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MG MGB Technical - A new page added to my site...

I have added a Misc. Electrical page to my website, Muenchausen's Garage, covering at this point, installation of the Audiovox CCS-100 cruise control and the addition of headlamp relays. Go to http://www.cibolas7.net/30105.html for this new information. Thanks.
Bob Muenchausen

Bob

Nice, and useful, addition.

Thanks

Larry
Larry Hallanger

Thanks, Larry. I just put it up and it will be updated as I receive feedback from folks. All feedback is welcomed as there seems to always be things I forget or perhaps a better way of stating something that is easier to understand for all who visit the site.
Bob Muenchausen

Bob; Great information. Thanks for posting. I have the same setup on my headlight relays, the relays are on the inner fender ahead of the radiator and I have mounted a Lucas fuse box near the coil. I can send photos if you would like to have them.

Clifton
Clifton Gordon

Personally I added relays and fuses *behind* the radiator shroud, to give them some protection. I've had relay spades rot off before.
Paul Hunt 2

Bob this is the exact same system, including fuse panel but I also added horns and cooling fan relays and mounted it all on the back of the rad support above the oil cooler lines.

Do I correctly understand that your relays are double pole double throw? If yes where did you find them, they are truly scarce up here in Canada.

Norm Peacey

Norm Peacey

Clifton:
If you have some photos, please send them! I may include them on the site if you don't mind. Credit to you will there too.

Paul:
I recently updated this page after some discussion with some other folks. I got a very good link to the British V8 site for their discussion of 4 fuses (which I believe you also advocated) and will now have to modify my own install for the two additional fuses. It does make sense.

Norm:
Sounds like you did something more like Paul did. I mounted my relays where I did because I felt that inside the engine compartment, behind the radiator diaphram but on the fender (on a 68, there is plenty of room, on some other years there is not) was adequate protection from the elements. Some folks have advocated putting the relays up under the latch plate because of its proximity to the headlamp connections. Not a bad idea either IF you do an decent job of enclosing the relays and fuses in a sealed box. As I indicate on my page, Dan Masters has an excellent solution already made up with instructions for wiring it into your electrical system with 4 fuses ~ a safer method for many reasons.

And No, I did not use double pole double throw relays. The relays I used are single pole, single throw. Each pair of filaments (2 high beam filaments, 2 low beam)uses one single pole relay controlling one power lead to each pair.

By today's standards you can use one single pole for each beam's filament and each having a fuse to protect it or you could use one double pole, double throw relay per beam with one fuse for each filament for a total of 4. The fuses would simply be inline on the line from each pole of that beam's relay to the individual filament it fed. Two double pole, double throw relays cuts down the number to use, but that is not an absolute necessity. To my mind it just depends how much space you have, and where you want to place your fuses. Certainly, using two double pole units is more efficient ~ until one of them dies (which is not often). When that happens, however, you end up in the same boat as I do with just two single pole relays ~ that whole beam goes dead.

If you want to use double pole, double throw relays, I would suggest that you will find it easier to procure them online from a specialty automotive electrical or industrial supplier than in most chain auto stores.
Bob Muenchausen

A double-pole, double throw relay would supply all four filaments, i.e. only *one* relay is needed. With winding failure you would lose the high (presumably) beam both sides, which would also be the case if you used a single-pole double throw relay and had either winding *or* the high beam contact failure. However if you had the common fail on a single-pole, double-throw relay then you could lose both beams both sides, so this is obviously to be avoided. Double-pole single-throw needs two relays, but whilst a winding failure will cause failure of that beam both sides, any single contact failure will only affect one beam one side. That is *slightly* more robust than using two single-pole, single-throw relays where a single contact failure will affect both sides of the affected beam. In all case there would still be a need for four fuses i.e. one per filament.
Paul Hunt 2

