1st Gear Member
Join Date: May 2004
Location: Rhode Island,USA
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It's very unusual to have the voltage drop as you describe. The only thing that makes sense is that as some wire heats up it's resistance increases as it expands and as a result the voltage drops until the car dies. First, take off both battery terminals and clean them just to make sure that they are ok. Next, look at the ground wire.( It's unlikely that the new voltage regulator is also bad. )
It connects to the engine on the passenger side by the strut tower at the rear of the engine. Unbolt it and clean the connetion and terminal. If you still have the problem, take a jumper cable and connect one end to the negative battery terminal and the other to the engine block if it will reach. (Leave the ground wire on the battery)If it's not long enough, clamp it to the chassis under the car. ( THis is to check that the ground wire itself is ok.) If this corrects the problem, the ground wire needs to be replaced.
Also, if it was me, I would temporarily replace the battery with a known good one from another car BEFORE I did anything else. I know that you had it load tested, but batteries are strange birds. They can act in bizzare ways. I've spent a lot of time and money troubleshooting problems that ended up being the battery.
If you still have the problem, I'll go throught the next steps n troubleshooting.