Kind of like greased pigs and eels, it is hard to chase down electrical problems. We all tend to try and think our way through it. This is why I am so good at electrical. I don’t over think anything. I just tend to deal with whatever I have in front of me as it comes.
If you are having starting problems or voltage gauge problems or dim light problems, the alternator is often looked at first. Figuring out if your alternator is in good shape can make a guy go crazy. (No, I’m not alternator-crazy, I was born this way. Well, maybe the shock box in school didn’t help). The thing about alternators in Jeeps is that most of the time they do their job right up until they don’t do any job anymore. I don’t worry too much about changes in what the voltage gauge shows or if it cranks harder one day than that before it.
So, when the alternator in Jp magazine’s ’98 Cherokee project started making noises, I told them not to worry about it. When it flat-out died one day, I told ’em it was time for an upgrade. Like any true Jeep guys, they agreed it was time to upgrade and left it in my hands.
I’ve used Mean Green starters and alternators in the past and have never been let down, so I got a hold of a 200-amp unit for the ’98 Cherokee and installed it, shooting pictures of some alternator-diagnosing tech and a few side-by-side comparisons so you could see why the Mean Green was worth the extra coin.
If you see this voltage at the battery with the Jeep running, you know your alternator is dead. Also, you know you have a remarkable battery. It usually doesn’t take much time to dip into the 11-volt range running off the battery. On OBD2 Jeeps as soon as the voltage dips too low, a “check gauges” light comes on in the instrument cluster just in case you aren’t a gauge reader. In pre-’96 Jeeps the gauges are known to be somewhat less than accurate. Keep an eye on what “normal” is for your Jeep and if it drops a couple of volts then worry. Many times, these dirt-choked Jeep alternators start making noise before they die so you should have some warning.
The Mean Green alternators have many awesome features but two huge ones for Jeepers. The bearings on both ends of the shaft are sealed which can help keep dirt and water from getting in and ruining them. They can put out as much amperage at idle as the best factory alternator can. The factory alternator is good for about 30 amps at idle and the better ones can do about 90 amps at highway speeds. The Mean Green alternators can put out 90 amps at idle and are capable of providing up to 200 amps at speed.
The secret of how they do it is pretty simple when you have the factory alternator next to the Mean Green one. The nasty black alternator is the dead one. The shiny one is the new one (just in case you were confused). The smaller pulley of the Mean Green alternator (in the above picture) makes it spin faster. That helps the idle amperage rating. In this picture you can see the larger case, which indicates more windings. More windings always mean more power. To fit this alternator in the Cherokee I had to trim about �-inch off the bracket, but for the Wrangler guys this alternator is a bolt-on.
A tweaker can be a drug addict, but it can also refer to someone who can’t let things go. Electrical guys are usually some form of a tweaker. If you ask five electrical guys what your voltage should be when the Jeep is running you will get five different answers, and they would all argue their point. I can’t let things go, but I have found that the “right” answer for your Jeep is almost always different than the “right” answer for your friend’s Jeep. This tester has the green range from 13.6 volts to 15 volts. I have other gauges that say 13 volts to 14.5 volts is ok. I’ve had batteries not start at 13 volts and I’ve overcharged batteries at 15 volts. My rule of thumb is that anywhere from 13.5-14.5 volts will let you get back home if your battery is in good shape. A half a volt less or more than that is still okay, but you should keep your eyes on it.
