Ballast resistor

[Dave WM]

Sometimes my car seems to start best if you turn the start key to start, then release to run, that's when it begins igniting and running on its own.

I was thinking about this and wondered if its possible I had an intermittent key switch issue.

I get my analog meter (better for quick changes in current flow readings) and hook up to the + side of the distributor connector on the ballast resistor (the spade connector). I disable the starter solenoid (pull the spade connector) and check for voltage in the run position, looks good, then I advance the key to the start position, still voltage but a drop, him that seems odd, I review the FSM and confirm if anything there should be less resistance in the circuit so voltage should be higher with Key in Start. I then review the color code, my Blue (BL) wire is on the outside (highest resistance to coil) side of the ballast. The black white (BW) is next. If I read this right the run position is always getting the lower resistance (higher voltage) that should be used for starting and the starting is getting the higher resistance, lower voltage to the coil for start.

the wiring looks pretty original.

 

[Dave WM]

never mind I was reading it completely wrong. there is a black and blue on the end, and a black and white next, I was reading from the wrong end, did not realize the BL was Black and Blue while L is blue.

[SteveJ]

What year Z, and where did you get the wiring diagram you were looking at? From that I can give you a better detailed description of what should be going on.

[Dave WM]

75 280z. FSM electrical section.

I will be testing again later now that I can read the wire code better.

my test will be do check voltage at the positive lead of the coil while turning the key to ON and then to START with the starter disabled by pulling the solenoid lead.

I presume I should see a higher battery voltage at the coil when in the "START" position vs the "RUN". esp since the starter motor is disabled so no starter load on the battery.

Edited March 28, 2017 by Dave WM

[Dave WM]

forgot about the load of the fuel pump in the "START" which tends to reduce the overall voltage during the test. When I tested again as described above the voltage at the coil  was about the same maybe a little bit less in "START" again I presume due to the load of the pump.

[SteveJ]

The starter motor is a very sizable load. It will draw a lot of current and pull down your voltage, especially with an older/weaker battery. The fuel pump is nothing compared to the starter.  Post the voltages you are measuring, starting with the battery and the car off.