MG Car Repair: electrics, dual gauge, temp gauge

Question
QUESTION: Hi
I recently fitted anew dual gauge as the temp gauge was not working. While upside down under the dash I took the opportunity to 'tidy' up some wiring. I was careful to ensure I re-plugged where it came from. After this I drove the car - new gauge fine - but car would not stop when I turned off the ignition but did when I turned off the lights! I then noticed that even with the ignition off - if I turned the light switch on the alternator light comes on and petrol pump ticks. Any ideas what i might have done??

ANSWER: Hi Tim,
What kind of car is this?
Howard

---------- FOLLOW-UP ----------

QUESTION: sorry

the car is a 1970 MGBGT

Tim

Answer
Hi Tim,
You evidently were not careful enough when plugging wires back together as it sounds like you have plugged one of the "IGN" wires into a light circuit. The "IGN" light is not an ignition light but is powered by the ignition circuit. The light is a "Charge" light. The power from the "Ignition on" circuit goes through the bulb to the Alternator to excite the alternator into starting to charge. As soon as the alternator starts to charge the exciter wire turns into a positive and now with a positive on both sides of the "IGN" light, it goes out.
My guess is that you plugged one of those wires in the wrong socket.
Lucas gets a lot of jokes but Lucas is very good about color codes so go back under the dash and check color codes as compared to your wiring diagram.
If you don't have a diagram let me know and I will post one on my web site for you to copy.
Howard