Stranger12

Hi ,

I am trying to do voltage drop test on my starter and one questions i have is , why do you connect the pin to positive on the battery and positive on the starter to test for voltage drop ?

I have watched youtube videos and read articles on how to do it but what doesn't make sense is, voltage is from positive to negative so how can I see excess voltage coming to the wire when I am only using positive positive or negative negative ?

for instance you do the negative side with black pole on ground or battery negative and the other side on starter body .

or do positive voltage drop test by connecting one pole to the positive of the battery and another to the positive cable or pole of the starter.

I appreciate your help.

thanks

pcy

Are you testing the starter on the bench? OR testing the starter while it's installed on the car?

Stranger12

On the car

BimmerFan52

What you are looking for is a difference in potential between the two points that will be indicated by current flowing through your meter. See below.

How To Perform A Voltage Drop Test - Help With Automotive Circuit Diagnosis

abe76247

Yes, you go positive to positive to check the voltage drop in supply side and chassis to engine to check the voltage drop of the ground cabling. Polarity is not important but if you want to not have a (-) in front of a reading to give you pause then put red lead where vltage is higher and the other where it will be lower. For positive side the red is always towards supply and the black towards the load (starter, light bulb , etc.). For negative side Red towards load and black towards the chassis or battery ground post is the way.

A volt meter reads the difference in voltage between where you have placed your leads. If that is batt - and batt + posts then it read batt voltage. If it is on a cable where while starter is engaged there is 12.03 V and at stater there is 10.23V then you would have 1.80 V on meter. If you find over 0.3 V on the circuit then there is too much drop for most circuits. 0.3V would be the limit for the starter cables. Some circuits that have long runs of wire and are not voltage critical can have higher allowable voltage drop.

If the voltage drop is over 0.3V then you can repeat test at connections to see if there is one connection responsible for most of the voltage drop. One lead on batt post and the other on the cable terminal and then operate starter and you will see if the connection is dirty. The center of stud where batt cable attaches on starter solenoid and the terminal at that connection will tell you if the connection there is not good.

twh

Years ago, I helped a friend debug a Nissan that wouldn't start. All voltages seemed ok at the battery and even at other places. But, when the starter asked for juice, it just wouldn't go. Turned out to be a mostly gone fusible link. The fusible link wasn't completely gone, so the static voltages looked ok. But, the fusible link was gone enough that it wouldn't pass any decent current to get the starter motor to turn. Turned out to be a $10 fix, but it took us an hour of head scratching. Don't know if BMW's use a fusible link or not in any places.

Stranger12

many thanks for the info . I will be doing a test on my car soon