voltage fluctuations

I have some voltage fluctuations that acts like this:
When driving in the dark and switching from hi to lo beam or low to hi the voltage starts to vary from 14 to 13 approximately and the lights varies accordingly. It varies with a frequency of 3-4 per second. And it lasts for a few seconds then it gets stable at around 14 V. It also does this when I hit the brakes (brake lights) or put the heater fan on full blow. WHen power consumption changes it starts to vary. It does not do it all the time. I first noticed it last year. The alternator was changed last year. The voltages are approximate only read from the meter in the dash.

it is a 89 cherokee 4.0 automatic.

Torfinn

Start off by checking your grounds - especially the one from the engine to the firewall. A "floating ground" is a common cause for voltage fluctuations - the Delco alternator that AMC spec'd for the XJ is quite a reliable unit.

Also, make sure the main engine ground is clean (passenger side of the engine, above the starter) and that the alternator mounting bracket is clean (no oil leaking onto it.)

When you check and clean a ground to painted metal, take a wire wheel in a drill motor and clean a small patch (about the size of a postage stamp) down to bare metal. Centre the patch on the screw hole holding the ground. Coat with corrosion inhibitor (I prefer Gardner-Bender Ox-Gard) on reassembly.

If the engine-firewall ground strap is visibly dirty, you'll want to replace it. Many RENIX (1984-1990 XJ w/AMC engine) electrical problems can be traced to a faulty or dirty engine ground strap - it's called "The RENIX Killer" for a reason!

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