Jan 162014

There’s been a dramatic drop off in progress with the restoration in the last month or so. Partly due to the horrible winter weather, resulting in an apathy to venture out into a cold, dark garage!

In the meantime, attention has turned to sorting out bits and pieces that could be worked on indoors, although it gives an excuse for the gratuitous inclusion of some photos of the main reason for the lack of headway … a diving trip in warmer climes!

Progress is delayed due to a spot of diving …. with some immature 6m Whale Sharks

Back to the plot …..

Several years ago I’d come across an owner’s restoration of a ’63 OTS where they had redesigned the looms to their own specification, incorporating relays for the headlight circuits. The addition of relays made good sense, as they remove the main current bearing wires from behind the dash area, but I wasn’t convinced about having bespoke wiring looms made.

Deviating too far from the original wiring looms would mean that, if I subsequently encountered electrical problems, I’d be on my own as it would be hard seeking accurate advice from fellow owners. There was also the fear of overlooking a critical wire when the looms were made up or getting the length of one of the wires slightly wrong. It would be an expensive mistake to fix!

So the idea of adding relays was shelved and a new set of standard looms purchased. Fortunately this proved to be the right course of action. At the time, I hadn’t spotted the wiring diagrams I was using weren’t correct for my car. They didn’t have the changes in circuitry covering the introduction of the ballast resistor into the ignition circuit.

Rather timely, as I was starting to look at the lighting and bonnet electrics, an excellent write up of a headlamp relay modification was covered on the E-Type forum. The installation is very discreet with the relays being mounted out of sight behind the LHS ‘sugar scoop’. The only visible sign of the modification is the main power feed, taken from the alternator B+ terminal.

The downside of tucking the modifications within the bonnet is that it will be much trickier to maintain if something fails. The headlight bowls and possibly the indicators would need to be removed to gain access.

I had some spare repro 6RA relays so all I needed to purchase were some suitable coloured & rated wires and two in-line fuses. I also decided to install Halogen headlights at the same time.

The circuit diagram shows the planned wiring modifications, with the additional components labelled in red.

There are two spare terminals in the 8-pin bonnet plug, which were originally for the bonnet mounted horns found in the earlier cars and, I believe, the provision for optional extra spot/driving lights.

One of these spare terminals was used for the single high load wire running from the alternator B+ terminal to the 10-way connector in the bonnet. (It’s much easier to take a supply from the B+ post rather than travelling all the way back to the battery.)

I managed to feed the wire into the PVC sleeving to the bonnet plug so the only visible sign of the installation in the engine bay is a single sheathed wire running from the alternator to the bottom left of the picture frame, which has been cable tied to the existing loom.

From the bonnet connector, this feed splits in two to provide the 12v supplies to the dipped and the main beam relays. The relays have a double spaded terminal for the switched output, so the wires to the left and right hand lamps were connected directly to the relay.

Wire and fuse ratings
The Halogen dual filament bulbs are rated as 55W/65W at 12v so the dipped and main beams for each bulb will draw around 5.5 amps and 6.5 amps respectively (assuming a charging battery voltage of 14.3V).

Normally only one set of the filaments are on at any one time. However the worst case is when the main beam is ‘flashed’ while the dipped beams are on. Even though this should only be for short periods of time, I thought it prudent to assume the maximum current required for both headlamps would be 24 amps (2 dipped @ 5.5A each and 2 main beam @ 6.5A each).

Therefore 44/0.30 cable, rated at 25 amps, has been used for the supply from the alternator rather than the 28/0.30 cable suggested in the forum write up. Inline fuses have been used for the connections to the two relays. Their wiring is rated at 30 amps which is more than enough, although they have both been fitted with 15 amp fuses as the expected loads are 11 amps dipped and 13 amps main beam.

Using two fuses should ensure that a blown fuse won’t result in the complete loss of lighting!

The original wiring for the dipped beam (Blue/Red) and main beam (Blue/White) will now just be used to switch the relays. The coil resistance for the 6RA relays was measured at approximately 83 ohms so the switching wires will now only need to carry around 0.17 amps. Therefore the dash mounted fuses 1 & 2 have also been replaced, by 0.25 amp fuses.

As the whole bonnet area had been coated in copious amounts of Waxoyl, I also fitted some PVC sheathing to the bonnet loom in an attempt to keep it clean. I just need to tidy up the cabling when the headlamps are fitted.

