testing the ignition coil

[Tripp]

so i have my 5.0L in my ranger and i can crank it over and have fuel pressure. but i'm not getting spark. i've followed this worksheet to diagnose the no spark: http://www.therangerstation.com/tech..._worksheet.jpg
but everything checks out good. my question is when testing the ignition coil it says to put a test light on the negative side (which i get 12v on) and crank it over and it should pulse the light. it does that for me but its a weak pulse and with the multimeter it shows it dropping from 12v down to 8v-9v and fluctuating around there. so i'm guessing thats good. but it does the same thing when i put the test light on the positive side. should the positive on the ignition coil be a constant 12v or should it fluctuate during cranking like the neg side?

 

[sparky2eh]

Well in theory it should be a constant 12 volts at the positive terminal, as the voltage "hasn't been used yet". The negative side should fluctuate as the engine turns over, your meter probably isn't fast enough to show the fluctuations to 0 and back.
Do not try and measure the centre post voltage, ie the wire to the distributor bad things can happen as that is a lot of voltage.
My two cents

 

[kimcrwbr1]

The best way to check the coil is put a plug in the coil wire from the dizzy and set it on a good ground then turn the key on and take a jumper wire from the neg side of the coil and just touch it quickly to ground the plug should fire pretty blue if not it could be a bad ground to the coil or the coil itself. dont hold it to ground just quick touches.