I have 1996 jeep cherokee with 4.0l high output. driving down the road and my check eninge light came on than my gen light. So i checked voltage at 12.5 ok so i got a alternator put it in same problem put 4 guage wire from alt to batt same problem. Now im going damn so i think maybe not enough ground put 4 guage from batt to motor. no fix yet. so i find out the only time the voltage freaks out is when i have the fan switch on. u can have the a/c system on but if the blower isn't going voltage fine but once that fan motor is on voltage drop out to 12.5. cleaned the ecm and played with it a little dosen't seem to be the problem. Is there some way the blower fan and alternator see each other? turn headlights on no voltage drop stereo same thing only with the fan motor from what i can see. Im using a power probe 3 to watch voltage not dash guage. Any idea's would really help.

 

"fan switch"? Are you talking about the HVAC blower, or did you add a manual switch to the radiator fan?

 

Talking hvac switch.

 

Sometimes those blower assemblies pull enough current to melt the connector above the passenger's footwell. Might take a look and see if anything's wrong.

 

Foot well are u talking under pss side inside dash or under hood?

 

Under the dash on the passenger side.

 

ok looked under dash found no plugs in trouble. But i unplugged the blower and resistor for the blower and turned on the truck no voltage drop im thinking its a bad resistor some how it is doing it. No clue how it would have any thing to do with charging since its not the pcm. What i was thinking about doing is wiring in a 12 gauge line to the switch from the battery and back out to the blower and just have one speed full on. It would by pass this hole problem that im not really sure what the problem is yet. At this point this is what i know for sure. When i have the truck running and blower fan off 13.7 at battery and signal coming in to the alternator to make it run. the second i turn on the fan signal gone at alternator and 12.5. Now if i rav it to 3k and hold it the signal will come back after like 2 mins.