Positive or negative ground - CLK-Class Mercedes-Benz Cars & Trucks

Depends if it is positive or negative earth.
If negative earth, the positive post. If positive earth, negative post.

In modern automobiles' 12V systems the positive is an isolated system and the negative uses the vehicle's chassis as the conductor. Since DC voltage is a two wire system there is no such thing as a ground per se. Any grounding that would be required would be referencing the negative terminal anyway. So you could ground anywhere there is bare metal in the car.

ALL modern cars are positive ground. What did you do?

Disconnect the ignition coil output wire at the distributor cap.
Connect a spark plug to the end of the ignition coil output wire which you just disconnected.
Connect a ground wire to the threaded portion of the spark plug.
Disconnect the ignition coil ground wire from the negative terminal on the coil (Green Wire).
Connect one end of a ground wire to the ignition coil negative terminal.
Turn the ignition switch to the ON position.
Tap the other end of the ignition coil ground wire jumper on an good grounding point (for example the battery negative terminal) and look for sparks at the spark plug that correspond to the frequency of your tapping of the ground wire.
If you have a good spark at the spark plug, the ignition coil is good.
If you don't get a good spark, check for approximately 12 VDC from the coil positive terminal (black wire) to ground with the ignition switch in the ON position. You should also get approximately 12 VDC from the coil negative terminal (Green wire) to ground
Ignition Coil Resistance Check

In addition to the test above, you may elect to perform an ignition coil resistance check as confirmation of the coil's condition.

Check the ignition coil primary coil resistance by connecting an ohmmeter between the positive (Black wire) and negative (Green wire) terminals on the coil. The resistance should be 0.4 to 0.6 ohms.
Check the ignition coil secondary coil resistance by connecting an ohmmeter between the coil output terminal and the ignition coil negative terminal. The resistance should be 5000 to 7200 ohms.

You may have a bad coil or bad ground or wire connection

If you have a multimeter, it should be easy. Black lead on frame and red lead on "hot". If you read -12 Volts, you have a positive ground. If you read + 12Volts, you have negative ground system.

If you are running a 24 volt starter with two 12 volt batteries
Battery one negative to ground on the vehicle. positive to negative post on battery two and positive on two to the starter.

Is a 2002 Volkswagen beetle positive or negative ground

first you need to check your unit maybe it is grounded,,how to know if your unit is grounded? using tester get your tester in x1 mode, test the tip of battery terminal positive to positive negative to negative, automatically the tester make a deflection.after that switch it .. positive battery terminal to negative wich is the color black wire of the tester,if theres a deflection again ,,,, your unit is grounded

Are you sure you were touching the negative post and not the positive post. If you checked the positive post and the other wire to body chassis then you should get the reading you say here. Negative to negative is negative and you should have had no reading at all. Please do this test again being absolutly posative your touching the negative post. There will be a - sign on the battery under that post. Get back to me after the double check, Raz

Hi
It is definitely negative ground mate.

Cheers

Jason