Ignition warning light on

XJ
1

Gents, in last week, my 71 xj6’s ignition warning light stayed on after the engine was started. I searched archived posts in the forum, which suggest possible problems with either the alternator or battery.

I used a multimeter to measure the voltage, with the following numbers under different conditions:

  1. 12.40V, engine off, after car parked for 4 days
  2. 14.01V, engine idling at 850rpm, 14.10V, engine running at 2000rpm
  3. 12.69V, engine off, measured on the next morning
    The battery is about 13 years old, but covered only about 2500 miles. So what is the normal voltage range I should look for at the battery?

Thanks,
Fan

2

Car batteries generally don’t last 13 years. I’d have it tested, or just replace it.

3

Your voltage readings are normal, Fan - though 12,4V after only 4 days is suspicious.
But that a 13 year old battery performs at all is only a bit short of miraculous - it’s time, not distance, that finally kills a battery. After four years of use one is not too surprised if a battery starts showing it’s age…:slight_smile:

But it is not your battery, or alternator, that causes the lit warning lamp. The lamp is connected to the ign key at one end (white wire), and the alternator at the other (brown/black wire). With ign ‘on’ ('12’V) the lamp is grounded (lit), normally through the alternator - with engine running; the alternator voltage ('14’V) counter the battery voltage, and the lamp unlit.

First check tat the brown/black wire is connected to the alternator, not fallen off/grounded…

That said; there is enough juice in the battery for cranking, and for lighting the lamp - and changing the battery won’t fix the fault. But a 13 year old battery has surpassed it’s normal life span…:slight_smile:

Frank
xj6 85 Sov Europe (UK/NZ)
**

4

Thank you Kirbert and Frank. I bought this car about 6 months ago. When I checked the receipts came with the car, I found battery and tyres were both replaced in 2009.
As Frank suggested, I checked the wires, disconnected and reconnected them. None of them were off but all rock hard. The ign light is still on at the moment, I will change the battery first.