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MGB Stupidity.

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WillR

WillR

Jedi Warrior
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Got the B running and as my temp gage decided to work i wanted to see how the cooling system was functioning sense i just got it put together last night and topped off the fluid today. ran fine fans kicked on when they should. When the heater fan decided to work it pushed hotter air that i have ever felt. Good news. The stupidity happened when the car started to idle to slow it died. I looked around at a few things and went in to eat some lunch. when i came out i noticed i left the key on. Now im getting no spark. turns over fine plugs wet. Cleaned the points off with emery board still nothing. What damage did i do when i was so close to taking my first shake down? :wall:
 
With points I wouldn't expect leaving the key on to cause any issues -- can if you're running a Pertronix electronic ignition. Is the '78 straight points or had they switched to some sort of electronic ignition by then? Can't remember...
 
they switched by my year to a pointless ignition, but i went back to a points set by advanced dist. im worried i burnt my points and condenser.
 
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after some reading online im thinking by leaving my coil powered up i cooked it. i found a fast way to test it but im having trouble rallying myself to get back to the drive way. Late tonight or tomorrow.
 
Sometimes it's best to take an evening off and have a bit of your favorite beverage after you have a "moment" with the car -- has saved me from doing worse harm in the past!

Deep breath, everything is fixable on these cars, even the things you break yourself. I know that all to well. :grin:
 
You won't damage the points or condenser by leaving the power on. Maybe you could damage the coil, but I'd expect the coil to be designed to take it. 'Course, if you had a low-resistance (6 volt) coil, maybe that would do it.

At this point, the name of the game is SYSTEMATIC TROUBLESHOOTING! If you're not getting spark, be sure you have the right primary resistance at the coil, voltage at all points where you should have it, and so on.
 
i hate to admit it, i have to walk away at least for tonight. I just feel pushed to finished as i would like to get home to my wife and this cars "reliability" is all that stands between her and I.
 
Leaving the ignition on for long periods of time will damage both the points (if they are closed, taking the temper out of the spring) and the coil as the result of over heating. Both of these results will occur only if the points are closed when the ignition is left on (as the points are closed most of the time, it is a good chance that damage has occurred). The capacitor (condenser) will not be harmed by constant voltage applied to it with the ignition on.
Cheers,
 
well at least the condenser is fine. ill get out in a few moments to test the other things. thanks for the direction.
 
well the coil is pushing out a spark. any clear way of testing the points? moss has them for 8 bucks. napa for twenty. moss even comes with a new condenser
 
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Coil overheat, ballast resistor fried, points turned blue.
Yeah, you leave the key on with points closed, you can do a lot of minor damage.
Seen it a LOT over the decades.

With a piece of cardboard holding the points open, you have battery power at the wire to the points with key on?
Usually blues the point contacts, takes the tension out of the spring, and if it has a plastic insulator where the wires connect, melts that, too.

Dave
 
i dont have power at the wire to the points with key on. i put in a new set of points and a new coil. i slid in the cardboard and checked for power both at the wires inside the distributer, and at the connection point right on the out side. however this is negative earth, no power is coming out of the coil to the points. I took off my old coil one side at a time just to make sure i put it back together right.
 
as much as i hate taking any of my vehicles to a shop, I fear im out of options at this point. Iwas hoping to start driving late this week. I cant even get a spark right now.
 
Not an expert by any means - and I know you said it turned over, but, did you drain the battery?

and, or,

can you check for continuity with the actual wires? could you have burned through one?
 
Okay...no power at the coil with key on. NOT the points or coil if you have no power on either coil primary wire.
If you have power to one side of the coil, disconnect the wire to the distributor and then, with it safely out of the way, key on, check for power on the end of that wire.
If you have power, you may have mis-assembled the points.
Seen it done.
If any of the bits are on the ground side of the insulator, it will act like the points are closed, and there will be no power out.

Now, do you have power on either of the coil primary wires?
If so, with the wire to the distributor removed (and you can do this at the distributor...only reason I have you check ay the end it to make sure that wire has not failed) do you have power at the end? Do you have power at the other end where it connects to the coil?

Report back and we'll go from there.

Dave
 
Good, Dave! Possibility that the points are in there with the trigger leg grounded by mistake. Too easy to do. Will, the two leads attaching at the post in the dizzy where the pivot pin for the points assembly is, MUST NOT be allowed to attach to a ground. They should have a fiber washer or other non-conductive insulator (plastic, nylon, etc.) keeping them connected to the moving side of the points but not to a ground path.
 
I have left a trickle charger on it to keep the battery up. I will check to see if I burned any of my wires. that easy enough to fix. There was a wire that was grounding, just inside the distributor the beginning of the wire had been touching. I have no power going to the coil. This seems to be where my knowledge is severely lacking. It is a negative earth car. Wire to the points is the negative side of the coil. How does the power get to the points?
 
This may help:

 
Mickey, thank you for keeping an eye on this post. I sat and re watched that a few time over yesterday and it cleared a lot up for me. the only thing i can think is my distributor SHOULD be going to the positive side of the coil. i know power is going to the coil, its just not getting to the distributor.
 
Unless you have a positive ground system, the negative terminal of the coil is the one you hook to the distributor. My money's on Doc's and Dave's assertions that you've a ground problem. That means that even though the cam is separating the points, the short keeps the circuit from breaking.
 
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