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MG MGB Technical - Where does this green wire go?

I have been working on my girlfriend's dad's 1980 MGB and we realized he is getting some form of current draw that kills his battery. We traced it down to the green wire off of the fuse box. It is on the #6 side of the fuse box, and the wire has 8 printed on the little black connector of it. I can't seem to find where it goes and I rather not butcher the wiring of his car to find it. If anyone can tell me where it goes I would really appreciate it. Thanks alot.

P.S. I have posted this on many other forums with out any answers so any help would be greatly appreciated!
firebirdjosh

FBJ. Probably the reason that you have gotten little response is that it is difficult to answer your question. The green wire, off the number 6 side of the fuse box, is the basic starting point for all of the green wire circuits. There are a number of them and it is impossible, especially without the ability to physically inspect and test the system, to tell you exactly where the problem lies. The green wire circuit is extensive. What you can do is have a copy of the wiring diagram copied at 300% expansion and laminated. Better yet, get the girlfriend's dad to do this and pay for it. At that point, you can use one of the water soluable markers to trace all of the green wire circuits. You would then need to detach all of the wires on that circuit and hook them up one at a time while using a test light, in series from the fuse box connection to the green wire output to see which are drawing current. When you find the one(s) that are drawing current, you can decide where your problem lies. Les
Les Bengtson

You can see a wiring diagram in color at this URL. Clifton
http://www.mgbexperience.com/view/index.php?service/wiring-later.jpg
Clifton Gordon

The number 6 connection on the fuse box is the correct place for green wires and *should* be fed through the associated fuse from the white/brown wire from the ignition rewlay, which should only be operated when the ignition is on, of course. Some of the green wires *do* present a load all the time (like to the instrument voltage stabiliser, tach, inlet manifold heater etc), which is why the white/brown has the 12v disconnected from it by the ignition relay to prevent these permanent loads from draining the battery. The problem is not the green wire itself, but something feeding 12v to it that shouldn't.

The fusebox has to be orientated the right way round as the top two fuses at the front are connected together for the parking lights, and if you get the fusebox the wrong way round the purple and green circuits end up being connected together, and the purple being always live connects power to the green circuit which will drain the battery.

However if all the greens *are* connected to 6 (and the purples to 8, reds to 2 and 4, brown to 7, white/browns to 5, and red/green to either 1 or 3) then the fusebox would appear to be the correct way round. As I say, there is no point tracing where the green wire goes, you have trace where the 12v is coming from that is obviously getting on to it.

Connect a voltmeter to the green connection of the fusebox. Turn the ignition on and you should see 12v. Turn it off and the 12v should disappear. If still present remove the fuse feeding the greens. Has it gone now? If so the voltage must be coming from the ignition relay, which is probably stuck on. This could be either because the relay itself is faulty, or possibly because you have a faulty diode in the alternator. So unplug the alternator and if the voltage now goes off the white/browns at the fusebox you know it is the alternator.
Paul Hunt

One source of a green wire that is often left disconnected and would run hot is the wire to the induction heater for the carb. This is often disconnected and left hanging when the car is converted to a weber unit or dual SU's from the single ZS carb.
Frank

Thanks guys! I get a few hundred mA of draw and when I disconnect the green wire (#8, not the other green wire on the same tab) it goes away. I have alot of ideas to try and the ignition relay is looking very promising.
firebirdjosh

You will always have some draw on this circuit as there are items that are always hot. Paul Hunt, a trained mechanical-electrical engineer, focused on the whole problem and found the most likely cause--there should not be power to that circuit unless the ignition switch is in the on position (or bad), or the relay is staying on and providing power when it should not. One of the advantages of going to a professional is, unlike those of us who are self taught, they tend to focus on the system rather than the exact problem. Les
Les Bengtson

Paul; Your comment about having the fuse box orientated the right way round reminded me to check a fuse box I added to my 74 a few weeks ago to see if is is orientated correctly. I added the fuse box to replace single fuses I have added in the engine compartment for lights and a cooling fan. The fuse box was pulled from a 71 GT parts car. I didn't remember any spades being tied together when I installed it. I looked today and it does not have a link connecting terminals 1 and 3. Since all wiring diagrams show them linked together I can assume the GT did not have the correct fuse box. I cannot check the wiring harness as I have disassembled it for spare wiring supplies. This is not a question, just a comment on another one of my oddball discoveries. Cheers, Clifton
Clifton Gordon

Clifton,

The link Paul mentions is on the back of the box, so it won't be visible unless you pull the box off the wall. A TR6 fuse box is identical except it doesn't have that link. A few TR6 guys have used an MGB box only to have problems with things being on that shouldn't be because of that link. From the front, the boxes are identical.
Dan Masters

Hi Dan: I did pull off the box and it has no link. I guess you answered my question about it's origin. It works fine for my application. Clifton
Clifton Gordon

This thread was discussed between 04/02/2004 and 06/02/2004

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