Starter motor plastic cover removal

[Charles Farran]

Dave,
The starter relay sends power to the solenoid which in turn moves to make the starter motor crank the engine via the WR wire. At the same time this should result in the terminal on the back of the solenoid to which the W/LG is connected being made live to feed the coil at 12 V. (Certainly higher than the ballasted route once the engine is running). As the starter cranks , it indicates the starter relay is working. If the W/LG terminal is live under cranking ,then there is probably a break in the W/LG connection to the coil. You could make a temporary connection from this terminal to the coil , leaving the existing connections in place. If the engine starts as you crank & continues to run after you have released the key then you will have identified the problem. If the W/LG fails to go live as the starter cranks , then it suggests something faulty within the solenoid / starter assembly itself.
Cheers,
Charles

[Dave Wheatley]

Good idea Charles. At the moment I have got other jobs in hand on the car which preclude starting her up. Probably next week will try it.
While I am on it, Why can't the 12v feed to the coil when starting be taken direct from the main red/white solenoid terminal?
On my solenoid, the main brown wires are on the thick terminal with the nut. Next up red/white and top green/white. Does this sound correct. It could be possible to reverse the red/white and green/white terminals.

[Charles Farran]

Dave,

I suspect it has to be on a different terminal to ensure it goes "dead" once the engine has started & cranking finished , otherwise you would get current passing back from the piggy back connection on the LT side of the coil where it meets the ballasted lead when the ignition is on & the engine running - this in turn would try to stir the solenoid into life....
If i recall rightly (as i have misplaced my hand written diagram of how the wires were wired up to the back of the solenoid & don't want to have to pull the boot off again for some time............................) the wiring was in the order you indicated. I'm sure some one else will be able to confirm the order.
Cheers
Charles

[Charles Farran]

Dave,

Thinking about it a bit more , the WR feed & terminal gives power to the coil of the solenoid & the W/LG terminal must be connected in parallel to the starter motor internal wiring that is made live when the solenoid bar is moved by the solenoid coil during cranking. (This applies to 1974 1/2 - 1980 cars) as this additional terminal wasn't there on earlier cars.

Cheers,
Charles

[Dave Wheatley]

Charles.
Call me a cynic, but I suspect the green/white and red/white terminals on the solenoid are directly connected inside the solenoid. Fingers crossed the starter relay doesn't pack in, allowing what you mention to happen.
If I'm right, when the car is running there will be a feedback of 6? volts from the coil to the solenoid, which should be too low a voltage to energise the solenoid, and onto terminal C2 on the starter relay which should be not connected to anything during normal running.
Conspiracy theory?

I'd penned this post as you were doing your last post Charles, so I'd not read it.

[Charles Farran]

Dave,
They are not directly connected. The R/W terminal energises the solenoid coil that moves the bar within that coil that then moves to create a link internally between the large terminal that has the big power cable from the battery to the starter motor internally & i think the W/LG terminal is linked to this starter motor wiring & hence only becomes live at the same time as the starter motor itself - hope that's clear!
Hence it wouldn't work if you connected up the wiring the wrong way round & you might be in danger of trying to turn the starter motor with the RW wiring rather than the heavy duty main feed from the battery , depending on how the internals of the starter motor are put together.
As your starter cranks , that suggests that at least your RW is correctly connected.
Cheers,
Charles

[Dave Wheatley]

Just letting my mind wander in these covid ridden days Charles!

[Michael Barclay]

Hi Dave
Charles description of the wiring /solenoid operation is correct. The white/LG wire has to be on a separate terminal otherwise with the ignition on, the solenoid would be constantly powered from the coil /ballast resistor circuit. Although this may not be enough voltage (6 – 9 volts) to engage the solenoid, it would risk eventually burning out either the solenoid or ballast resistor.
By far the easiest way to check if things are working correctly (and avoid a lot of groveling under the car is to measure the voltage on the + coil terminal. (The 2 x white/LG wires. one goes to the ballast resistor, the other to the solenoid.) This will also help eliminate the ballast resistor and relay. With the ignition on measure the voltage between the + coil and ground. It should be between 6 – 9 volts. If not suspect the ballast resistor. However you say the car starts when you release the key so this suggests this is all OK. Next measure the voltage with the key turned to the cranking position. The voltage should rise to full battery voltage. If it doesn’t, then the problem is either a break in the White/LG between the coil and solenoid or the solenoid itself. A simple continuity check with a mulitmeter will determine a fault in the wiring. If this is OK then I would pull off the white/LG from the solenoid and connect your meter (Set to DC volts.) to the solenoid terminal. Get an assistant to turn the key to the crank position why you measure the voltage on the terminal. It should give full Battery voltage when the key is turned and no volts when released. If not then I suggest the problem is the in the solenoid requiring removal and a strip down.
Hope this is of help
Mike Barclay

[Dave Wheatley]

Thanks Michael. Point taken about the possibility of damage to the solenoid. My assertion that the 2 terminals on the solenoid were permanently joined was not really meant to be taken seriouslly. Anyway, just back from my now non starting MGB. There's a spark at the plugs when cranking, so hopefully my wiring is OK. Could be dud fuel - it's 3 months since I had the car running. Bck to the car with a spare cbattery shortly.

[Michael Barclay]

Hi Dave
Good news .Sorry if my reply was a bit OTT but there has been so much comment on this forum about problems with the car ignition systems on rubber bumper cars, especially around the 12 volt feed terminal (*)to the coil on the solenoid. (*or lack of a terminal on some of the new starter motors being sold now)
Sounds like you are well on the way to getting the car running again, maybe the fuel pump just needs a whack to get it back to life. Let us know how you get on.
Mike Barclay