ign lite on when idling

[wellskint]

my 1500 thats not yet back on the road but hopefully will be soon, when idling the red ign lite stays on. what causes this please?

[yorkshire_spam]

my 1500 thats not yet back on the road but hopefully will be soon, when idling the red ign lite stays on. what causes this please?

Low tick over or a slack fan belt? Roughly what RPM do you have at idle?
It could be the early signs of the rectifier diodes failing, but I'd start with the 0 cost options of idle speed and belt tightness.

[xvivalve]

^ what he said

[maitretjak]

Or, like I once had on a sprint, a faulty connector to the alternator.

[Aleco]

Another vote for the connector to the alternator. Oddly enough I had the same symptoms with the addition of the light occasionally flickering at high revs.
I replaced mine with new one from AES spares.

[Richard the old one]

Another vote for the alternator connector. I obtained one from Moss as they have a branch in Bristol. It was a stock item.

[Aleco]

Word of advice though, unless I made heavy weather of it, it's a simple if fiddly and awkward job to do.
The cables going to the original connector were to short to cut and attach new female connectors to. I had to make short extension cables and solder them to the original ones.
Not difficult but a pain in the backside when leaning over the wings and soldering in the bowels of engine bay.
Oh and don't forget to disconnect/take out the battery!
I clearly had a bad day and got totally focussed on the cables. I remembered about the battery as one of the cables sparked against the engine block

[Graham04]

Have you put a meter on the battery when the car is ticking over and at 2000 rpm. With a decent battery you should have around 12.8v on tick over and about 14v at 2000 rpm. Try this without and with a load (lights, fan, heated rear window and wipers on). It will give you an indication of the alternator output. The voltmeter in my car reads almost half a volt too high but is still a useful indication.