for an H4, but there is surely some socket that will work and will accept 14ga. (A socket like this is nothing more than a holder for female spade terminals that click into place.)

By the way - SOLDER EVERYTHING! I don't trust crimps except on bullet connectors (using the correct tool) and the sturdy (and un-Lucas-like) connectors with the red, blue or yellow plastic sleeves (again using the correct tool).

[Robbie693]

Sorry Brian - I am in the UK and it's for a Plus 2 S/130.

There are no relays as standard.

I've seen VWP and also Auto Electric Supplies. Both seem good and have all the bits I need.

By the way - SOLDER EVERYTHING!

Will do Andrew.

Thanks both

Robbie

[bcmc33]

I am of the solder brigade - and have been brought to task many times for being so.

It's true that soldered joints are less reliable in a vibration environment - that's why the auto and aero industries only use crimped connections. Having said that, I have less faith in my crimping abilities than soldering.

My current practice is to lightly solder the end of the cable, crimp the connector, and solder the connector and cable. Belt-and-braces, I know, but they seem to stay together better that way even though they are theoretically weaker to withstand vibration. To accommodate this potential weakness I do my best to position cables in a manner that minimises movement and vibration of the joint.

[RichardS]

Robbie

I am doing much the same thing in renovating some of the engine bay wiring.
I am going to fit fused relays which you can get from VWP- my Sprint has always had relays so it will be simple to swap the old relays for the fused ones - would be an option for you if you do not want to fit an extra fuse box.

My relays are mounted up under the nearside fibreglass bonnet rest where they are reasonably protected from the elements.

Richard

[Robbie693]

Brian -

Yes I am of the belts and braces approach too - Solder wire and then the terminal.

I found these 'Flying sockets' which look like a neat solution, should keep the elements out a bit better too:

http://www.autoelectricsupplies.co.uk/product/180


Thanks Richard,

I thought about that but haven't seen fused 5 blade relays, only 4 blade ones. I need 5 blade make and break so I can have one relay for the dip and another for the main.

I was going to fit inline fuses, I have seen some splash-proof ones that look good:

http://www.autoelectricsupplies.co.uk/product/297

[oldokie]

For crimpers, use either Klein or Thomas & Betts, I used them for years on electric fork trucks (hard rubber tyres, lots of vibration) with good result.

[Robbie693]

Hi,

Just making a list of the bits I need and need to know:

Is there a connection somewhere in the feed from the lamps/dip switch to the headlights?

Just wondering because I want to try and do it without butchering the existing loom. The feed from the switch must split in two at some point to go to the left and right light units(?), if there is a connector here then I can use that to connect to the relays.

Otherwise should I join both of the ends of the headlight wires together and connect to the relay at that point for the switch circuit, running my new, heavier, wire onto the headlights?

Hope this makes sense..

[handi_andi]

What I have done is to drive the relays directly from the feed that used to go to the headlights. There are two cables for both main beam and dipped that have bullet connectors on them in the nose cone. Hence you can jump a relay in there with the helpfully supplied ground as well if you want to. Also gives the benefit of there being a second feed available if one of them goes wrong, which has happened on mine. Although have to admit I can't remember where you are wanting to mount the relays so may not be that helpful sorry.

Andy

[handi_andi]

PS the circuit split happens at the main beam / dipped headlights relays and provides 2 feeds per circuit into the fuse box. So you could always jump into the circuit at the fuse box and just pull the connectors to isolate the existing lines down to the nose cone.