Starter Motors for MGB's with Ballast Resistor Ignition.

[Vic Butler]

Evening Charles.
Dave had said that his MG has always had the problem in his ownership so I wonder if a previous owner has replaced the starter and either it's wired incorrectly or doesn't have a cold start connector.
The only way would be to examine the starter motor solenoid connections, not an easy task.
I seem to have opened an interesting can of worms here. I have been tempted to replace the bulky Lucas starter motor with a modern high torque type as the one on my Land Rover is excellent but as the MG's starter is working fine I'll abide by the old wise saying, "If it ain't broke, don't fix it."
This is what I wrote when I replaced the ignition relay.
Ignition Relay:- (front one)
Terminal 87 white/brown wire.
Terminal 85 black wire.
Terminal 30 2 brown wires.
Terminal 86 2 white wires.
Starter Relay:- (rear one)
Terminal 87 white/red thick wire.
Terminal 85 black wire.
Terminal 30 brown wire
Terminal 86 2 white/red wires.
Hope this helps. All the relevant relays have the same terminal numbers
This would have been helpful earlier but I've only just remembered I wrote it in the front of the repair operation manual.
Dave, the ballast resistor feed to the coil is bypassed during cranking. The ballast resistor circuit is energized via the fuse box by the white/ brown wire from the ignition relay and as that is cut off during cranking then only the 12v supply from the starter solenoid is activated.

[Dave Wheatley]

Thanks for the relay wiring guide Vic.

I must admit, I love these esoteric mystery problems, and love solving them even more!

[Charles Farran]

Dave,

If your Lad is able to social distance from you (& in England he can't be in a different household's garage) & get under the car he could view the back of the starter motor to view the solenoid & determine if there are 3 points of contact which would establish if it is the correct starter motor / solenoid for a ballasted system. I needed to jack the front of the car quite high with a trolley jack (+ axle stands) & remove the offside front wheel to get sufficient access. He could then pull the weather cover forward (assuming one is still covering the starter motor as they are often missing) & down to expose the wiring connections. He could then check the continuity of the green & white wire (with the ends disconnected at the solenoid & the coil end as suggested in one of my earlier posts to at least eliminate that issue.He could also check that the IGN terminal on the back of the solenoid (if there is one) is not live when the car ignition is on,but not in the cranking position). If it is live when the ignition is on , but not cranking, then that may be the source of your 11-12 volts at the coil when the engine is running. If that is the case, then that will need following up! I am not sure if the starter motor would work if the 2 separate leads with female spade connectors were connected the wrong way round & whether that might have created your problem but worth checking that they are.

Cheers

Charles

[Vic Butler]

Dave, when your lad can check the connections on the starter solenoid, the white/light green wire must be on a stand alone connector. If it's sharing with another wire, there's your problem. If it is sharing, is there a spare connector? If not, the solenoid is the incorrect type for ballast resistor ignition.
Try to identify the make and type of starter motor fitted if possible.
The coil on my MGB GT is a Lumenition ballast resistor type to match the Lumenition Optronic Ignition.

[Dave Wheatley]

Did some checking with the self proclaimed expert.

Both relays had the earth and trigger connections reversed, but putting them right hasn't made any difference. All the connections checked and appear to go to/come from the correct points.

Still shows 10.5 volts in the run position.

So, I think the answer lies in the solenoid, which as I've said I can't do anything about at the moment. Took the car for a 50 mile shopping trip, and running fine.

It would be nice if somebody could check their running voltage for comparison.

[Charles Farran]

Hi Dave,

Glad to hear at least that the car runs!

I have spent a little bit of time looking at some archive material on another site.

There was an instance where one individual couldn't start his ballast system car. When the white / light green wire was removed from the back of the solenoid, the car started. Unbelievably it was diagnosed as a short within the solenoid which might be occurring when you crank your car & it doesn't fire until as i understand until you release the ignition key & then the engine fires up. (Until we know what type of starter / solenoid you have this possibility can't be established). It would be interesting to know, if the white /light green wire was removed at the coil end leaving the ballast feed in place, if you started the car as i think you have been doing & then measured the voltage at the coil if it was then closer to 6V.

I understand also that 1978 was a change for the ignition wiring. In 1977 power for the coil & ignition powered electrics came from the ignition relay. In 1978 the power for the coil was moved to the ignition switch. A 1977 car has one in line fuse from W/N to G & a 1978 car two.
Is your car a 1978 model year or a late registered 1977?

I think you said the ignition switch had been replaced - they can create some weird issues

Cheers

Charles

[Dave Wheatley]

Hi Charles, thanks for your interest in this saga.

The car was registered August 1978. There are 2 inline fuses in the vicinity of the 2 relays if that helps.

On my car, the 2 green and white wires are joined in a single connector at the coil which I don't want to disturb if possible, but yes, to cut off the white/green coil to the solenoid would hopefully reveal if there was a fault in the solenoid. The fluctuating voltage to the coil when cranking is weird.

[Vic Butler]

Charles, my October 19th 1977 built BGT has the two fuses below the relays.
The Land Rover will be going shortly for a new bulkhead to be fitted so I can then drag the MG out of the garage. I'll check the voltage on the plus terminal of the coil with the engine running.

[Charles Farran]

Hi Dave,
I think you will get some fluctuation in the voltage when cranking given the load of the starter motor.
As the 2 leads are connected at the coil end that suggests original wiring at thst end so that test will have to wait until you can get to the other end!
Sounds like you have the.1978 model year then.

Cheers , Charles

[Charles Farran]

Dave
One other thing might be worth checking.
The original relays as fitted were identical. Have you tried swapping the relays round to see if you get the same results?
I think you said one was a newer replacement. If the results are the same then you will have eliminated the relays as contributing to the problem.
If not, then you may have part of the answer.
Cheers,
Charles