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MG MGB Technical - Ignition Probelm

I've read the other 'can't get it started' threads, and I'm down to the following problem:

I'm not getting any spark. I've got a new coil, new points, and new condenser. Using a voltage tester, I've got 12V going into the '+' side of the coil via the white wire, but only about 1 volt on the '-' side via the white/black wire when the points are closed. When I open the points manually, I get no spark from the HT lead to the block (even holding it very close to the block).

Aren't I supposed to get 12 volts going out the '-' side with the points closed? What could I be doing wrong here? Any advice is appreciated!
Brian LaVoie

I believe zero volts would be better with the points closed.
George B.

Brian. You should have about eight volts coming from the negative terminal of your coil. With the point closed, you should have the input voltage flowing through the coil, down the wire to the distributor, then to the points, through the points contacts (when closed) and grounding to the base plate to the distributor body, thence the block. This makes your circuit. One thing that comes immediately to mind is the fact that Brit points sets are connected differently than their US counterparts. With the US points set, you remove the nut on the stud and attach the coil wire and condensor to it. With a Brit points set, you remove the nut and the plastic spacer, install the coil and condensor wires on the plastic spacer, then install the wires and spacer on the stud and secure with the nut. The wires must make contact with the spring arm and must not make contact with the stud itself or it will ground out and you will get no spark. You might try this and see what you get. But, the one volt reading puzzles me. A note to Paul Hunt is probably in order. Les
Les Bengtson

Les,

He said he was getting 1 volt with points closed, it should be zero. The eight volts should be seen at the + connection when the points are closed, 12 when open on a static test.
George B.

Unless you have a ballast resistor you should read 12 volts on the plus side of the coil with
points open or closed. The negative coil terminal should be zero volts with the points closed.
What happens to the voltage on the negative terminal when you open the points manually?
If it is still around 1 volt you probably have incorrectly assembled the contact connector to
the coil and condensor wires. Look at the contact spring and plastic spacer. The components
have to be assembled so that there is no ground path except through the contacts as Les
suggested. Clifton
Clifton Gordon

I appreciate your responses! After I wrote, I found my Haynes manual and followed the tests they recommend. I pulled out the distributor (which was from a later car) and replaced it with the distributor from my '69. I replaced the condensor at the same time, making sure that there was an insulator on the bottom of the stud, followed by the spring, then the condensor, then the LT lead, the second insulator, and the nut. I'll check it again tomorrow, but I could swear it's correct. From the tests with my voltmeter, it looks to me like I'm grounding to the block with the points open or closed, but I can't figure out how. The next thing I'm going to try is bypassing the harness entirely from the coil to the dizzy. I'm wondering if I have a short in the harness itself. I'm baffled, frankly.

Any other thoughts out there? I'll let y'all know what I find tomorrow. After having paid too much and spent too long working, it would be a real morale booster to hear the thing run, even if briefly...
Brian LaVoie

Sorry, I assumed negative ground and ballasted, no year stated. Isolate the points from the rest of the wiring and check for continuity between the point contacts with the points open. You have an assembly problem if you get continuity, not a harness problem.
George B.

Just wanted to let y'all know it turned out to be a short circuit to ground in the distributor. Took it apart, reassembled and got spark.

I just heard it run for the first time since I bought it almost two months ago - way cool! Supposedly, this is the first time it has run in over 10 years. At high idle, I had 50 lbs of oil pressure! (High-flow oil pump, or so I'm told by the PO.)

Unfortunately, I've discovered that I need a new heater valve and new seals around the tappet covers. Not to mention an interior! It'll be a while yet, but sure is nice to hear it run...
Brian

This thread was discussed between 11/06/2002 and 13/06/2002

MG MGB Technical index

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