Voltage sag on warm start

[KK911C4]

Hi,

 

before I change Y cable from alt to starter to pos , I just would like some advice. My voltmeter on car and dash lights go out with a warm start, after 12 miles driving, turn off car, restart is almost nonexistant-- if I keep key to start position, it will eventually turn over.. or I jump car. Battery and alternator are new, starter is Bosch OEM and 2 years old.  I don't know how to do voltage drop test under a load especially as it pertains to checking that Y cable, but everything I've read in the forum points to cable being issue. Car is 20 years old, and cable is original. Is it reasonable to just change that cable? Thanks.

[Ronnie38]

1 hour ago, KK911C4 said:

Hi,

 

before I change Y cable from alt to starter to pos , I just would like some advice. My voltmeter on car and dash lights go out with a warm start, after 12 miles driving, turn off car, restart is almost nonexistant-- if I keep key to start position, it will eventually turn over.. or I jump car. Battery and alternator are new, starter is Bosch OEM and 2 years old.  I don't know how to do voltage drop test under a load especially as it pertains to checking that Y cable, but everything I've read in the forum points to cable being issue. Car is 20 years old, and cable is original. Is it reasonable to just change that cable? Thanks.

first when engine is hot measure the voltage on the battery post in the engine bay, then the alternator battery post the difference of the readings is the loss across the Y, or if nimble positive lead to the alternator and negative to the battery post this will be the drop. This will be the maximum the battery will charge to, remember 13.8 is a fully charged lead acid battery.

[KK911C4]

OK. So one lead of my multimeter to battery post in car, then the other to that nut on air box that serves as ground.. correct? But how do I get to alternator battery post on backside of alt without taking alternator out to get one lead of multimeter on it and the other on the ground? I'm sorry for being dense about it and appreciate the help.

Thanks so much.