SPQ13 Tracy

Another quarter starting with electrical troubleshooting.  Most of what we've been covering in class has been a review, but has been helpful in many ways.
Things that I will take from this week about electrical troubleshooting:

• Circuits are circular - Any circuit in a truck must have a voltage source, circuit protection, a switch, and a load.  Any break in the circle creates an open circuit.
• Current is the same throughout the system - In a series circuit, the voltage is distributed between loads.  This is very helpful to remember while finding short.
• Troubleshooting starts at the load - Black lead goes to most ground point - battery.  Red lead starts at the load and moves from there.  
• 12V before and after load - open ground side
• 0V at load - open hot side
• <12V before load and 0V ground side of load - voltage drop hot side
• <12V before load and anything other than 0V ground side of load - Voltage drop ground side of 

When I was working on the relay boards today I was noticing a few tricky ones.  The relay operated fine (hear/touch) and the load read 12v before and 0v after.  Tested the voltage drop on both sides of the relay out of curiosity and found that there was less than 12v before the relay and 0v after.  Chased them down to find voltage drop on the hot side.  I am pretty sure I didn't catch this the last time I did the boards.  

Found that the driver headlight was out while the passenger light was still on.  Hooked my black lead to negative battery and probed at the light with red lead.  Read 12.4 (ish) until I tested the ground side.  Took the terminal going to the head light apart and found this.  Obvious open ground side of circuit.

Hours:

Week: 40

Total:40