Hi Dumbargain,
First - Welcome to the Forum.
A lot of good advice. I don’t really have anything new to add. But as I had the same exact symptoms with my 78B about a year ago, I’d like to expound a little on what has already been said.
Here is what I would look at first.
1) Look at your Battery again. I don’t mean to beat a dead horse, but this is really important. Because you can’t really do much else until this is done. If you haven’t done so already take it down to a local Auto parts store to have it re-charged & load tested. This service is usually free and they will confirm if it’s really bad or not. Shouldn’t cost you anything except the money to replace your battery if it’s bad.
2) Check is your interconnections between the Battery, the Alternator and the Starter. Clean them off and retighten them to make sure you have a good connection. I know it sounds kind’a silly, but sometimes corrosion and/or grime at interconnecting points (terminals & connections) can build up & stifle your car’s charging circuit. Thus draining your battery or killing it out right. This is a simple thing to look at.
3) Check for bad wiring or cables. Another easy test - assuming that you have a voltmeter. Simply measure the resistance and/or the voltage drop between these connections. Ideally you should see readings as close to zero as possible (0.0Vs or 0.0 Ohms of resistance). High resistance wiring increases current loading and will diminish the ability of charging circuit.
4) Next you’ll need to look at your Alternator. Like your battery you can in most cases take it to an Auto Parts store to have it checked out. One sign that you have an Alternator problem is if your ignition light in the center of your dash comes on and stays on while you are driving. Normally this light doesn’t come on at all except when you start or turn off the car. If the Auto parts store can’t test it, you can do a simple test yourself with a voltmeter. After jumpstarting my B, I attached my voltmeter to battery terminals and observed that the voltage wouldn’t go over 12V at idle or under load. Nominal results for a good charging system should read about 13 to 14V for a low battery. In my case the Alternator turned out to be the problem with my MGB.
Anyway, most of these tests (or variations on them) can be found in the back of the MGB Moss Motors Catalog. Great reference book and cleanly laid out tests most of us can do in their garage. It describes these procedures as well as other tests you can do yourself in greater detail.
Good Luck!
[ 07-02-2003: Message edited by: Bret ]</p>
Hi Guest!
Hey - did you know if you click on the title of a thread it will take you to the first unread post since you last visited that thread?
but were afraid to ask: 
STOP!! Never post your email address in open forums. Bots can "harvest" your email! If you must share your email use a Private Message or use the 
smilie in place of the real @
Pretty Please - add it to our Events forum(s) and add to the calendar! >> 
