Failed charging system
This 2007 Jeep was displaying the red ignition light on the dash and a quick test with a meter confirmed that the alternator was not charging. The most obvious decision would normally have been to fit a new alternator, assuming this was the failure point.
We have done this in the past, only to find that there was another reason for the battery not charging. Due to this, we always carry out one further test: we check the battery voltage at the alternator terminal.
It may surprise you to know how often we have found that a poor connection or a broken wire is the reason for a failure to charge. Sure enough, on this Jeep we discovered that the voltage showing at the alternator was around 1.3V. This confirmed that another problem was present, so we removed the battery to access the cable between the alternator and starter. It is very common for manufacturers to jump a battery cable from the starter terminal, and if a problem is going to occur, this is a common place.
Once we had access to the cable, we discovered that the terminal had fractured and broken away, leaving only the lightest of contact between the two. Fitting a new terminal to the cable restored contact and the battery was once again charging.