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Posted by Sherman in Idaho [72.47.9.37] on Thursday, November 29, 2012 at 11:42:26 :
In Reply to: idiot light posted by Jerry in Idaho [69.59.83.175] on Thursday, November 29, 2012 at 01:06:52 :
First look, then wiggle. Once you've done that, rather than shotgunning it (disassembling, scraping and reassembly each one in the hopes of hitting the bad one), get a digital voltmeter (cheap $3.99 one from China will do, since accuracy doesn't matter), set it to the lowest range (usually 200 mV full scale), and check ACROSS each terminal with the engine running. For example, to check the battery connection, you'd poke one lead into the battery post, and poke the other into the cable clamp. Then poke one into the cable clamp and the other into the wire going to the cable clamp. On a crimp-type terminal, poke one lead onto the screw and the other into the wire going into the crimp. If the insulation is old and hard, or cold or thick, it helps to sharpen the lead to a needle point, or poke an actual needle through the insulation by holding it with pliers, and then touch the test lead to that. There should only be a few millivolts of voltage drop across any connection in a functioning electrical system. You'll soon find out what's normal, and then you'll find one that is very much higher (at least hundreds of millivolts, and possibly even more than a volt) than the rest. At that point, you'll know which connection needs fixing and you won't have wasted time re-doing everything and wondering whether you've finally got it this time. It's also possible that the act of poking will make a bad connection temporarily good, so have someone watch that idiot light and tell you if it goes out when you're checking. In this case, it will be the field lead and all regulator leads that you'll be checking. Battery cables and battery ground are undoubtedly okay since the truck cranks fine and that draws way more current than is needed while running.