2.5na weird electrical issue

Hiya, can anybody suggest a solution,

I have an ex-military 90 with a 2.5na engine, it has been amazingly reliable but just recently has very, very occasionaly started with a weird starting issue.

When I try to start it, can be warm or cold the lights will show on the dashboard but it will not even attempt to start. Its as if there is not enough power from the battery (its a new battery 6months old). I have a cut off switch/screw on the possitive lead If I unscrew this and screw it back on then it fires up perfectly.

Is it possible that the screw is not making a good contact? can this have this sort of effect.

Any help or suggestion appreciated.

Regards

It could be any of knackered battery, knackered alternator, knackered starter, bad positive cable or bad earth cable.

Although if disturbing the battery is all that takes it to get going with the right amount of omph. I'd be suspecting the cables (which is great because they are the cheapest to replace).

You may have a bad positive or bad earth. Even though the cables look ok, they may have a broken connection, which would usually be right where the cable attaches to its end terminal.

A bad battery or alternator can be ruled out by a quick voltage test when the engine is both running and not running.

Loose connection on starter

Whats rating is the Cut off switch?? it needs to be quite highly rated I wouldn't use anything below 200A @12v switch and if a winch is fitted 400A Its unlikley that your drawing serious amps continiously but you would be surprised how much current a good diesel engine will draw starting especially initial current. Check Earth leads, connections.

If they are loose it will affect starting. Earth leads are a fav on older motors as you could try jumping the cut out switch by this I don't mean putting a jumper wire across it ~I mean move one terminal onto the other so its perm connected. if this cures the problem then the switch is at fault and needs replacing. I have burnt out 2 cheap 150A continious ones winching so now have a marine type 400A at 12v switch.

The Fia ones are only usually 100A continious.

And redhand has a good one check the red while wire to the starter make sure its on the terminal and that the main positive wire is tight.