Installing a battery cut-off switch

The position of the battery is a disastrous own goal from BL. Maybe it wasn't so bad in the roadster where you can just lean in, but its a real mess in the GT where access has to be through the door and is obstructed by the seats. Disconnecting the battery is bloody awkward whilst removing it risks a slipped disc or hernia! Quite apart from these considerations there are occasions when you might want to disconnect the battery fairly pronto and its hidden and obscured position makes this all but impossible with resultant risks of combustion. The answer to much if this is to fit an isolation switch readily accessible from inside the car, a trailing charge connection plug and try to tidy up the battery box and clamping system. Here I'm starting with the isolation switch.

I bought a Lucas style 2-pole isolation switch from ebay. Its rated at 100 amps. This type requires a single hole to fit (19.5 mm) although it doesn't come with a nice marked bezel as say the marine switches.

Lucas type switch, I'm not recommending this place- its just a convenient picture!

I decided to fit this into the rear seat kick panel such that I can reach it from the driver's seat. The switch requires 5-6 cms of space behind the panel which is going to be tight so I drilled a pilot hole in my intended spot and tested the free space behind with a probe. Once satisfied that there will be enough room I removed the battery. The switch requires a 19.5 mm hole but has a flat section to prevent it turning. You cannot therefore use a 19.5 drill, so I bought an 18mm drill which could be used through the folded seat to reach the kick panel.

Drilling through the seat gap- take care not to rub the fabric

The hole was then enlarged using a flat file at the top and a round file to expand the hole the rest of the way round.

Flat file to make flat on top of the hole and ensure the switch will fit in the vertical position for "on" and horizontal for "off".

Round file to enlarge elsewhere

I tested fit from the front as its much easier than poking the thing up from underneath. 

Testing fir from inside the car

Once  the hole was large enough I fitted the leads to the switch before mounting it, as once again access will be poor once fitted. I have a cable crimper and so could make cables any length I want but if you want to do it this way using pre-made cables you will need two 60-70cm lengths with appropriate terminals.  I decided to fit the switch in the earth wire which is probably not the best choice; it means that I do need to lengthen the cable run by about 1.5 m and this will increase resistance to current flow. However, I have fitted a hi torque starter which draws less current anyway and the risk of creating additional live junctions with  potential shorting to the chassis I felt outweighed this concern. 

New battery cables connected- rubber boots to protect terminals

Switch showing the adjustment thread- adjusting nuts removed.

I could then fit the switch into the panel and tighten it into position. It comes with two ring nuts on the stem. The kick panel metal is sandwiched between these and by adjusting the nut position in theory you can move the switch fore and aft in the panel. As I said above, I was concerned at the lack of space so I just used this on the fully down position.

Switch installed

Routing the new cables should ensure that they are held well away from the battery so that they don't obstruct what little space there is for removal and refitting. I drilled 3 pairs of holes along the top of the battery box to insert cable ties to keep the cables tidy and guided them to the battery negative and the original chassis earthing point. 

Sorting out the new cable routes. Note the three pairs of holes drilled for the cable ties, and also spray primer to seal the raw edges on all holes I made.

I attached a quick connect earth terminal to the battery lead. I don't like using these as they can pull off, but as I'm using a generous length if cable,  its curved gently and shouldn't be under any stress.

Battery cables positioned and tied with cable ties.

Finally I made a hole in the carpet and soundproofing for the switch and fitted the control knob.

Switch installed

Before closing up the battery I altered the position of the battery clamps. I hadn't acquired a battery clamp when I got the car (MOT failure) so I bought one from MGB Hive. However the struts on this were too short to attach at 45 degrees across the battery and would only fit vertically down- which didn't really clamp anything at all. I drilled some new holes halfway across the battery carrier so that I could get some angle on the struts and this did improve security of fitting.  I also attached a fused trailing lead with a quick connect 2 pin connector as supplied by Oxford for use with their battery chargers. All this should mean that I don't have to open up the battery compartment nearly as frequently as before!