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Posted by David Sherman on Thursday, March 26, 2009 at 23:28:36 :
In Reply to: 1962 W100 won't start?? posted by rennocs on Thursday, March 26, 2009 at 20:52:22 :
The battery/starter motor circuit is about the simplest circuit in the world, but the currents are heavy. There aren't many things that can be bad -- batter, cables, and starter are the only choices. A voltmeter is your friend. Check the voltage at the actual battery posts while somebody cranks it. If it drops below 8, assuming it's a 12 volt system, charge or replace your battery. If the voltage stays high, check the voltage between the starter + post and its case while cranking. If it's more than about 2 volts below what you measured at the battery, you have bad connections or a cable. To find bad connections, check between one side of the connection (battery post, starter post, or engine block) and the cable itself right where it goes into its terminal. Anything close to 1 volt or more across a cable end and terminal is a bad connection. Without a voltmeter, you can do this last test by cranking for a good while and then feeling each connection to see if one of them is clearly hotter than the others. If so, take it apart, clean it, replace it, or whatever.
Basically, you have two options with any electrical problem -- get a voltmeter and trace through it logically, or randomly replace and clean various things until it works.
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