ok, for all those of you that have slow cranking starters, first you need a decent preferably digital voltmeter, you also need a charged battery, if the battery doesnt show at least 12.2 volts then charge the battery, a full charge is 12.8 volts.
starters often crank slowly because there are bad connections between the battery and starter or engine earth, checking is very simple.
like the pic take your voltmeter put one lead on the battery terminal itself, the other onto the stud on the starter where the main battery cable goes, then get an assistant to crank the engine, although both leads of the volt meter are on the positive you will see a voltage reading, that reading is the different between the battery and voltage reaching the starter, anything more than 0.5 volt indicates a bad connection, or maybe cables which are too thin.
you can do the same with the earth side of the circuit, hold one lead directly on the battery terminal and the other onto the starter body, again crank the engine, you should see no more than 0.5 volt, as above if you have more than 0.5 volt you have bad connections or cables that are too thin
infact you can volt drop between any two points of a positive or earth circuit to narrow down where the fault actually lays
90% of cars which crank slowly but have a healthy battery are suffering from bad connections that could be found with this simple tests hopefully this will help some of you
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