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MG MGB Technical - Starter Wiring

Hello everyone,

My 70B wouldn't start today. The starter does not engage, but I hear a load click when I turn the key. Is this the solenoid? I hunted around under the car and found that a small brown wire has disconnected from the starter. I'm assuming this wire connects with one of the two bolts on the starter. Can anyone tell me if this is the case, and if so, which bolt the wire should be connected to?

Thanks in advance!

Greg
gks greg

Brown wires are permanent live (+12V), Likely there is a small terminal that it has come from where more brown wires go. At a guess, the other end goes to the alternator- maybe you haven't been charging, and the battery is flat?


The starter should have a thin wire connected to a terminal by itself, there are 2 possible colours for this thin wire:-

If the wire is white/brown striped, then it is the wire from the starter relay, and goes to the small terminal by itself on the starter motor.

Or a red/white striped wire connected to a terminal on the starter if there is no relay, it connects to the relay if there is one (and the relay supplies current to the brown/white wire instead) - confusing eh?

The solenoid should be part of the starter motor, a cylinder on the side with 2 large nuts, one caries all the brown wires, and the thick wire that goes back to the battery, the other carries one thick wire that goes directly inside the starter.
Switch the headlights on, if you can feel the solenoid clonk when you activate the starter, and the headlights don't go out, then there is a fault with the starter motor itself, the connection to the motor, or the contacts inside the solenoid.
If the lights go out, you either have a flat battery, or the starter is seized (or the engine).

Martin Layton

If it is loud then it probably is the solenoid, which is low down on the right-hand side of the engine. But first make sure it isn't the relay which is high up on the inner wing by the fusebox. If it is a white/brown (it would only be white/red on earlier cars without the starter relay) then it should be the relay you are hearing. This white/brown goes to a spade on the solenoid.

There could be several brown wires on the solenoid stud with the main battery cable (later cars) or on individual spades (earlier cars). None of these would directly cause the problem you mention, although it could cause the battery to not be charging and so eventually run down past the point at which it will crank. However this usually causes a chattering solenoid rather than a single click. It would also cause the ignition warning light to glow dimly. If it is battery charge then any lights that are on when you try to crank will dim right down.
Paul Hunt 2

Hello Martin and Paul,

Thanks very much for your comments. I've reattached the wire to the lower bolt on the solenoid. The wire is definitely brown.

Unfortunately, this hasn't solved my starter problem--I still just get a load click when I turn the key. I checked the battery and the current to the solenoid and both appear to be fine. Do you have any thoughts on the possible cause of my troubles?

Thanks again,
Greg
gks greg

If the electrical connections are clean and secure, try tapping the starter with a hammer. Worn bushings can cause a starter to lock up.
Kimberly

Greg,

Take the usual precautions, and get underneath. (Make sure that you are in neutral)

Try removing the thin striped wire at the starter, and joining the terminal it came from to the terminal with the brown wires on. The starter should engage and turn the engine over. If it does, your problem is with the wiring from the switch to the starter relay to the starter motor.

If it doesn't work

With a screwdriver, carefully bridge the 2 large terminals on the starter.

If there is an almighty spark, but nothing happens, the starter is jammed.
If absolutely nothing happens the starter motor is faulty.
If there is a spark, but the motor runs, then the solenoid on the motor is faulty, or it is not switching.

(The engine won't turn over during these tests, don't connect for long, expect a spark, and damage to the screwwdriver)

Martin Layton

You could try putting the battery on a charger. My lights and everything else worked, but there wasn't enough to turn the starter. A gentle tap with my favorite precision tool...a 3# hammer...also will help clear the solenoid on occasion...Ken
K Bonn

Check the voltage between the solenoid stud and the starter body while you are cranking. If it shows 12v the solenoid (assuming it is the solenoid that is clicking and not the relay) isn't connecting power to the starter motor, so it will have to come off and be investigated or replaced.

If the voltage shows lower than 9v either the battery is weak or there are bad connections beyween battery and starter. Do the same test on the battery *posts* (not connectors) and if you get a similar low voltage it is the battery. If that shows 12v or nearly so it is connections. Test again between the 12v post and the body, the 12v connector and the ground post, the 12v post vand the starter body, and the ground post and the battery lug on the solenoid and you shoudl be able to work out where the bad connection (could be more than one) is.

With the starter could be burnt contact surfaces on the solenoid, worn bushes or dirty comm on the motor, or possibly damaged wiring on the motor rotor.
Paul Hunt 2

Hello everyone,

It appears that my problem is the solenoid. Martin--when I short the solenoid by placing a screwdriver across the two bolts the starter fires up just fine. The starter/solenoid is original to the car, but the car only has 30k miles (I just got it a couple months ago). Is my best solution to replace the whole starter/ solenoid, or should I just fix the solenoid? In other words, does a bad solenoid indicate the the starter will go bad soon too?

Thanks again,

Greg
gks greg

Did you try connecting the small terminal on the starter to a live?
If it went "clonk" nicely, but the starter didn't move, then the fault is in the solenoid.
If it turns the engine over, the fault is in the ignition wiring.

Assuming that you tried the other tests, one thing you can do is take off the starter motor: disconnect the EARTH lead off the battery first.

The solenoid is held on by two bolts. (Once you undo the thick wire leading into the starter)

I'm working from memory here, but I think that the end cap with the terminals on will come off when those bolts are undone. You can then see a thick piece of copper alloy on a spring, which is what bridges the two terminals when the solenoid pulls backwards. Usually, this just requires cleaning, along with the contact area of the terminals.
I think I have turned the copper plate over before now to reveal a clean surface.

On re-assembly, the motor should work for quite some time if that is the fault.

I suppose it is worth checking the motor brushes while you have the motor off, but as I don't have any spares I wouldn't bother personally- if it ain't broke don't fix it! is now my motto.

Don't mess with the fork pivot screw- with a nut on it. It adjusts how far out the pinion goes. (See my motto for guidance)
Martin Layton

Replacement starters with lifetime warranties are available at Shuck's for less than $100-. Take a print of the starter from their website to the store if choose not to mail order to get the best price.
Kimberly

Depends what is wrong with the solenoid. If it is a silly fault on an otherwise good starter then it is worth effecting a repair. But if it is a well worn starter and the solenoid contacts are well burnt, and the brushes well worn, a complete replacement will probably save more work on the old one in a relatively short time. I say 'probably' as Hunt's Fifth Law states "Many break-downs occur soon after a car has been worked on; 'new' parts can be faulty when you receive them; 'new' parts will sometimes fail soon after fitting; 'new' parts almost certainly won't last as long as the originals."
Paul Hunt 2

Hello again,

I like to say thanks to all who offered advice. I pulled the started off and cleaned up the copper plug inside the solenoid--this seems to have fixed my starter issues.

You will probably be hearing from me again soon, as I've now launched into the rest of the car's problems...

When I started this thread with "My 70B wouldn't start today...", I could have more accurately stated that: "My 70B hasn't started in 8 years because it was sitting forgotten in someones barn until I picked it up last month."

My first project was to get the odor of dead mice out of the car so that my wife yelling at me about the awful smell emanating from our garage. Needless to say, I'm sure I have quite a bit more to do before its out on the road again.

Thanks again for you help,

Greg
GKS Scott

This thread was discussed between 02/08/2007 and 14/08/2007

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