You do not really need a dc clamp ammeter. The voltage from your cigarette lighter would sag substantially if there where a transient system overloading. In fact you cannot monitor for transient situations in service with one.

Even glow plug relays coming back on intermittently will not usually kill the alternator but will lower both the stored charge in the battery and reduce the voltage coming from your cigarette lighter. This is about the only practical way to monitor your system for the next while.