There are few components that make up the charging system on the TA. There's a dynamo (generator), a switch allowing the choice of three amperages passing from the dynamo to the battery. (Summer, Winter and full charge when the headlights are on) And between the dynamo and battery there's a cutout which 'cuts out' the circuit between the two when voltage drops below a set level.

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Dynamo/Generator

The photo above shows the end plate of a TA dynamo with the three brush set up. The carrier for the smaller (3rd) brush is attached to a circular ring which is movable around the center of the plate. Movement of the plate, one way or the other, changes the amount of current (Amperage) the dynamo is putting out.

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CJR3 Cutout

Usually with 'regulated voltage' charging systems the state of the battery determines the amount of voltage supplied by the dynamo/generator. This is not the case with the TA/TB charging system. Here the dynamo output is constant. It uses a CJR3 cutout with two additional resistances inserted in the circuit in conjunction with the PLC switch to select a voltage which is then sent to the battery.

CJR3 Terminus Guide

A cardboard/paper guide such as the one above is usually found underneath the wiring hook-ups on the back side of the CJR3 Cutout. It helps to simplify harness hookups from the dash and other points to the fused terminals on the front. I would presume these to have originally been placed on all TA CJR3 cutouts. I found mine quite oily after 68 years in the engine compartment but it cleaned up enough to read the printing.

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Lucas PLC High/Low Charge and Lamps Switch

In the Low (Summer) position there are two additional resistances in the CJR3 cutout for the field circuit. When switched to High (Winter position) there is only one additional resistance in the field and selecting it sends a greater amount of charge (amps) to the battery.

The greatest amount of charge is needed when the headlamps are used and swinging the lever to Head sends the maximum amperage the dynamo is capable of creating into the charging circuit. That rate is determined by the placement of the adjustable third brush in the dynamo.

The diagram above illustrates how the switch works (looking at it from the back). The ignition On/Off contacts are in the center while the outer connections are for lamps and charging circuits.

And the illustration below might help understand the circuit using a CJR3 cutout and 3 brush dynamo.

Diagram of the Third Brush and Charging Circuit
The third brush can be moved to vary the output amperes.

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CJR3 To RF95 Conversion

Converting A 3 Brush Generator To 2 Brushes
For various reasons some owners have abandoned the 3 brush dynamo/generator with CJR3 control box and replaced these with a more modern charging system using a 2 brush dynamo and RF95 voltage regulator. After the War Lucas realized the advantages and published a small technical brochure detailing how to accomplish this using then-modern-day components. One of those advantages is that later 2 brush dynamos delivered more amperage than the 3 brush variety. Click the image above to read the Lucas PDF explaining the process.

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THE THIRTY LIGHT

A green-lensed Thirty-Light is also incorporated in the electrical system being activated by a brass or copper contact inside the speedometer. These were also used in the TB and into early production of the TC. The reason for the Thirty-Light was to warn drivers that they were approaching the maximum speed limit enforced in many towns and cities throughout Britain in the pre war years. While it is interesting and amusing to watch it come on at about 20 mph and go off just over 30 a few modern-day TA owners have removed the wire leading to the speedometer and rewired the light for use as a Turn Signal indicator.

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THE STARTER MOTOR

The correct starter motor for the TA was a Lucas M418A A84 with the cable operated solenoid mounted on the side as shown in the examples above.

A MODIFICATION
Although not original to the T-ABC some owners have replaced the pull start knob and wire with a push button switch connected to a remote electric solenoid. I've heard two reasons for doing so; No longer are you pulling up against the wood dashboard as we do for the Choke and; Because they were period-correct for some automobiles and were exchanged for sheer ease and convenience of starting up.

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ORIGINAL WIRING DIAGRAM

From the Blower Workshop Manual

This diagram above follows the correct color code for Home models with one dipping headlight. Click the image to view it larger.

The TA Wiring Harness / Routing

There has been some controversy over the route that the Battery-To-Battery cable originally took. Some owners, having two 6V batteries, have taken the cable over the top of the prop/drive shaft as did the MGA and MGB.

However there is strong evidence that it went underneath the prop shaft and attached to the chassis with P-clips.

There is at least one factory photo of a TA chassis, without the body tub but with batteries in place, where the connecting cable takes the lower route. In the photo (above left) the short Positive Earth cable is still attached to this chassis. I also have another photo of an unrestored chassis which still has both the longer, battery-to-battery cable and this Pos. Earth cable still attached. The photo above (right) is the route used by a well known pre-war MG restoration firm for their TA/TB Tickfords. Notice the two P-clips retaining the connector cable.