As far as I know, there are only three types of automotive style "ice cube" relays available: single pole single throw, single pole double throw, and single pole single throw with two output terminals. In the world of industrial relays, the sky's the limit. I have a 12 volt relay in my spares bin that is a 12 pole double throw. I have no idea where it came from, or why I have it, but it is not really suited for use in an automobile. I guess it could be used but mounting it would be a problem.
If you want to use one of these relays to replace a Lucas relay, use the following equivalencies:
W1 = 85 = coil input (positive or ground)
W2 = 86 = coil input (ground or positive)
C1 = 30 = power input
C2 = 87 = power output
If your Lucas relay has a C4 contact, I know of no ice box relay that will replace it. The closest you can come would be a single pole single throw with two output terminals, but be careful before using this type. The two output terminals, 87, are connected together in these relays, and bot are then connected to the 30 pin when the relay is energized. With the Lucas relays having a C4 contact, the C2 and the C4 contacts are isolated from each other until the relay is energized, and then both are connected to the C1 pin.
I haven't seen a Lucas single pole double throw relay, so I can't comment on the equivalency for them. I'm sure there are some, but I haven't seen one.
When wiring up to an ice cube relay, pins 85 and 86 are interchangeable - it doesn't matter which is wired which way. The same is true of the Lucas W1 and W2.
The same is true of pins 30 and 87, or pins C1 and C2.
For a picture of all this, see: As far as I know, there are only three types of automotive style "ice cube" relays available: single pole single throw, single pole double throw, and single pole single throw with two output terminals. In the world of industrial relays, the sky's the limit. I have a 12 volt relay in my spares bin that is a 12 pole double throw. I have no idea where it came from, or why I have it, but it is not really suited for use in an automobile. I guess it could be used but mounting it would be a problem.
If you want to use one of these relays to replace a Lucas relay, use the following equivalencies:
W1 = 85 = coil input (positive or ground)
W2 = 86 = coil input (ground or positive)
C1 = 30 = power input
C2 = 87 = power output
If your Lucas relay has a C4 contact, I know of no ice box relay that will replace it. The closest you can come would be a single pole single throw with two output terminals, but be careful before using this type. The two output terminals, 87, are connected together in these relays, and bot are then connected to the 30 pin when the relay is energized. With the Lucas relays having a C4 contact, the C2 and the C4 contacts are isolated from each other until the relay is energized, and then both are connected to the C1 pin.
I haven't seen a Lucas single pole double throw relay, so I can't comment on the equivalency for them. I'm sure there are some, but I haven't seen one.
When wiring up to an ice cube relay, pins 85 and 86 are interchangeable - it doesn't matter which is wired which way. The same is true of the Lucas W1 and W2.
The same is true of pins 30 and 87, or pins C1 and C2.
For a picture of all this, see: http://As far as I know, there are only three types of automotive style "ice cube" relays available: single pole single throw, single pole double throw, and single pole single throw with two output terminals. In the world of industrial relays, the sky's the limit. I have a 12 volt relay in my spares bin that is a 12 pole double throw. I have no idea where it came from, or why I have it, but it is not really suited for use in an automobile. I guess it could be used but mounting it would be a problem.
If you want to use one of these relays to replace a Lucas relay, use the following equivalencies:
W1 = 85 = coil input (positive or ground)
W2 = 86 = coil input (ground or positive)
C1 = 30 = power input
C2 = 87 = power output
If your Lucas relay has a C4 contact, I know of no ice box relay that will replace it. The closest you can come would be a single pole single throw with two output terminals, but be careful before using this type. The two output terminals, 87, are connected together in these relays, and bot are then connected to the 30 pin when the relay is energized. With the Lucas relays having a C4 contact, the C2 and the C4 contacts are isolated from each other until the relay is energized, and then both are connected to the C1 pin.
I haven't seen a Lucas single pole double throw relay, so I can't comment on the equivalency for them. I'm sure there are some, but I haven't seen one.
When wiring up to an ice cube relay, pins 85 and 86 are interchangeable - it doesn't matter which is wired which way. The same is true of the Lucas W1 and W2.
The same is true of pins 30 and 87, or pins C1 and C2.
For a picture of all this, see: http://www.advanceautowire.com/techtips/relay types.jpg

Bob, If you think it worthwhile, feel free to add this to your website.
Dan Masters

Well, I screwed that up, didn't I? My apologies!

