My dads got me to sign him up on here and post this so I apologise if my terminology isn't quite right.
He's an ex-miner and still has some bits and bobs of equipment lying around and is also acquiring some parts from ebay and the likes to keep his memories alive and a nice set of collectables.
He is currently struggling to recreate a charger as they used to have in the pit/
The lamp head fits correctly onto the adapter he bought / mounted and has power to this
He also has an Oldham D.C. Amperes meter which needs connecting up but can't remember which way it goes.
As far as I am aware, an Ammeter as it basically is, goes in series, so I am guessing this would put it in the live leg from the PSU that is feeding the mount, please correct me if I'm wrong on this.
With that in mind though, is he right to state that the negative leg should be to the 'peg' that goes inside the lamp, with the positive(+5v) being connected the outer case of the cap lamp.
Any help would be appreciated as he's struggling and doesn't really want to damage anything.
A second question as well, what Amps rating should his supply have. There will only be one battery pack connected at a time

Right on first and wrong on the second.
Yes ammeter goes in series, usually provides resistance enough to control current but dont take this for granted as I dont know your setup.
Old computer power supply will have a 5V outlet by the way, but dont get mixed up with the 12V what ever you do.

The correct charging voltage is 5V for Oldham lead acid.

The little dome on the bottom of the headset is the positive contact, so the spring it contacts is +V, the keyway is -V.

Pity you not local, I haves lots ammeters and charging clips.

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http://www.ebay.co.uk/itm/OLDHAM-CHARGER-FOR-CAVING-POTHOLING-LAMP-TYPE-1-/161195658005?pt=UK_Sporting_Goods_Climbing_Mountaineering&hash=item2588028b15 

They pop up on eBay from time to time. Not the exact same model, this is newer and a single unit rather than a rack charger, but the same output.

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Thanks for the quick replies.

Least it's connected the right way. His other question was the Amps. Is there a minimum the transformer should be giving, it's definitely giving him 5v, but concerned he might only have a 500mA limit on it?

A pc psu is an option as I can acquire one for him through work for the right price but, excuse the dumb question but can that have too many amps coming from it?

The safe max is 1 amp on a flat battery which will drop to a trickle when the battery is fully charged.
Now I dont want to rain on your parade but this is the outdated way of doing things. Remember when you had to top car batteries up?
That was because they never actually stopped charging, and even a trickle into a battery thats already fully charged will cause some gassing and loss of electrolyte.
The last lead acid battery chargers produced were electronic and would cease charging completely when the battery was fully charged.

I know the old ammeter job was the traditional charger your dad was used to, but we move forward.

I have a quantity of genuine Clarke manufactured for Oldham charger PCBs, they are actually the well known tool people.

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