It's amazing what you can do with simple test equipment. Volt meters are great but they can trick you into thinking something is OK when its really bad.
I've fixed things faster with a test light and usually doesn't need batteries.
Take for example, checking grounds. Just how do you check a ground connection? Ohms reading? The few microamps a volt meter might pass though a connection will look like a great connection but a test light will pull a few more amps and a poor ground will show up as a dim light. Of course you would be more accurate by using the voltage across the ground connection when under load but who thinks of that and who has time to hook up a load right away anyway.
I've made a 10' extension for my test light so I can make one connection right to the battery and i am able to all the way to the back of my CJ.
Connect the test light to the (+) post to check the ground circuit path.
Connect the test light to the (-) post to check the 'power' circuit path.
Always check the test light first to make sure it is actually working.
Test lights are a great way of checking fuses rather than looking at a fuse.
Will also act as a short indicator when a test light is inserted in place of a fuse that is always blowing.
When connected between your battery and battery cable will act as a leak indicator in case something is still drawing current and killing your battery when your jeep is off.
Also use it as a trouble light to see what you are working on in the dark.
Heck, I've used a test light to run my alternator when the regulator died on my 70 CJ. I connected the light between the battery and the field to keep the alternator charging to get home one night. Just had to be careful not to pump too much voltage into the wiring.
Spend the $6.00 for a test light at W-mart and throw it in your glove box.
I'ts like carrying a towel when hitch hiking.
Maybe JH will make up a CJ Test kit that will include a Test light, 10' extension leads and a instruction manual for around $15.00 to sell.