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I am dealing with someone that has a 6 volt car, I am trying to set up a set of lights for him, but just got some news that is kind of worrisome, while running and revved to 1500rpm, his battery is reading 7.6 volts at the posts, he also is getting a 7.4v reading at the tail light when the park light is active. Should this be concerning? Does it imply that he may have a bad regulator? I thought that 6v cars were only supposed to put out 6.9v(2.3v per cell). I don't want to sell him a pricey set of tail lights if they are gonna pop at any moment when his regulator completely quits. Thanks for any info that can be offered.
Chip

You will be fine. Look at the charging rate on a 12 volt system. The charge rate of 14.5 volts is acceptable. 14-14.5 volts for the 12 volt compared to 7-7.2 volts for the 6 volt system. 7.2 x 2 is 14.4. You are only seeing .4 volts more than that on the 6 volt system.

The no-load voltage (unlike alternator-equipped cars, the engine may be run with the battery disconnected) for a 6V system is 7.4-8.1V...for the large-diameter 6V generator with remote regulator it's 7.3-8.0V. With the battery in the circuit and loaded (headlights/wipers on) you should see 6.4-7.3V while charging - again .1V less for the "big" 6V generator.
7.6V at 1500RPM with minimal load isn't cause for alarm, it's normal for battery voltage to be 2.5-2.7V per cell when charging and "6V" lamps are able to handle it.

On 12V cars I'll use an 18V cordless battery to test some things, inc. lamps... I've never seen ill effects.

Great info! thanks gents!