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MG MGB Technical - Best position for headlight relays?
|Just considering the options for where to place a block of 4 relays to handle the headlights etc. Two places seem obvious - the right inner wing near the front of the car, or under the bonnet locking platform in the centre. The latter appeals because the wire lengths to the various loads will be the same. A bit picky I know but having gone to the trouble of improving the volts at the lights they might as well be as high and as similar on both sides. |
Has anyone placed relays here before and what are the problems? Any ideas welcome.
|Four relays for headlights? Usually only two are required - one for dip and one for main, regardless of whether it is the main lighting or headlamp flasher being used. The output from each relay is sent via two fuses i.e. four fuses in all, one for each filament. One of my cars came with a relay on the slam panel and one of the spades corroded away. I mounted relays and fuses behind the radiator mounting panel where they are protected from the worst of the weather, give the most direct wiring, but still quite convenient to pick up the connectors by the right-hand headlight to operate the relays rather than cutting into wiring elsewhere. See http://www.mgb-stuff.org.uk/lights10.htm.|
Mounting relays in the middle might give each light an equal length of copper, but all you are doing is lengthening the run to the right-hand light which will have to come back across the car again which seems pointless. If it is going to be fractionally brighter (and I defy you to notice it) by having the right run shorter than the left then surely that is better.
|I mounted mine on the slam panel with an ali shield to keep the worst of the direct weather off them with a flip up plastic cover to be able to get to the fuses. (Made from the base and half of one face of a brake fluid container IIRC!|
|I would be grateful if anyone can give me a shopping list for this project. Is there a typical part # or anything for the relays I need? How about the gauge of wire used?|
thanks so much
|I placed mine on the RHS of the engine bay using a relay frame from Autosparks. Here is the link to the component.|
The relays I used are also from Autosparks:
Here are a couple of photos of the installation.
Using this frame is expensive but it keeps the relays out of the grime coming through the engine bay and if the relay should fail then it is an easy job to replace by removing the cover and puling out the dead one. However you would need to buy the proper crimp tool for the spade connectors supplied with the frame. This is a worthwhile purchase as it makes the best connections and means that you create cable terminations that look like the factory ones. I added the relay for my electric fan into this frame as well to make things neat.
For the wiring, I took a single brown cable from the starter terminal and wired this as a common power feed to the relay contacts. I then ran cables to the main and dip lamps from the other side of the contacts. Then I extended the cables that originally powered the lamps to the coil side of the relay so that the relays are activated by the current switchgear. I also wrapped these cables in loom tape, which I sealed with heatshrink at each end to stop it un-ravelling. This makes the added cables look like it is part of the normal loom.
I added one extra feature so that when the ignition is switched off the dip beams go off, leaving just the side lights on, if the main dash switch is in the on position as is the case on some modern cars. To achieve this I wired another relay, mounted behind the dashboard, with the coil powered from the white circuit to earth. Then the feed from the dash switch for the dip beam is wired through this relay’s contacts and then on to the coil of the relay mounted in the engine bay. In this case the relay is always powered when the ignition is on and the dash switch controls the lights. Once the ignition is switched off the dip beam is extinguished until the ignition is switched on again. Should the dash switch be in the on position the dip beam will illuminate or not if the dash switch is in the side or off position. My BMW works like this and I like the feature so I implemented it here.
Hope this helps.
|Thanks for the replies. Some good ideas here. The jury is still out on which way to go.|
Paul, the four relays are for lights + "etc", so two for the lights very much as you advise, two for other things. No, I won't be noticing the difference in output L to R for a few hundreds of millivolts, the point I make is that I might as well get the volts almost the same as it is in my power to do so. Presumably you mean the drop in the power feed will be more for the RHS than if the relays were on the RHS. Point taken, but the feed is a beefy 65/0.3 so I expect very little extra drop if I go this way. Lastly, where behind the radiator panel did you put the relays? Actually on the panel? I tried this yesterday and wasn't convinced I had enough room.
Richard, great reply. I hope you don't mind but I flicked through your other shots. Very nice. I was interested in the way you ran the temperature sensor pipework as I've always thought it one of the most untidy bits in the engine bay. Presumably you were still able to provide the 'coil' part that allows for engine movement? Do you have a shot of that end? Also, which crimper did you get in the end. I have two but neither appear suitable for the relay connectors from Autosparks (which is where I get my electrical bits as well).
|Richard - the link I gave above shows the location. I'm sorry but I still can't see the point of putting the relays near the middle of the slam panel simply to keep the lengths equal, it just means more wires snaking back and fore than there need to be.|
Vince - simple on/off relays are all you need, the basic 4-terminal type. These are available with and without integral fuses but get the ones without rather than using the ones with to supply both sides, as a single fuse failure will plunge you into darkness. They are often available in two or more current ratings, if you have a choice get the higher. Then you need a 4-fuse holder with fuses, the blade type make sense as you are going to need different ratings to the standard fuses anyway. I depends on headlamp wattage to some extent but I suggest 15 amps. I chose not to fit a main supply fuse, but if you decide to this should be 30 amps minimum. Bear in mind if this fails you lose both dipped and main beams, unless you have the presence of mind to use the headlamp flasher. Other than that it is just wire, bullet and spade connectors.
No worries, please look around. I found that when rebuilding, the pictures of others were very helpful in deciding how to rebuild mine. I hope these are of value to you.
The crimp tool I bought was the one on this link:
The Autospark site states which spade terminals it crimps; I would recommend it.
On the routing of the temperature capillary I agree with your point. I see photos in Original MGB and others, where the capillary is coiled near the fan heater motor or the distributor looking untidy. Have a look at this image:
There is enough length in the capillary for it to be routed as the photo shows. The “coil” that you mention to accommodate engine movement is created by the slight “U” bend shown in the lower left quarter of the photo. This is adequate for the engine movement experienced. In this picture you can see the whole route I adopted.
You might note the P clip holding the capillary to the radiator diaphragm; this is the ‘the rusty P clip’ that I felt I had to retain to for originality’s sake.
Hope this helps.
|Here's mine. Low beam, high beam, horn and overdrive.
|Richard, thanks again. I will spend some time going through your gallery. Many helpful tips there. I'm at the stage of first tentative steps of installation. See pic. Great fun but I seem to spend all my time wondering 'how' and 'where', particularly with pipes and cables.|
T, Now that's a good place. I was wondering about this only yesterday but got diverted into the 'box under the lock panel' method. I shall look again.
This looks great and should reward you with an excellent result, having done a heritage reshell please feel free to ask any questions, good luck.
|I've gone for the position suggested by T Aczel as it's easy access and can be made very tidy. The wiring is easier than the box under the lock panel, as Paul S always said it would be! It's a bit more exposed than behind the radiator panel but my intention is to avoid 'wet' as much as possible so any problems will be minimal.|
|Here's another view Richard, in case it helps. Sorry I don't seem to have a better photo|
|Thanks Tom. No problem with the photo. Looks almost the same as mine (now I've copied you!).|
|I didn't put mine all in one place. Headlights, high beam, and horn here:
|brake lights relay here:
|and heater blower motor relay here:
|Thnks D. Just out of curiosity why have you got your brake relay in the engine bay? I am putting mine in the boot to minimise the voltage drop to the rear lights caused by the long length of car wiring which, along with reducing the current switch by the brake sensor, I thought was one of the main reasons for using the relay method.|
|I put in the relay for the brake lights to reduce the current on the brake light switch. At the time I was not concerned with voltage to the lights.|
This thread was discussed between 19/10/2010 and 26/10/2010
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