MGB Register Forum

Hi Vic,
I agree with you - the solenoid attached to the later starter motors is very much like a relay.i understand that the solenoid & the relays used up to the end of the MGB production run had lower resistance coils than relays made today.They required more current to drive them & therefore provided more of a barrier to a supply voltage (or do i mean current) in the wrong direction where with more modern relays a diode may be required as extra protection.(A couple of years ago i bought 4 + modern square relays with the intention of replacing the round ignition & starter relays & adding ones fro the headlight circuits & fuel pump. At the time the specialist supplier recommended relays with internal diodes for i think both the ignition & the starter relays to ensure no running on etc. In the end i stayed with the original set up as i may go down the LED headlight route where the loading on the headlight switch will not be so great. (So far i have changed all the internal lighting & the rear number plate lights to LED). - Sorry i am going off topic again.... I did however put an in line fuse for the overdrive supply which is an absolute essential for all MGBs/MGCs & MGBV8s as the feed is always live when the ignition is on & any short will create a fire!
Cheers
Charles

Charles, the same type of starter motor, Lucas 2M100 was fitted to all GHD/N5 B's from 258001.Only the wiring diagrams for rubber bumper cars with ballast ignition show the. "cold start" terminal on the solenoid. Was a different solenoid fitted for ballast resistor ignition?

Hi Vic,
It was at the time the RB cars came in in mid 1974 that the ignition system included a ballasted ignition coil & the starter solenoid on the back of the alternator was modified to include the terminal marked IGN (the third one in one of my earlier posts). Again , with credit to Rick Astley he says "Cars from 1967 onward can all use the post 1974 starter motor assembly.However,if a RB car is fitted with an older solenoid, it will not have an IGN contact." He then gives circuit examples for using either relays or diodes for retro fitting a ballasted system on pre RB cars that could also be used for connecting up a ballasted system on a RB car where a later replacement starter motor with the IGN terminal is not available. (Hope that's clear)!
I can't recommend his book hard enough!
Cheers
Charles

Strangely enough Charles I've just this second read that particular passage. There must be something in the later starter solenoid that prevents feedback from the coil. So, if anyone with a rubber bumper B wants a replacement starter make sure it does have the cold start connector.
I was wrong. You can't piggy back an existing terminal, it must be the correct one for the cold start circuit. The same would happen if the wire was connected to the starter relay as Mike suggested and I thought would work. I wrongly thought the relays would prevent any feedback but a diode must be used on earlier cars, or if the starter solenoid doesn't have the cold start connector. So it has to be the correct starter motor. Grovel, grovel. Thanks Charles.

A very interesting thread.

I've had my 1978 gt for 2 years now. It has always had an unusual way to start. It will only start when the ignition key is returned to the run position. When I first got the car, it would churn over for ages not firing. I gradually realised that it only fired when the key was released, and now that I know, it always starts after a 2 second blast and release sequence. It has never failed even in winter. Maybe this is connected with the 12v feed to the coil from the starter solenoid (if there is one - not sure if I've got an original starter, and it's difficult seeing the solenoid wiring). I'll try and do some voltage readings on the coil today on starting and running operations.

It does sound like there is no direct 12v supply from the starter solenoid to the coil. Maybe the starter isn't original and has no facility for the direct feed to the coil.

Do you ever wish that you hadn't started something?

At the ignition on position, there is 6.3 volts at the coil which seems OK. On oerating the starter, the voltage is all over the place 2 to 13 volts. Engine running shows 11 volts at the coil and 13.6 volts on the car voltmeter. The car has been running like this for around 5,000 miles with no ill effects.

It will be interesting to here what the source of Dave's problem is. You cannot see the back of the solenoid on the starter motor if the rubber / plastic cover is in place and over the years i have only removed mine a couple of times as it is a pig to ease off & get back on again. (I last removed mine over 2 years ago when i refurbished everything under the bonnet. (I found that leaving the cover in the sun or warming it up with a heater made it much more supple). When replacing it i was concerned about dislodging the feeds to the tag terminals (number 2 & 3 as per one of my earlier posts).
If Dave's starter motor is the later type with the IGN terminal, then you could check without the ignition on , with a continuity meter,whether the lead at that end at least would complete a circuit to where the lead attaches to the coil. (Simply detach the lead at each end). You would then know it is not the wiring per se.
You could then attach a meter lead to the IGN terminal, removing the leads to the coil +, & then attach the other meter lead to ground. Then crank the starter and measure the Voltage & see if you get a voltage significantly higher than 6. (I doubt if you would get 12V due to the starter load - you would probably have to disconnect the main lead from the battery from the back of the solenoid , but make sure all the browns are joined to the main battery away from the starter motor but isolated from the body otherwise dangerous & therefore probably not necessary as you will have proved that the IGN contact on the back of the solenoid works)!
Cheers
Charles

Hi ,
I sent my last post not being aware of Dave's post at 12.15.
I am surprised you are getting 11 Volts at the coil when the car is running. Is your coil a ballasted one i.e. a 6V or has it been replaced with a non ballasted coil i.e. a 12V? If you are getting close to 12V when running then if it is a 6V coil it will run very hot & break down. Has a PO replaced the original 6V with a 12V? Has the original wiring been played around with?
Cheers
Charles

Hi Charles ta for the input.

The coil doesn't have any id. Any meter tests to determine voltage?

The car has done a few 000 miles in this state with no problems including a few several hour continuous runs.

It was only this thread that got me checking!

Wiring appears to be unmolested, but I can't get at the starter solenoid - old age and accessibility - to check.

One thing that puzzles me is how does the 6volt supply get cut off when cranking in the normal ballasted system, or doesn't it?

When I got the car it had had a new ignition switch fitted.

The car has always been a good starter, subject to my remarks in my first post, so I am minded to fit a known 12v coil and see what happens.

Edit. Meter readings indicate a 6v coil. The solenoid on my car is underneath the starter! Cancelled fitting 12v coil.