MG Car Repair: 74 1\2 MG ignition mystery, puff of smoke, volt meter

Question
hi I just installed new ignition and switch. I was having strange shorting -out episodes for weeks and having to push start the car, and it would run fine until I shut it off, but then one day it quit while driving on highway. I Observed the old ignition giving off a very small puff of smoke shortly before this. The New switch and ignition worked well for a week, then same symptoms started. The loom wires under the dash at the switch connection get warm when car is running. ( normal? )  I checked and found that the connector with male female ends was little loose fitting, and made good by crimping. but ..still shorts out occasionally while driving ( engine stumbles ). I can induce a shorting out by wiggling the loom under the dash, but cannot locate any loose connector! I even smelled something burning briefly. Help! any suggestions?   thanks PW

Answer
Hi Paul,

Any time I received a car with an electrical problem I would try to isolate the problem into a small area. In your case you need to start by running a charging system test.

You will need a volt meter to run the test. Put the volt meter across the battery and read battery voltage. (12v +) then have someone start the engine and set the RPM at about 1500 RPM and read the voltage. It should read 13.8v to 14.5v but not more.

When you say you replaced the switch and the ignition what parts of the ignition did you replace?

Next, the answer to weather the wires should get warm and the answer is "NO". Any time any wire gets warm it means too much amperage is going through that wire for some reason and you need to identify that wire. What color was it and where was it?

What brand ignition system did you purchase?

If you are able to wriggle wires while the engine is running and it falters then you need to locate the bad connection or a broken wire inside of it's insulation.

I know this is difficult when you have a harness full of wires and it is in there so what you have to do is look at your wiring diagram and locate the power to the coil wire and get a piece of 14 gauge wire and run a bypass from the battery to the coil and make a test run to see if you can make it falter. Even though there are starting wires, there is only ONE wire that makes the ignition system operate.

If you don't have a diagram let me know and I will post one on my web site for you to copy and I will tell you which wire to bypass.

Howard