Dash Wiring

TA wiring is rather simple and available with original design cloth wrapping from several sources in the States, UK and Australia. One can also DIY your own but be prepared to spend a bit of time. A number of us have converted a TC harness for our TAs and most will tell you that it's easier and perhaps cheaper to have one made. I happened to have a Moss TC harness left after selling a car and decided to try it. It also included wires for turn signals which I wanted. The color codes are pretty much standard for British auto wiring and essentially the same between TA and TC. The big difference is that the Control box (TA) and Voltage Regulator (TC) are on different sides of the cars else it might have been usable as it was.. but no. After removing the original TA harness I labeled and measured the various groups of wires then unwrapped the TC harness and laid them out so as to match the needed TA lengths. Gathering them into groups, like a tree trunk with branches at the proper length, I reused the plastic non-sticky tape from the TC to form the basic harness. Once all the 'branches' were snuggly covered with the plastic tape I used black basting tape from a sewing shop and wrapped the harness again covering the plastic for a nicer look. There were a couple of difference I noticed in the new TC harness vs. the old original wiring. One was that the new, individual, wires didn't seem as thick, not as heavy gauge as the old, and that the new wire is plastic/vinyl coated (with color codes) where the old was rubber(?) then cloth covered. The cloth cover having the color code. I was concerned at first with the new wires seeming a lighter gauge (and there's not a lot of difference) but part of that may be in the rubber/cloth covering of the old stuff and also figure if they work for a TC then...! It sounds quick and simple here but it took quite a lot of time measuring, remeasuring and confirming the codes before I was confident I had it right. I did not replace the small original Dash Wiring Harness as it was in good enough condition to reuse.

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For a hybrid TA wiring diagram using an RF95 Control Box and two-brush dynamo, double filament headlights, turn indicators and other accessories see Ian Linton's rendition here. Interesting reading and a comprehensive article on a number of electrical modifications he made when he restored TA3120. Bob Butson has also written a very informative article on his use of LEDs when restoring TA0844. Once again, John James' online magazine, Totally T-Type 2 comes to our rescue. Read Bob's article here.

Here's the circuit diagram from the TA Owners Manual showing the route taken when wiring double filament headlamps. The connections are made on either side of the Headlight Fuse. Click the image to view larger.

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THE TA DISTRIBUTOR

A Lucas DK4A distributor came as original equipment on our cars. It uses a micro-adjustor underneath to fine tune the timing.

The distributor with cover removed

- Instructions From The Workshop Manual -
The following parts of the distributor require lubrication:
1. Distributor Shaft: Add a few drops of thin machine oil through oiler provided about every 1000 miles.
2. Cam: After the first 500 miles, give the cam a smear of engine oil every 3000 miles.
3. Cam Bearing: About every 3000 miles, withdraw the moulded rotating arm from the top of the spindle by pulling it off , and add a few drops of thin machine oil. Do not remove the screw exposed to view, as there is a clearance between the screw and the inner face of the spindle through which the oil passes to lubricate the cam bearing. Take care to refit the arm correctly and to push it on to the shaftas far as possible, otherwise there is a risk of tracking and burning of the moulding.
4. Contact Breaker Pivot: Every 5000 miles place a spot of oil on the pivot on which the contact breaker rocker-arm works.
5. Automatic Advance Mechanism: About once every year the moving parts of the automatic timing control must be lubricated with a good grade engine oil. To render the control accessible, remove the distributor moulding and lift off the rotating distributor arm, then remove the contact breaker moulding by withdrawing its two securing screws.

Using The Micro-Adjuster
Sitting under the distributor and often misunderstood is the Micrometer Timing Adjustment. The Workshop Manual says that; 'With a clean engine, and using first grade fuel, the micrometer scale should be at "O" before timing. The final setting can be made by use of the micrometer adjustment after running the engine. If the firing is found to be slightly too early or too late, adjust the knurled knob until the best engine performance is obtained. The adjustment should not be altered by more than one distributor degree at a time (one division on the scale is equivalent to two distributor degrees or 4 degrees on the crankshaft). I believe it is marked + on one side and - on the other so you know whether you are Advancing or Retarding the spark. And you should be able to feel the clicks.

Electronic Ignition
Kits are available online for DK4A distributors with Positive Earth. However most everyone agrees that if you do convert to electronic ignition you best keep a plate with points and condenser and rotor button in the toolbox because when these do go out there's no amount of fettling that's going to get you going again.

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Capacitor/Condenser Exchange

Several T series owners have reported capacitor/condenser failure in recent years. As our cars get older it’s not unusual to have the original capacitors begin to break down and need replacing but an alarming number of new capacitors fail right out of the box or in a very short time. Good reason to keep a spare in the tool box. The Distributor Doctor in UK is said to have very good quality capacitors and also sells Red Rotors. Their ‘Red’ rotor buttons are an improved version to the newer ones being sold which use a rivet to hold the contact on. Below is an example of a NOS Lucas capacitor (originally intended for an MGB or Midget) which has been hidden inside the distributor cap replacing the long original-type.

