Frequently Asked Questions (FAQ).

Realising that some of your vehicles may have been altered by previous owners, here are some original wiring diagrams and images that may help.

Q) Luckily, my car has the original coil and it still works, but it's a part number (Lucas 13C12) that's now unobtainable, therefore a substitute will be needed someday. There don't seem to be many coils up to the job. How does the ReOPUS manage re: coil matching?

A) The board will work with a later coil (e.g. Lucas coil DLB198) as we have tested this extensively. Here is a technical explanation from our board designer:

The reason for the earlier coil having to have a low primary resistance was due to the voltage drop (1.0 volts) across the coil driver transistors and the slow ON OFF switching time of the transistors used. The voltage drop across the transistors also caused them to operate at very high temperatures, especially as it was operating in a +90 C degree environment in the engine bay.

With the voltage drop across the Ballast resistor and coil driver transistors, the coil was operating at less than 5 volts when in the run mode (normally 6.5volts in a conventional system) and this was the reason for the special 5 volt coil with low primary impedance. It was also an attempt to speed up the coil charge cycle, which was slow owing to the characteristics of the original transistors used. This is why the original OPUS was only marginally operating.

With the REOPUS circuit board we have used modern components with a very low volt drop across the coil driver circuit and when coupled with the high speed switching it will operate with any of the coils specified for the V12 engine that used the OPUS system.

It must be understood that the spark is generated when the voltage is removed from the coil, in fact the collapsing magnetic field in the coil generates the spark. With the V12 engine the time taken to re-energize the coil is critical and the old transistors used were not fast when compared with the modern devices.

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Q) I bought a (brand name supplied) aftermarket kit and had problems with the rev counter and ballast pack. The coil I bought from them to match the unit caused problems with the rev counter jumping and I could only get it the engine to run by changing the ballast connections. After reading some adverse reports on this set up, I reverted to my original Lucas 13C12 coil (the one that is no longer available) - it's still going okay, but if the coil packs up I don't know what to do then! Another problem I heard of was the amp (brand name supplied) burning out if the ignition was left on without the engine running. Apparently, if the optical pick up stopped in the wrong place this could happen. Is this is a problem with the ReOpus?

A) There are no problems with the rev counter, ballast pack, or coil. The original ballast resistor has to be used. The standard replacement coil Lucas DBL198 will do fine. The burn out with the ignition left on is also not a problem for our board. The coil driver transistor will stand 20amps continuous on our board.

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Q) My Opus amplifier is not mounted in the "vee" of the engine but on the front radiator crossmember. Will this make a difference to the ReOpus?

A) This will not be a problem as the ReOpus uses the original wiring. Although different cars have differing mounting positions and slightly different external dimensions, the ReOpus will still fit inside the casing. Later Opus units were mounted near the radiator in an attempt to keep temperatures down. Jaguar introduced a version of the OPUS amplifier with longer leads and service agents may have fitted this in an attempt to cure previous ignition problems on an early car. This was an "official" Jaguar modification, so Concours judges should be happy.

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