by dave-r » 22 Mar 2001 8:49 GROUNDING
The importance of a good chassis ground, on all electrical components in your car, cannot be stressed enough. A bad connection to ground will act either as a switch and cut power to the circuit or it will act like a resistor and drop the voltage going to that component. A drop in voltage means a corresponding rise in current, therefore heat, in the circuit.
In the lighting circuit, bad grounds can cause funny things to happen. How often have you followed a car and seen the tail or brake lights going dim, or even off altogether, when the indicator flashes or brakes applied?
The most important connection though is the engine ground. A bad ground on the engine can make a car difficult to start and can drop the voltage to the ignition system.
The ground side of the battery can be connected in two ways:
1) Directly to the engine and then a separate lead from the engine to the frame.
2) Directly to the vehicle frame and then from the frame to the engine.
Both can be accomplished using as few as three connections. If possible, the first method is preferred over the second.
Surface preparation for grounding is important. Don't depend on the screw threads to do all the work. Make sure there is bare metal under the connectors and, if possible, use a star washer which will "bite" into the metal and make a good connection.
A quick test on engine ground can be made with a voltmeter. You will need a meter set to a scale that will read D.C. volts from 0 up to 2 or 3 volts.
Remove the coil H.T. lead (to prevent engine starting). Put the negative probe of the meter onto the battery negative (negative earth cars) and the positive probe onto a good solid ground on the starter motor case. Have a friend crank the engine and check the reading on the meter.
If there is more than 3/4 volt drop from the starter case to the negative battery terminal while cranking you should carefully inspect the battery cables, clean up all connections and make sure the bolts holding the starter motor are tight. If you still have over 3/4 volt drop then you can try heavier cables on the battery.