As can be seen in the photo a metal 'bridge' had to be added for making the contact at the rear of the newer capacitor with the base of the distributor. The pig-tail at the front required another screw and nut. When mounting a modern capacitor/condenser inside the distributor using extra screws and nuts as shown here make sure they're tight! Although the engine might stop before damage inside took place (if a screw came loose) still, you don't want that gamble. And remember, they do not have to be mounted inside the distributor to work.

Another Approach
Capacitors similar to original are available and can be sourced from Graham Brown of JB Vintage Spare of Croydon via E-Bay. Brian Rainbow may have the best method of all. He carries a spare distributor base with new Graham Brown capacitor that as been pre-fitted, gapped and checked rather than carrying spare points and condenser. This can be replaced road-side much easier than fiddling with the individual items.

You can read more detail about this and his description of a quick and safe way to remove/replace your distributor in Issue 14 of the Totally T-Type2 found here.

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A VACUUM ADVANCE FOR THE TA

There's a very interesting article here written by David Heath in Issue 34 of TTT2 explaining how he modified a Lucas 59D4 distributor for use in his TA.

The 59D4 is a vacuum advance type distributor as found on a number of Metro and Minis and once reconfigured for a TA requires a considerable amount testing before turning loose on an MPJG engine.

I corresponded with David looking for more information about modifying a 59D4 distributor for my own use. He generously offered help and advice with various issues I had as the project progressed.

After acquiring a distributor I modified the mechanical advance and also replaced the drive gear on the shaft. These gears are now available new from the Distributor Doctor in UK. He can also supply (or they can be sourced online) a set of assorted Lucas springs needed for tweaking the advance curve in the final stages of development.

59D4 with DK4A Drive Gear Installed (vacuum unit removed)

I made all the mods to the distributor, made a bracket to hold it securely in the block and even modified a spare intake manifold to accept the vacuum line. I ran it for a couple of hundred miles in mechanical-advance-only configuration and at that point my curves were good enough to try out the vacuum advancing but would still require a considerable amount of time selecting the correct set of springs so as not to burn holes in pistons.

This is best done, as David explains, on a 'rolling road' where the car is stationary and mechanical adjustments such as springs on the weights, carburettor needles and even octane ratings can be tested easily without starts, stops and working along the roadside. Without a proper rolling road I got cold feet and went no further than an initial test to see that the vacuum advance was indeed working.

But I can say this for the 59D4, it is a very good distributor!
Perhaps because my DK4A is old and maybe a little loose in the bearings and the 59D4 is newer and possibly tighter it fires more accurately than the original and I'll certainly be keeping it.

It was a very interesting project that I'd recommend for anyone wishing to learn more about timing advance curves and the workings of a distributor whether you follow through to a fully working vacuum advance distributor or not. And because a good used 59D4 is far less expensive than replacing a 'proper' DK4A with a little work you'll have a dependable and very serviceable spare.

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BETTER TIMING MARKS

One of the essential needs in setting up the vacuum advance distributor is a reliable means of viewing Top Dead Center during dynamic timing. The factory markings on the crank pulley and timing chain cover are about worthless unless you have the radiator off. I'm sure this has been a sore point for lots of us wanting to use a strobe light for dynamic timing. And in fact it's impossible without adding marks of some kind.

One owner I spoke with told me that he had used a wire marker attached to one of the engine strap bolts then painted degree marks on the pulley. Another suggested putting marks to represent TDC on the pulley and timing case housing over on the left side of the engine.

I used a heavy wire (clothes hanger!) and attached it underneath one of the bolts securing the timing chain cover. My greatest concern was that it might not be stable, would vibrate, and not allow an accurate reading with the strobe but was pleased (maybe even a little surprised) when it remained steady with varying engine speeds.

Timing Marks

The photo above was taken before adding two more white marks (at 5 and 10 degrees BTDC) on the pulley near the wire marker.
π x D will give you the Circumference of your pulley. Divide that by 365 to find the length of each degree.

Notice the white mark at the back of the pulley. This photo is a little confusing because that large nut is holding the dynamo to the upper mounting bracket. In the photo it looks like there are 3 lines. (That short vertical portion is actually on the front of the seal housing.) If it could be viewed from directly overhead that line at the back of the pulley would line up perfectly with the white line on the top of the crankshaft seal housing. This is a good example of what you are faced with when trying to view TDC from the side of an MPJG engine. And the reason for creating better marks for dynamic timing.

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