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Posted by David Sherman on Wednesday, March 18, 2009 at 12:07:59 :
In Reply to: Re: Do the brake lights go on? posted by Dave Horvath on Wednesday, March 18, 2009 at 08:05:36 :
Since you have other electrical problems too, the brake light problem is a side issue. I'm sure I could figure it out pretty quickly if I was there with a voltmeter, but I'm not sure how to talk you through it. If the cranking is slow, that might be the place to start since that's the simplest circuit, and the one that draws the most current. Make sure you have a good battery, well charged on a battery charger and try cranking. If it's still slow, have somebody crank it while you check the voltage drops from the battery posts to the chassis and to the starter motor. More than 1 volt or so of drop while cranking, across any connection is a bad connection. If you find, say, that there's a big drop between the grounded battery post and the chassis, then check each end of that wire (post to cable, and then cable to chassis) to see where the big drop is. That will be your bad connection. Check also the voltage right at the battery (between its posts, not between its cables) while cranking. A 12 volt battery shouldn't drop below 8 volts or so, and a 6 volt below about 4.
Beyond that, there are too many things to speculate about. The key to electrical troubleshooting is divide the system into small chunks and isolate the problem. Start with a known-good, well-charged battery and do your tests just on battery power.
Once you know the wiring and battery are good, then start the truck and see what's going on with the regulator. Charging voltage should be in the range of 14-15 volts or 7-7.5 volts. If it's too low, briefly jumper the field to the hot battery post and see if the charging voltage jumps up. If it doesn't, suspect the generator. If it does, suspect the regulator. If the voltage is consistently too high, and you know the battery is good, the problem has to be the regulator (a totally shot battery can present so little of a load that even a good regulator will send excessive voltage to it). You may possibly have ruined the optima battery by overcharging it since sealed batteries can't handle overcharging like traditional ones can.