Remote Control Battery Main Switch

It would appear obvious that a battery main switch, which is located somewhere in the dash, does not really make sense in cases, where the battery is in the rear trunk, since this does not protect against shorts of the mains cable (coming from the rear) to the chassis. This rear arrangement of the battery is quite common in classic cars, like front engined Lamborghinis, Alfa Montreal and presumable at least some classic Ferraris.

My proposal to this problem is the remote battery switch PN7700 available from Blue Sea Systems and distributed by well sorted marine suppliers. It is a bistable solenoid switch that switches under a load of 500+ A. It has a manual operation control button, but the main feature is the remote control function. For this purpose a separate circuit needs to be contacted directly to the battery with own fuses (10A and 2 A), which should be placed directly by the battery terminals. The solenoid contacts are completely potential free, so that you can decide, whether to switch +12V or ground (I chose the latter). The solenoid switches from one state to the other upon a short puls through a control line (7A for the 20 ms when changing state). Otherwise there is absolutely no power consumption (I tested for that as a matter of precaution) by the remote control circuit, zero µA.

Often there are convenient spaces for positioning of the switch. Somewhat challenging was the Espada (see photos, please disregard the badly placed trim mat). In the first photo it looks almost like the original configuration, wherein a small box made of resine serves as internal cover for the rear lamps. In second photo the (original) trim placed on the switch, that replaced the cover, is removed. You can see the manual operation button. In the third photo a replacement battery cover is evident; I did not want to saw out a piece of the factory orginal battery cover (which now rests on a shelf).

You need a switch with a configuration like window switches, since the solenoid needs an impuls only to flip from one state to the other. You can e.g. take an original window switch and place it at a free position in the dash (i.e. a place for a switch not optioned for originally). Then it will look as if some original switch and be convenient to operate.

P.S.: Do not open the main switch as long as the engine is running, because this will kill your alternator. In case of an emergency first kill the ignition, then the mains.
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I believe not (obviously ). I some race car categorys it is obligatory to have a battery main switch in reach of the driver, presumably also not a solution looking for a problem .

First, if there is an electrical hazard, you simply push a button on the dash (or elsewhere in reach) and everything is shut down. I am talking of classic cars, wherein rarely the complete wiring has been renewed, thus having wires being 40+ years old and in part being thermally and mechanically exposed. Same in case of a fuel leak or accident. No need to stop, rush to the rear and detach the battery. Or pull one or more fuses (does someone know them by heart?). Instead of having to rewire the mains for fitting of a manual battery switch in the dash (ugly!) or footwell (battery and starter typically are on the right side of the car, the driver on the left), the remote switch just needs rewiring directly at the battery and additional control wires to the dash button, placed whereever one wants, only.

Second, in classic cars with clap-hand wipers these sometimes tend to jam in the least convenient moment. Espada and Jarama are well known for this phenomenon. The wiper motor still gets plenty of amps, even if you operate the wiper switch to "off" (return function). Shortly after jamming the motor will start to overheat, since it draws a lot more of current than while rotating. Only option is to pull the right fuse or battery terminal asap, then unjam the wipers (and continue with the drivers wiper only after having put back the fuse etc.). You will become very wet . With the remote switch, a push on the button, peace of mind, a quick jump out for unjamming/detaching and thats it.

Furthermore, if you work on electric car components or circuits (or mechanics near such components), it is very convenient. Push "off" on the dash button, do what you need to, push "on", test and continue. I have recently renovated the complete electric wire contacts under the dash (dash removed) and rewired quite a lot. It was extremely convenient to work on a circuit and to test it, without having to run back and forth to the battery all the time.

Finally, most classic cars still have the factory original main line from the battery to the terminal/starter in the front engine compartment. In case of the Jarama going through a sill. Or at the sill and under the glued sound deadening material in the Espada. You can either replace this as a matter of precaution, or place the remote battery switch directly near the battery. Or both .

Post-finally , a person not knowing which button (e.g. a factory original one) to operate will not move the car, at least not quickly.