There have been many suggestions as to why the battery was moved to the boot on the TR8. The most obvious being to offset the extra weight of the V8 engine. This I would entirely agree with, but I can think of other equally practical reasons. After owning an 8 for a number of years it soon became very obvious that it gets very hot under the bonnet - much more so than with the 7 engine - this obviously is not a good environment for the battery. Similarly the V8 really needs a larger battery and there is insufficient room on the existing battery tray. So, with the minimum disruption to the existing electrical system, how do we put the battery in the boot?
Genuine 8s run a cable from the boot directly to the starter motor then all the ancillaries emanate from that point. This is fine on a production car but when it comes to a conversion there are simpler, and somewhat safer, ways.
The solution that I have found to be the simplest is to fit a battery cut out switch in the circuit. This has the dual role of a good anti-theft device and a point from which additional ancillaries can be fed.
First, the battery tray in the boot. Needless to say the original TR8 trays are no longer available, but Rimmers have re-manufactured the early Coupe ones as part of a kit so it is simply a nut and bolt job with the holes already drilled in the floor from the original design. As an aside, one of the reasons why the tray is in the right hand corner of the boot rather than the left is because the boot stay is on the left and if it became detached it could short straight across the battery.. The second way is to construct your own box, but don't forget that an insecure battery is an MoT failure and could cause a fire. As a matter of interest, my first V8 conversion incorporated a plastic marine battery box, round which I fabricated a steel casing securely bolted to the boot floor - the advantage with this idea is that you have a solid box with all the correct air vents and battery cable exits. Whatever your decision make sure it is secure.
To establish the short earth or negative lead at the back of the car, use the earth lead from the battery in the engine bay and connect it to the floor via the threaded hole already available in the chassis rail. Make sure that the threads and surrounding floor area are clean to ensure a good contact and grease the bolt. A dummy run can be carried out with this cable but replace it in the engine bay until the conversion is complete.
Next the live or positive battery lead to the engine bay is required. Again this can be purchased as part of the Rimmer kit, but for those who wish to remain independent, a 13ft or approx 4 metres of 15 sqmm length of battery cable will be required together with the correct end terminations (for those with deep pockets, 25 sqmm cable can be used to reduce the volt drop). This will be sufficient to reach the cut off switch then continue on to the V8 starter motor. A third cable approx 4ft long will be required to connect the switch to the existing TR7 battery cable when the engine part of the conversion is being carded out. The main cable can either be routed to the front of the car by being attached to the under- side of the car with insulated 'P' clips after exiting through the inner rear quarter panel or by following a passage over the inner rear wing, along the inside edge of the inner sill and through into the engine bay via a hole in the bulkhead to the right of the throttle pedal. In both cases correctly sized holes fitted with the appropriate grommet must be used to avoid chaffing. I prefer the latter method as it keeps the cable inside the car but on the downside it requires a lot more work to feed it through the interior trim.