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MG Midget and Sprite Technical - ignition light--waxing and waning


Ignition warning light came on after a long hard mountain climb. The alternator (74 midget) has been checked by a competent shop and found to have nothing wrong with it. Connections to the alternator were good. When at idle, the red warning light is bright, dims a little when revving to higher rpms.

Anybody have any thoughts?

Thanks!
JM Morris

Does the light stay on with the key out, is the battry hot, does the headlights, radio, whippers get brietheter and faster when you apply the gas then dimm when the revs returns to idle.

Then agian it could be just a bad ground and an assocorry is draining the battry


Prop
Prop

JM. Get the alternator checked by another shop. If the light is on, it indicates an imbalance between the charging circuit and the battery.

Put a volt meter across the battery terminals and take a reading. Should be a minimum of 12.0V and may read as high as 13.0V. Then, take a reading with the probes touching the outside of the battery terminal clamps. You should have the same reading as you had when touching the probes to the battery terminals. If it is less, you need to clean the terminals and clamps and recheck.

Start the engine and run the engine up to about 1000 rpm. Check the system voltage which should read between 13.5 and 14.5 volts. If it does not, you have low output voltage causing the light to stay on.

The second thing which can cause the light to stay on is lack of output amps. This test, normally, has to be performed by a professional having the equipment to put the alternator under load. But, as a quick test, if the ignition warning light is glowing dimly (or is off) and comes on when you turn on the headlights and sound the horn, the alternator is not putting out sufficient amps to run the various systems and needs to be replaced.

If the alternator is fully functional, the only thing that can cause the ignition light to glow is the battery side wiring. Check out the wire going from the battery to the warning light for connection problems.

Les
Les Bengtson


Thanks, fellas. I'll give all of this a go Saturday and report back.
JM Morris



Thanks , Les,
I've printed that info and pasted it into my Haynes manual. Clear as a bell , even I could understand it.
Arthur Jessop

The alternator in my '68 Midget does exactly the same thing and has done for more than 10 years. My auto electrician told me that it is a blown diode, he said I could get it replaced or just put up with it. Over 10 years later, I'm still putting up with it!

One of these days I'll pull it out and get it repaired but there have been other priorities. If you can find an old time auto electrician, he should be able to repair it for you. Unfortunately, the auto electricians who repair things are a dying breed, now days they tend to just replace.

David
David JM

Mine '68 Midget with alternator does the samething periodically. Putting load on gets it to go out ie. headlights on.I just wiggle the conections on the alternator and the external regulator and it goes away.
Usually happens in wet weather.
Col.
c pearce

Check that the belt is tight enough?
Garyfrog


Update: I put the checked alternator back on the car. Fired it up--and no warning light. Thought all was fine. Took off on a trip. About 15 minutes into the trip, the light came back on. I turned around to head back, and about a minute later the light went out! Decided to chance it and continued the trip. The light continued to randomly come on and go out. At times, I could rev the engine and it would go out, but a few minutes later, come back on. Toward the end of the day, the light stayed off more.

I'm thinking this may be a heat related, intermittent contact problem. When there is a great deal of "heat soak" in the engine compartment (after a high speed spurt) the light seems to come on more. On the other hand, it sounds very similar to what David in Australia is experiencing. (The belt is plenty tight, and all wiring and connections are new--I have Advance Auto Wire's modern complete wiring system. Been running the car for a year with no problems til now).

I've taken a look at the alternator parts in the VB catalogue. It looks like the voltage regulator has leads that attach via screw connections. So if there is a slightly loose screw, maybe heat expansion can create a break in continuity?

Next step will be to follow Les's diagnostic procedures to see if the problem can be narrowed further. By the way--thanks loads, Les. Outstanding description of the diagnostic procedure.
JM Morris

>>> Thread: ignition light--waxing and waning <<<

Every time I wax my car, it wanes on it.

Sorry. Had to get that one out of my system.

-:G:-
Gryf Ketcherside

This thread was discussed between 22/04/2009 and 01/05/2009

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