Dear All,
My Mk2‘s ignition warning lamp is permanently on when the ignition is on independent of engine revs. The correct filament bulb is fitted.

The wiring at the voltage control box (RB 310) does not agree with the original wiring diagram: no wires are connected to pole D; there is an unconnected 2-wire cable (2 wires connected together) which I assume has been disconnected by a previous owner. By connecting +12V from the battery to these wires, the ignition light goes out. This suggests that one of the 2 wires is routed correctly to the ignition warning lamp and the other is earthed.

The car is negative earth and, I believe, fitted with an alternator. The ammeter works.

Has anyone experience of a conversion from dynamo to alternator and how the control box is wired to maintain the correct function of the ignition warning lamp?

Thanks in advance,

 

I wrote a thread for the S Type forum about converting from positive to negative earth which showed which wires on the RB340 regulator went where. Here is an extract from the thread. The full thread can be read here.
https://www.jagstyperegister.com/for...ive+earth#p802


There are two wires coming from the Dynamo one large one small. The large one goes to the “F” terminal on the regulator control box and the small wire goes to the “D” terminal.

On the regulator control box from top to bottom the terminals are marked as “E” which is an earth and this wire is attached to the inner wing by a screw.

Next is “D” and this is where the small wire from the Dynamo is attached.
Next is “W/LT” which I assume is for Warning Light as this wire runs back in to the car and to the Ignition warning light.
Next is “F” and has the large wire from the Dynamo attached.
Lastly there are two terminals marked as “B”. The lower wire is a live wire for your inspection socket. A small round socket on the inner wing which you can attach an inspection lamp to. The other wire is your live which charges your battery and runs the electrical systems for the whole car.
Now I would have given you colours for these wires but most of mine are so faded and dirty that you cannot see what they are supposed to be hence the continuity tests.

Of the six wires mentioned you actually only require two of them and they are terminal “W/LT” and the main wire for charging the battery on terminal “B”. This wire does not actually go straight to the battery or the solenoid or even the ignition switch but goes to the Amp meter just to confuse things. On the back of the Amp Meter there are four wires, one incoming from the Regulator control box terminal “B” which is the central of the three large connectors you see when you look at the back of the Amp meter. The two either side power the ignition switch on the right and on the left is the power to the main fuse board. There is a forth wire connected to the left terminal at the back (difficult to see) which powers the lights circuit. We are only interested in the main wire from terminal “B” in the centre connector and the left hand large connector as these have to be swapped around when converting to negativeearth to make the Amp meter read correctly.

 

Thanks for your input Cass. My case is different because of the alternator instead of dynamo.
The following article discusses the subjectGenerator to Alternator conversion

In the meantime, I’ve identified the wire to to ignition warning lamp but still have to decide where to connect at the alternator…

 

Just an afterthought. Considering that conversion from dynamo to alternator is so popular, I would have expected to find a wiring diagram for the alternator case.

Can anyone help with this diagram?

 

Dave if you read the whole thread it is about converting from the generator to a dynamo. The dynamo used is called a "Dynalite" which is companies name for it and is the type that looks like the original generator but has the internal workings changed to a dynamo and allows the PAS pump to still be fitted to the back. The thread I wrote goes on to say,

"So having established where the wires go, from the Dynalite instructions we require a small wire to the ignition warning light and a large wire going to the ignition circuit. For this you can ditch everything attached to the Regulator control box apart from the wires connected to terminals “W/LT” and the wire from terminal “B” to the ignition. I connected “W/LT” direct to the small terminal on the Dynalite and the wire from terminal “B” to the large terminal on the Dynalite having shortened the cables and put new terminal connectors on the wires."

So to explain there should be two wires connected on the alternator, Large terminal and small terminal. The large terminal is the wire that used to go to "B" on the RB340 which ends up on the S Type at a terminal on the back of the Ammeter in the dash then runs to the solenoid on the bulkhead and charges the battery. The smaller terminal on the alternator is "W/LT" on the old RB340 which runs all the way up to the ignition warning light on the dash.

 

Does this car have Power steering? Cass has given you everything you need.

 

Cass: thanks that part of your discussion is similar to my case. I find the drawings in the MG article very helpful: a picture is worth more than a thousand words!

Glyn: my Mk2 originally had hydraulic power steering. A previous owner added electrical power steering in addition. I removed the hydraulic power steering in the sense of the pump and reservoir and reconditioned the original steering box, connecting the input to output together - as explained in another thread.

 

See post 3 here for small terminal.

https://www.jaguarforums.com/forum/m...s-type-238865/

 

Small & Large terminals are obvious.

 

One other thing, if the ammeter is still in circuit be careful that its suifficently rated for the output of the alternator, the power of the dynamo was a lot less than modern alternators and so at high charging loads the gauge might fail/burn out.

Wiring for an alternator is simply as follows:

• Large terminal to the battery (this can be connected to the live terminal on the solenoid for ease).
• Small terminal to a lamp with a live ignition feed on the other side.

When the engine is off the alternator acts a ground and the warning light illuminates, when the engine is running the small terminal on the alternator is at 12V (approximately) and so the amount of energy flowing through the bulb isn't enought to light it.

You can fiddle with the wiring at the regulator to join it all together but I would be concerned if the main output cable is suitably rated for the load of the new alternator.

 

Thanks for your inputs but the terms large and small terminals don’t help with this type of alternator - see photos below. I’m assuming the ammeter and wiring are sufficiently rated since they’ve been working fine.
Measurements show that the alternator is correctly wired but the signal line towards the ignition warning lamp only shows 150-200mV when the engine is running. Obviously too small to extinguish the lamp.
The following is engraved on the alternator: 8175 12V NEG, 1105 592 Y 94A. Does anyone recognise which is the manufacturer?