Accepted Answer

Hello Jay and thanks for using JA, the problem with your mustang, is not really a problem with the actual car itself, but with the added components. The charging system is controlled by the PCM, and is designed so that the PCM will decide how much alternator output is needed and when it is needed, the most important thing the PCM does is to keep a constant supply of 12 volts to all the modules so that all the electronic systems in the car are fully supplied with the power they arfe designed to work off of. When you add aftermarket components that will draw some of this power away, the PCM will notice the extra demand and adjust the alternator output, but in your case the output requires the alternator to charge at 15 volts instead if the usual 14.2-14.5 and in turn is creating a scenario that the PCM does not like and therefore sets the warning lamp on. The charging system is designed to handle the factory installed components, however major additions can overwork the system and cause this to happen. I know that is not the answer you wanted to hear, but unfortunately it is the one that is correct. At the dealer we see all kinds of strange problems with the newer cars due to add ons and we usually suggest having the wiring done by us, as it turns out that the aftermarket installers don't take the time to properly find the wiresw they can use, but just tap into the closest, most convenient one that has power or ground, whichever they need, and with the PCM controlled charging systems, you can't do that. There are places in the fuse box that can be used for the proper installation of these components, and when installed properly, will allow all systems to work properly.

Expert:	davehop
Pos. Feedback:	99.4 %
Accepts:
Answered:	2/24/2009

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