I have had fluctuating voltage issues come and go usually when it raining or snowing. Had a red wire going to the positive terminal that was loose so fixed that and hadn't had problems for a few months. about a week ago the check engine light came on and my voltage was pegged out. Next day returned to normal. Two days ago when this storm hit i had to use the truck and my voltage went way up then dropped to about 10V according to the gauge then slowley crept to 8. Yesterday, put the battery charger on and after about 4 hours i was able to start it but just barley. put the charger back on today, took it off and the battery is reading about 13V. Turn the key on and it looses all power almost instantly. Sound like the ECM? Been serching the web for hours and dont have a clue what to try and im tired of rolling around in the snowy -degree weather. Anyone got ideas?

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got error code 41- generator field not switching properley. wtf does that mean

 

jeez im in the same boat, i have close to the same issues and i still havnt figured it out yet, but what i did was wire up a external voltage regulator. and i still got some problems it dont regulate properly i got to turn it on and off again cause it overcharges but at least i can charge the batterys up

 

ok got an external voltage regulator to wire up. where is the best place to find a 12V ignition source? hope someone out there will give some sort of an answer

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wired it up jumped it it ran for a couple minutes then shut of without warning. im lost now and dont have a direction to go. This site ain't what it used to be. Guess i will just park it.

 

My serpentine belt shredded and cut the wires on my crank position sensor (located on the front of the engine just above the harmonic balancer). I had replaced my alternator even though I didn't really think that was the problem. It started charging again after I replaced the sensor.

 

what year truck? my 90 w250 did the same thing . I replaced alt then replaced a few grounds then replaced the shutoff solenoid and that cured it.

 

1992 350. A lot of added on stuff under the hood. It's a little motor home that has extra battery added to power interior lights, water pump for plumbing, etc. Former owner added a battery isolator so the alternator would charge extra battery but not let extras drain engine battery. Had some work done and the turkey cut a cable and disconnected the isolator. Don't know how to rewire isolator now.

 

If it was me I would disconnect the second battery and try it see if that cures the fluctuation . If it doesn't I would check out with a amp tester