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MG MGA - extending battery cable

Recent discussion on 12 volt batteries and the poor performance of my aging 6 volt batteries plus the cost of replacement has finally persuaded me to change to a 12 volt system. I'm ok with the battery type (063) but does it make sense to put it behind the passenger seat to balance the weight with one driver? I intend to use a purpose made subframe within the existing battery carrier as per archives but this means extending the insulated live cable. Whats the best way of extending the cable so there's no volts drop across the joint? Would a sleeve suffice say 30 mm long with one or two screws at each end or is this inviting problems later on? I may have to extend the cable even if the battery goes behind the drivers seat if it goes 'long way on' and the -ve terminal is too far away.
J H Cole


I would not have thought that one battery would make that much of a difference to weight distribution.

Nevertheless, a useful way of extending your cable would be via a cut-out switch. You could mount it on the wooden vertical board behind your driving position. You connect the existing live cable to one terminal and then the extra length from the other terminal to the battery. Having an isolator like this in the circuit makes sense for our ancient wiring systems. It's easy to isolate the electrics when doing work on the car and it's an extra anti-theft device, since you can take the isolator key with you when you park. The switches are available in the likes of Halfords etc.

Steve Gyles

Obviously, the best would be to replace the entire cable with a longer one but that is probably not worth the effort. Even if you splice an extra length of wire on you will still have the same number of joints in the wires as you have now with the two 6v batteries. If it were mine, I would get a tinned copper tube butt splice and adhesive shrink tubing to cover it. Best to solder it on. Strip and clean and tin the ends of the wires, heat the center of the splice and apply solder where the wire enters the splice, just like soldering copper plumbing.(be sure to slide the shrink tubing on the wire before joining the two, voice of experience)Would take a very large soldering iron so probably use a torch.

Took me a minute to figure why you would need to lenghten the cable to connect to the passenger side, but then realized where you are. Also, since you call the hand held thing you use to light up the night a torch, what do you call the thing with fire coming out the end that plumbers use to solder copper pipes?

Jeff Schultz

Jeff - soldering the wires makes sense - and that would be a plumber's blow torch over on this side of the pond .
Cam Cunningham

"Even if you splice an extra length of wire on you will still have the same number of joints in the wires as you have now with the two 6v batteries"

Not necessarily true. Going to 1 battery elimintes the wire/clamp junction in 2 places and the clamp to battery terminal junction in 2 places; for a total of 4. It is replaced by the one (maybe considered 2)soldered splice junction, a much better long-term reliable connection. Brazing the splice can also be used. It is a common practice in HVAC work and in manufacturing large transformers.

If you are replacing thejunction with the cut-off switch, then you regain those 4 junctions plus the internal switch contacts too. But arguably, they are better reliability too since they are away from the acid fumes of the battery.

BTW, found when soldering old wiring and pipes where the old copper has oxidized and corroded, it is difficult to get a good soldered joint. The solder just balls up and lays on top of the oxidized wire instead of wetting to the copper. The flux in the wire is not agressive enough to work properly. I have found that a commonly available cleaner for toilet bowls that does a wonderfull job in freshening the copper. It is called "the Works", thick formula. It is basically 16% hydrogen cloride. It leaves a nice pink hue to the copper. It must be rinsed off completely and dried before soldering. Maybe baking soda and water would deactivate the acid too.
Chuck Schaefer

I agree with steve, I dont think having 1 battery behind the driver would make that much differance and as far as having to extend the cable for the lenth of the 12v battery go's you can get a 12v battery to fit the existing cradle, I have just bought one online its size is 175mm x175mm by 190mm high 40 Ah and 40 diliverd to the door, and that would also laeve you with a nice little slot to fit a small tool box or something, Vin
Vin Rafter

Doesn't it depend on how heavy your wife is?
Lindsay Sampford

Also called a "blow lamp". Now that is a quaint term.
P. Tilbury

I purchased a new length of battery cable (marine stores sell welding wire which is more flexible) for $30 and replaced the whole thing to get an extra foot or so that I needed.

AJ Mail

Who dod you buy your battery from please? Thanks Graham
Graham M V

Vin, I've just read the Dec 09 addendum ET203 on Barney's site for single 12 volt batteries and he details two batteries that will fit in the existing carriers. They are both 175x175x190 either 'Advanced 002' or a 'Varta'. Is yours one of these? This would save making alterations but I think one has to accept a lower CCA -cold cranking figure of 360 -390 compared with say a slightly larger battery that gets into the 400's. If the original 6 volt batteries had a CCA of 300 does it mean that combined thay gave 600 CCA - potentially a lot of power to draw on? With my MGA its that next day cold start in very cold weather that gives me trouble. Once the engines going I never get a problem for the rest of the day. I suspect the CCA figure is often more important than a slightly lower A/H rating.
J H Cole

I have the larger 063 battery fitted. It is a very common battery around the world and is probably the cheapest battery to buy. Many thousands of modern vehicles use this battery without problems in cold crancking throughout the year so the MGA will be no different.
It ha a major advantage over the more specialise batteries that will fit the standard cradle in so much as when it fails a replacement can be bought in any small town anywhere in the world. I had this happen in France last year and simply pulled into a local supermarket and bought a replacement. Had I had fitted the more specialised version then my holiday would have been put on hold perhaps for a day or 2!

For the cable I went to a welding supplier and bought some heavy duty multi strand welding cable and fitted this. The volt drop across this cable will be far lower than the cheap battery cable most suppliers sell to us and well worth the investment for cars with the battery mounted a good distance from the starter motor.
Robert (Bob) Midget Turbo

Graham,here is the site, Vin
ps look at fiat listing
Vin Rafter

"If the original 6 volt batteries had a CCA of 300 does it mean that combined thay gave 600 CCA - potentially a lot of power to draw on?"

No, still 300 CCA. When you put batteries in series, the amps do not increase, just the voltage.

Jeff Schultz

Graham,here is the site, Vin
Vin Rafter

Thanks, Graham
Graham M V

This thread was discussed between 18/12/2009 and 19/12/2009

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