MGB GT Episode 55 Alternator

[@carstenmoore5760]

Hi Henry, I was about to comment on your video but see others have beaten me to it. Your ignition warning light is actual connected in a roundabout route to the same multi point connector which serves the fuel pump and overdrive. You are also correct that as your vehicle has a ballasted ignition system, 6 volts on the white wire with green tracer at the starter solenoid is exactly what should be recorded. The cable you tested is the one that would supply a temporary 12 volt connection when the engine is being cranked over by the starter. The increased voltage provides a bigger spark to aid starting. The ballasted system came about as early MG's and other cars of the era would be difficult to start if the battery was slightly down in performance or in cold weather as most of the power from the battery would be taken by the starter motor meaning the ignition coil would struggle to provide a decent spark (known as coil robbing). In simple terms your engine ignition is a 6v system, boosted to 12v when the engine is being cranked over. Another piece of useless info for you 😉.

[@HenrysGarage]

Thanks Carsten, really good info to help me learn. Thanks

[@garethgoodchild2643]

Good sleuthing Henry. Seems to be sorted however, I didn’t see the light come on when you turned the key. Usually the light comes on then goes out once the engine starts.

[@HenrysGarage]

Blast - you're right. It's not coming on at all now. Back to the drawing board

[@HenrysGarage]

But I've just sorted it now - loose cable

[@garethgoodchild2643]

That’s good. It’s usually something minor especially when you have been taking things apart. Which wire was it? Is the car running a bit smoother now?

[@HenrysGarage]

@@garethgoodchild2643 I hadn't clipped in the alternator wires correctly. I think I was running on battery only! The roughness was also because I had a problem with the fuel pump again so I replaced some wires corrected with tape to using bullet connectors but failed to re-tighten the earth. It was rough because the pump was coming on an off. Really embarrassing

[@David-wy9jl]

On my 74, when you turn the key on the red charging light always comes on. When the engine starts, the light then goes out. It looked like when you turned the key and heard the fuel pump clicking, the light was off. Maybe it's different for your year?

[@HenrysGarage]

No David, you are right. It used to and should be coming on. I hadn't noticed. Back to trouble shooting

[@HenrysGarage]

But I have sorted it now - loose cable

[@george5022]

Have you sorted the overdrive problem ?

[@HenrysGarage]

I haven't done yet. I'm coming to the conclusion it is going to require a rebuild. Before I do that I want to do another test on the solenoid and check it is working properly. If not, I'll replace that but then I am left (I think) with taking the transmission out, which means also taking the engine out, and I do not have the tools (crane or engine stand) to do that currently so I will probably live with overdrive not working for the time being. Since I will probably avoid motorways without overdrive it means I'll have to stick to the fun A and B roads in the short term. What a drag

[@blackvanandrobin6413]

Cheat you didnt re connect the red light. Report to my office for detention !!!!

[@HenrysGarage]

I do like a short cut, but I missed this one

[@HenrysGarage]

You were right - I had cheated without realising it. But I've now plugged it in and it comes on with ignition but goes off with engine!