What I meant to say was:

As far as I know, there are only three types of automotive style "ice cube" relays available: single pole single throw, single pole double throw, and single pole single throw with two output terminals. In the world of industrial relays, the sky's the limit. I have a 12 volt relay in my spares bin that is a 12 pole double throw. I have no idea where it came from, or why I have it, but it is not really suited for use in an automobile. I guess it could be used but mounting it would be a problem.

If you want to use one of these relays to replace a Lucas relay, use the following equivalencies:

W1 = 85 = coil input (positive or ground)
W2 = 86 = coil input (ground or positive)
C1 = 30 = power input
C2 = 87 = power output

If your Lucas relay has a C4 contact, I know of no ice box relay that will replace it. The closest you can come would be a single pole single throw with two output terminals, but be careful before using this type. The two output terminals, 87, are connected together in these relays, and bot are then connected to the 30 pin when the relay is energized. With the Lucas relays having a C4 contact, the C2 and the C4 contacts are isolated from each other until the relay is energized, and then both are connected to the C1 pin.

I haven't seen a Lucas single pole double throw relay, so I can't comment on the equivalency for them. I'm sure there are some, but I haven't seen one.

When wiring up to an ice cube relay, pins 85 and 86 are interchangeable - it doesn't matter which is wired which way. The same is true of the Lucas W1 and W2.

The same is true of pins 30 and 87, or pins C1 and C2.

For a picture of all this, see: http://www.advanceautowire.com/techtips/relay types.jpg
Dan Masters

One more try!

http://www.advanceautowire.com/techtips/relay%20types.jpg
Dan Masters

http://www.advanceautowire.com/techtips/relaytypes.jpg
Dan Masters

We're definitely lauging with you, not at you on this one, Dan. I've been working in computers since punched card days (1972) and the dang things still cause my hair to hurt. This is good info.

R.
Rick Stevens

Yeah, welcome to the club on this one, Dan. I seem to be going through that with this page. ;-)

Thanks Dan, for permission to use your comments! I will be more likely to just add a link to your relay discussion and then see if I need your discussion above as well. I hate reinventing the wheel when there are better discussions than my own to lead people to. I put up my site (the whole thing) to post things in a convenient form that most other sites did not address and to help folks find things that could help them easier. But if there is already a good site on a topic out there, then I am going to direct folks to those sites. I think most folks just stray across my site, anyway, so I see it as just one of many places to pass along info. when a Google search pulls it up on somebody's PC screen.

Now, if anyone knows of a really good site WITH REALLY GOOD PHOTOS on the topic of how to learn to solder, let me know. I blew a whole afternoon last weekend trying to find one, but probably just don't know how to narrow the searches well enough.

As I have said elsewhere, after teaching HS students in tech stuff, I have found that they, and most people, learn more easily if there are multiple paths for their understanding. Some of us are Right Brained, some Left, some visually oriented, tactily oriented, verbally oriented, etc., so to try to get things across, I really like to be able to offer photos rather than drawings, so that they can see an actual joint and give some real world meaning to things like "cold solder joint", "good solder joint", "shiny surface". Most folks will get the idea just from some of the great sites I saw, but not as many, IMO, as would have had there been a few photos along with the excellent verbal descriptions I saw.
Bob Muenchausen

BTW, Paul, thanks for straighening out my misinformation on the Double Pole, Double throw relays. I was thinking of the double pole single throw. I need a refresher course, obviously.
Bob Muenchausen

This thread was discussed between 11/10/2006 and 21/10/2006

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