Electrical Mystery

Here's a puzzler. My alternator gage is showing discharge at idle...thought it might be the alternator. Local garage said it was "weak"...but not faulty.

Strange things happening. Like, for instance, when in the vehicle (key in ignition, but off), the chime sounds when I push on the break, or when the passenger electric seat controls are used. Also, seatbelt light came on, then off, then back on the other day...and I had the seatbelt fastened at the time!

Any ideas? I know electrical issues can be hard to trace...wondering if anyone else had experienced similar strangeness.

NJot sure about that problem in particular but I would say to check your grounds first of all. Many times if you have a bad ground some freaky stuff can happen. Good luck

Yup, grounds, start checking them and clean them as you go. Start at the front bumper and work to the rear. Grounds can do some strange things. If a certain 'item' cannot find a ground/return it will use something else or some other path which causes the freaky stuff.

Yup, sounds like grounding problem.

I suspect there is a chassis control computer somewhere that controls stuff like you mentioned. Many logic circuits like the ones in that control use TTL type chips. These chips output a logic level "0" (zero) which is zero volts or logic level "1" which is 5 volts. If there is a problem with ground, power, or the computer these logic outputs could "float" somewhere between 0 and 5 volts. Say one of these logic outputs controls the seatbelt light, as the voltage floats up and down randomly the computer turns the light on and off making its best guess whether the floating logic level is closer to 0 volts or 5 volts.
Start by checking the chassis ground.
Good luck

Chuck

FlyFisher --

It would help to know what year XJ you have. The early ones use a Delco alternator with an on-board voltage regulator. The new XJs use the PCM to regulate the alternator output.

I have to go with Fanatc and Rich, grounds can do some crazy crap, witnessed that first hand, check em all, there should be one up on the radiator core support, the main batt ground, one from the block to the firewall and at least one more under the dash, did I miss any guys ????

I had the same thing happen this morning with my seatbelt light in my 1990 Limited. It came on and went off again several times and I realized it was occuring as I hit pavement cracks and other bumps. The rain overnight and this morning was very heavy, possibly creating a part of the problem.

Would this likely indicate a ground issue or would you start with looking at the switch in the seatbelt latch? It's my understanding there is a simple switch in there to indicate that the belt has placed.

The rig has 231k miles on it and has seen it's fair share of seatbelt use. And since one is used everytime it's moved, do you guys see any reason to not disconnect the switch and/or pull the light bulb out if the problem continues?

I would go with grounds as the likeliest explanation. It doesn't hurt to add a couple of new ones either. You should also know that the built-in voltmeter is a terrible liar, especially on the older ones. Various accessories, including the heater fan, will show an alarming drop, but this is only because the wiring to the voltmeter is inadequate, not because the charge rate is bad. When in doubt, always check the voltage at the battery.