Converting to an Alternator and Negative earth

[cass3958]

I have just spent the last week converting my S Type from the old dynamo with positive earth to a new alternator and negative earth.

In the end it was an easy job but working out the wiring circuit from the instructions given by the company that make the alternator was hard work.

The alternator is made by Dynalite and is basically a new alternator in the body of the old Dynamo with the take off on the back for the power steering pump and it is called a Dynalite. Four years ago when I rebuilt my car these were £650 but have now come down to £145. The reason I decided to change over was made for me in a way as I had previously changed to an electronic ignition system but this was positive earth sensitive so it made no sense to change the distributor and Dynamo. But as I said the changeover was helped by my electronic ignition breaking down on me so as I needed a new electronic distributor I went the whole hog, changed both and went negative earth.

The reason the job took so long was that I first had to diagnose that the old positive earth distributor had packed up and whilst doing this I found a fuel leak from one of the hoses below the carburettors and the only way to get to this hose which feeds the AED was to take the carbs off. Not an easy job with the engine in situ but once out it allowed me to clean the engine bay and replace the fuel hose. I removed the bonnet to do this work as it gives you so much more access. The battery also came out to give me room down the side of the carbs. Whilst fixing this fuel leak I ordered the new parts I needed to change over to the Dynalite. When the new Dynalite arrived it looked identical to the old Dynamo. All the fittings for the brackets and power steering pump are identical, you just need to swap the front pulley and fan blades from old to new and bolt the PAS pump to the back of the Dynalite. The old Dynamo weighed in at 25lbs where as the new Dynalite weighs a mere 8.5lbs

Back to the wiring. The instructions from Dynalite say that you no longer need the regulator control box and you just need to run a wire to the ignition switch from the large terminal on the alternator and a second wire from the small terminal to the ignition warning light. Sounds simple and it was in the end but you have to trace all the wires first by doing continuity tests to see where they all run and which was which by paring back some of the wiring loom in the engine bay. The Dynalite instructions make no mention of how to rewire the Amp meter, the fact that we have a solenoid under the bonnet and a push button starter or which wires on the control box do what. So I have done the tests and this is how the original circuit works on the S Type.

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 negative earth to make the Amp meter read correctly.

The right hand connector on the Amp meter goes to the ignition switch and on to the solenoid on the bulkhead. This is where it gets a little confusing but on the solenoid there are three terminals. As you look at it from the front left wing the large terminal on the right goes to the starter motor. The large terminal on the left goes to the Battery and has two smaller wires coming from it on my car which has an Auto box. One wire goes to the Auto box to power the Auto box safety switch the second wire is coming from the ignition switch. I assume this is a two way wire and what I mean by that is that it allows power to go from the battery to the ignition switch on start up but when the dynamo is running it allows power generated from the dynamo to run the other way and to trickle charge the battery. Then in the centre at the bottom is a small single wire connected to a separate terminal.

So when the key is turned the wire on the large left terminal of the solenoid takes power from the battery to the ignition switch. When you push the starter button power is diverted briefly through the starter button along a small wire to the small centre terminal on the solenoid which acts like a switch and allows power to jump across the solenoid from battery to the starter and the car like magic starts.

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. At this point I pared back the wiring loom and removed all the extra wires and the Regulator box from the inner wing. I might put this back as a dummy to keep the original look but will have to tidy up the wires with some dummy terminal connectors. 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.

OK Dynalite all connected up and at this point I had to change all the earth connections over on the car, which are listed below.
1. I disconnected the radio completely as I have a positive earth original radio which I never use so no hardship removing it. Some radios have a switch on the back which allows them to be switched from positive to negative earth but mine hasn’t.
2. Both SU fuel pumps need to have the wires changed over. Just swap the wires between the terminals.
3. The clock in the speedo needs to be disconnected. If you want this to work on negative earth you need to send it off to have it changed, Mine does not work anyway like so many other Jaguar clocks so again no hardship.
4. There are two wires on the fan motor on the bulkhead which you do not need to swap as one is for high and the other low but the direction of current does not need to change.
5. As stated before the two wires on the Amp meter need swapping or the Amp meter will be registering discharge when it should be showing charge.
6. The water bottle motor leads needs to be swapped to get it to squirt rather than suck.
7. If you are keeping your original distributor and coil then the leads on the coil have to be changed around. In my case I was changing the coil with the new distributor.
8. Finally you have to reconnect your battery so negative is your new earth.

In my case I set the static timing turned the key and the car started first time. Job done.

I hope this is of help to someone else who is contemplating changing over either from positive earth to negative or changing over to a Dynalite alternator. Now I can change my dash bulbs to LED and charge my phone. Another 1st world problem solved.

[Jose]

wow what a job! But congrats for getting it done right.

So how does it work now? is the ammeter reversed? I have heard from others that it was showing reversed.

also have heard that the red Generator warning light stays ON.

As to the clock, I had mine converted to digital and Negative Ground by wizard Mike Eck of Jaguar Clock. Has not failed yet.

www.jaguarclock.com

[cass3958]

Works fine not had a problem with it Jose.
By changing the wires over on the back of the Ammeter it now works correctly showing charge when ever the car is running unlike with the Generator which would only charge when you drove the car over 1500 rpm not on idle.
As for the red light if it is wired again as per the write up the red light comes on when you turn the key and once the engine is started it goes out.