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MG MGB Technical - Ignition warning light.... ground strap?

I have been having an issue on and off recently with the ignition warning light coming on after I have driven my 74B for a couple of miles. After that it sometimes comes on and off, but today for the last mile to work I noticed that the light instead of being completely off or bright red it was a faint red colour. I parked the car and decided to check the connections and also the belt tension. The tension seemed ok, but on further inspection I noticed what appeared to be ground strap dangling between the hose to the radiator and the alternator itself.

If you take a look at the photo link below you will see one ground strap which goes to the engine and the other which I am not sure if it is supposed to be connected, and if so to what... I know is a silly question, but could this be the cause of my ignition warning light?... Lets hope I can drive the three miles back home from work!

http://members.cox.net/gerryg28/ground.jpg

Thanks

Gerry
GG Ginty

Theyre not ground straps... Where do they go from and to?

N
Neil

Neil

They end is not connected to anything as you can see. The cable itself is part of the group of cables connect directly to the alternator.

GG Ginty

Gerry. As Neil notes, these are not ground straps (which are large, braided connections between the engine/transmission and the chassis), nor does it seem to be a ground wire (which would be black in color). Therefore, there is a good chance that this wire is live (hot/carrying electrical current) when the engine is running and may be shorting out as it flops around/is blown around while you are driving.

What is the color of the wire? Normally, they are some basic color and often they will have a stripe of a different color. By knowing the color, and the fact that the wire is near the front of the engine compartment, you can take a wiring diagram and determine what it may have been hooked up to.

I do not see this as being part of your alternator problem unless it is grounding out, perhaps not even then. Paul Hunt or David DuBois might be able to tell you if an intermittent short would cause the ignition warning light to act as you describe.

But, not a good thing to have flopping around as you are driving along, particularly if it is live. I think I would wrap some tape, preferably electrical tape, around it before the drive home.

Les
Les Bengtson

The thick braided strap is normally round the left-hand (facing forwards) engine mount on chrome bumper cars, and round the gearbox mounts on rubber bumper cars.

Side marker lights were fed from blue wires until the 73 model year, i.e. only on with headlights, red from 73 on i.e. on with both parking and headlights. If those wires are blue as they seem to be then unless you have the wrong year they are not factory wires and so could be for anything. Could be a tracer colour which I can't see, in which case blue/white is main beam and blue/red dipped, but again if not those then they are not factory.

The ignition warning light will come on if there is a significant difference in voltage between the brown/yellow at the alternator and the white coming off the ignition switch. The most common cause of this is alternator output failure, but it can also be caused by bad connections in the brown from the alternator down to the solenoid, and from there up to to the ignition switch, and through that onto the white where it goes to the warning light, fusebox, coil etc. Partial shorts can also cause the same thing by trying to draw much higher current than usual through 'normal' connections, which will cause a higher volt-drop than normal, which again gives the voltage difference to light the lamp. But I'd expect this to do some heat damage to the wiring, with smoke and the associated smell

If taping up the wires doesn't solve the problem then you need to measure the voltage on the brown and brown yellow at the alternator, and the brown and white at the fusebox when the light is glowing and the engine is running at a fast idle. You should see about 14.5v at all of them, 2 or 3 tenths of a volt difference between any of them is acceptable. But if you only see 12v on all of them the alternator isn't charging, larger differences between brown and brown/yellow at the alt are also probably a faulty alternator, and correct voltages at the alternator but significantly lower at the fusebox are bad connections. These, as well as some alternator faults, will cause the warning light to glow brighter as more electrical things are switched on.
Paul Hunt

This thread was discussed between 20/05/2009 and 21/05/2009

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