Dec 092013

As with many other cars of the period, E-Types use Lucas 6RA relays to control the power supply to the various electrical ancillaries, specifically those that draw larger currents. The obvious benefit of using a relay, an electrically operated switch, is it allows a high current circuit to be controlled by an isolated, low current circuit.

This enables all the wiring handling the highest currents to be located within the engine bay and controlled by low current wiring routed from the dash area. Removing the high current wiring from the dash reduces the potential fire hazard.

So it’s odd why Jaguar didn’t use relays to control the main and dipped headlights. The addition of headlight relays is another popular modification which I’ll be making in due course. The mounting of the horns was relocated from within the bonnet to the picture frame during the production run of the S1 4.2. This has freed up a connection in the 8-pin bonnet plug which can now be used for the high current feed from the battery and the relays can be discreetly located behind the headlamp sugar scoop.

Four types of 6RA relays are used in the later S2 cars (those with the ballast resistor):
Terminals layout for the Lucas 6RA relays - applying 12volts to the W1/2 terminals switches the relay, connecting the C terminals

  • Alternator Relay – 33209F (SRB121) : 20A 4 pin
  • Starter Solenoid Relay – 33231E (SRB400) : double contact 5 pin
  • Cooling Fan Relay – 33232E (SRB501) : 3 pin
  • Horn Relay – 33252E (SRB111) : 20A 4 pin

Note: the SRB numbers are the modern replacement product codes

Internal wiring layouts for the Lucas 6RA relaysTo the right are diagrams detailing the external terminals and internal wiring for the four 6RA relays used in the S2.

The difference compared to the earlier cars is the starter solenoid relay has double contacts to enable it to provide power to the starter solenoid as well as bypassing the ballast resistor while the starter is in operation. All are simple electromagnetic type relays, which are ‘normally open’.

The various relays were all working fine but were showing the effects of decades of exposure to the elements and looked very scruffy against all the restored components.

The relay covers are only crimped in four places so it was possible to carefully undo them to enable the covers to be removed. These were dipped in a mild citric acid solution overnight to remove the remains of the zinc plating before being re-plated.

With the exception of the 3-pin cooling fan relay, the W1 and W2 terminals are used to energise a coil winding which has an iron core at its centre.

In the energised state the coil produces a magnetic field which draws a sprung, iron armature towards the iron core. In doing so a contact at the end of the armature (C2 terminal) makes a connection with a fixed contact, the C1 terminal or the C1 & C4 terminals for the double contact relay.

The 3-pin relay lacks a W2 terminal because it is designed for applications where terminal C2 is always connected to 12 volts. Internally the C2 terminal is also connected to the coil winding and so acts as the W2 terminal as well, delivering 12 volts. The coil winding is therefore energised by grounding terminal W1, resulting in the switching of the relay.

All that remained was to tidy up the electrical connections and re-crimp the covers back in place.

Ignition Switch
As I was sorting out electrical bits and pieces, attention turned to the Lucas ignition switch, which is marked 157SA 39415A. I’m not sure if this has been replaced at some stage but the terminals bore no correlation to the wiring diagrams and had intermittent connections when tested with a multi-meter.

The terminal connections on the wiring diagrams indicate:

  • 1 – Brown : supply from Battery, under permanent current
  • 2 – White : under tension only after ignition switch is on
  • 3 – White/Yellow : via starter solenoid relay, delivers power to the starter motor

Therefore, when the key is in position II, terminals 1 and 2 should be connected and when the key is in position III, terminals 1, 2 and 3 should all be connected.

To achieve this with my 157SA switch, the White/Yellow wire can only be connected to terminal 1. The other wires using terminals 2 and 3, in any order. I decided to take the switch apart to see if it was possible to ‘correct’ the terminal connectivity and address the intermittent connection problems.

The switch can be split in half by gently prising the retaining tabs outwards. The tabs are made of pot metal so I wasn’t sure they would survive the operation.

Inside the copper contacts were heavily ‘gunked’, which was the most likely cause of the intermittent connections, so they were cleaned up with good old Brasso.

The key lock engages with a nylon disc within the switch, which therefore rotates as the key is turned. On the underside of the disc is a sprung ball bearing which locates in dimples to differentiate the key positions and a spring which returns the key position from III (starter motor engaged) to position II when the key is released.

There’s no ability to change the terminal connectivity so I’ll just have to adjust the terminal wiring accordingly.