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MG MGB Technical - Starter Wires ???

I am changing the starter on my 1980 MGB. However, the strater I purchsed only has one slip connector, and the rest of the wires connect to the main lug. However, my old original starter has 2 small slip connector wires. What is the difference? Can I splice the 2 small wires together, and then just plug them onto the one plug? One of them on the original starter is marked, "ignition". The secomd one has no marking. This new starter also is marked "ignition" but as I stated, it doesn't have the second connection.

Please help,
Danny 1980 MGB LHD
Danny T.

The smaller spade terminal on the original starter supplies 12V direct to the coil for starting and bypasses the resistor wire that normally drops the voltage to the coil.

If you still have the low voltage coil fitted then you will need to connect the smaller wire to a 12V source which is only activated when cranking - I would not recommend using the other spade connection which comes from the ignition switch because you will overload the switch - use the heavy post that goes to the motor.

If your car has had the resistor wire bypassed and a 12V coil fitted then you can ignore the smaller wire.

In both cases you must connect the red/white wire to the larger spade terminal or you won't be able to start the car!
Chris at Octarine Services

Thanks Chris,

That all makes sense. However, you mentioned connectiong the smaller spade connector to the main lug. Isn't that main big lug "hot" at all times, even when the ignition switch is in the off position? I know that all the other bigger wires are connected together on the main lug, and one of them connevcts to the headlights, which will work with the switch off. By doing this, woukld it not drain the battery?

Thanks for your response,
Danny
Danny T.

To get the 12v boost for the 6v coil you will need an additional relay that operates at the same time as the starter relay, or change the starter relay to one with two normally open contacts instead of just one.

Connecting the wire that should go to the small spade (white/light-green) to the big lug with the starter wire (white/red) will cause the coil to overheat during running, but more importantly will effectively keep the ignition on all the time preventing you from switching off the engine, flattening the battery even if you stalled it as you say.

I've never done it but connecting the two wires to the big spade at the solenoid, whilst it may not overload the relay (not switch), would feed coil voltage back to the solenoid during running. This may cause the solenoid to remain operated hence continually spinning the starter when you release the key, but even if it doesn't do that it would significantly reduce the voltage to the coil even below the normal 6v during normal running.
Paul Hunt

Danny : sorry to state the obvious, but ,take the starter back to the rebuilder/parts store and get the right one. You can make the one you have work ,but why bother? If it worked before your starter failed, the right starter is the way to go RIC
R E L Lloyd

Danny & Paul,

NO - not the main feed post that is connected to the battery lead but the other post that is connected to the starter motor itself - this is only live when the starter is working.

This replicates the action of the small second terminal on the old starter which is made live by the action of the solenoid which has a small secondary contact attached to the main contact in the solenoid.
Chris at Octarine Services

Thanks Chris,.. Connecting to the big lug on the "starter itself" DOES make sense. I appreciate the tip. I think I'm going to try that.

To answer the question REL Lloyd asked, I can not use the correct starter. You may have read in my other postings, I am undergoing a Rivergate 5 speed conversion. With the rivergate kit, the original starter, (1972 thru 1980) has a longer dog drive gear, which hits the new flywheel. The older style, (1968 thru 1971) starter has the shorter drive gear, which fits and works perfectly. Therefore, I am converting over to the earlier type starter. With the original factory flywheel and transmission, ALL MGB starters 1968 thru 1980 will interchnage and work. Only a problem with the transmission conversion.

Thanks for all the input. I'll let you guys know the outcome of the wiring and the trans. conversion as soon as I'm finished.

Danny
Danny T.

Chris - I suggest that makes the coil voltage situation even worse, since the starter motor will present an almost full short between the coil +ve terminal and ground. Thus nearly all the 12v will be dropped across the loom ballast leaving virtually none for the coil. Again, I've not tried this, I'm just using Ohm's Law.

As far as I was aware the small second terminal is disconnected from *everything* when the solenoid is released, not connected to the motor.
Paul Hunt

Paul,

Yes I think you are right there - I hadn't considered the starter motor load on the supply from the coil once the key was released!

So the only option is to use a relay to mimic the solenoid contact.

Or change the coil for a 12V one and bypass the resistor wire.
Chris at Octarine Services

You can just leave the resistor bypass wire disconnected. Will only give you grief in really cold situations.

This would be my first choice as there is no real problem usually. If it gives you trouble from dead cold, you can add a little 2 dollar 'ice cube'relay to do the same thing, just provides straight 12v to the coil only during cranking.

All my current g/r starters for the b have the second terminal, but since other people's don't there are available diodes to to the same.

keith
Keith Gustafson

If you use a diode instead of a relay it needs to be about 10 amps.
Paul Hunt

This thread was discussed between 11/12/2003 and 13/12/2003

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