I am trying to track down a problem in a car. A fuse keeps blowing. It is my understanding one way to do this is to remove the fuse and place a test buzzer/light in the connections in the fuse spot. With all circuits closed, I should have no power going through this fuse location. If I have power there is a short is this correct? I understand power is coming from the battery to one side of the fuse, but unless there is a "ground" there should be no power going through it correct? How does that work exactly. Please keep it as simple as possible. Thanks in advance.
You have described it pretty well. But you need some clarification...
A short is a premature copper to copper connection... IE two wires have rubbed through thier insulation and are making contact.
A ground fault is were a wire is comming into contact with the frame of the vehicle or other non wire related component completing the circuit.
You are correct in thinking that you can put a low wattage light, buzzer etc. in the fuse holder to see if power is flowing with everything off.
NOTE! Do not use the buzzer if there are electronic components run off of this fuse. If you accidentally leave one turned on, the buzzer can set up voltage spikes that can cause damage to the electronics, beeter to use a low wattage light.
First ensure everything that you know of in the circuit is turned off (Open circuit).
Remove fuse, insert test unit (light).
If light comes on, it indicates that power is still flowing in the circuit. This can be caused by;
Short - wire to wire prolem Failed switch Ground fault - wire to ground problem Something still live in circuit (dash clock / radio etc.)
If light does not come on (make sure you are using a low wattage lamp), but fuses are still blowing, it indicates a low resistance problem after the switch, or a resistance problem at the fuse holder.
It is a common problem for fuses to blow after a period of time due to heat build up at / near the fuse holder (corrosion of connector to fuse block etc.), common problem on high amperage circuits like lights / AC/ Heater circuits.
If light comes on, and you KNOW there are no other items in the circuit that may be using power. Go to final component in circuit, IE heater motor, and disconnect. Did the light go out?
If so, you know that the component is the probable source of the problem (IE shorted windings in heater motor).
If light stays on, you know the problem is before that component, follow harness back to next component, disconnect ground side of component, does light go out?
If so, harness between component one and component two is culprit.
If light is still on, disconnect power side connection of component two. If light goes out component two is source of problem.
If light is still on continue as descried above until you have found point that light goes out. The component directly ahead of that connectin has something wrong with it... Either a short or ground condition.
Was a Heavy Duty Mechanic for about 20 years, before changed carreers. The above system works as long as you go step by step. If you try jumping ahead you may screw yourself up, and change the wrong parts..
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