So a few days ago the Samurai refused to start. After checking the ignition coil, I found that the resistance across the primary coil is off by a factor of 4 or so (mind you the multimeter doesn't do fractions :( I'm getting a new one). The primary coil resistance was also far off on one I bought, which appears to have been returned, and on a used one I got to try out. When checking the ignition system I found some badly worn parts, so the distributor cap, rotor and cap seal were replaced right off the bat. Later when testing the replacement ignition coil, I found that no spark would jump from the distributor to the plug wire but when I cranked it the tach would move - in a very odd erratic way, but it was moving. I only have 1 day to fix this problem so if there's anything else that could be broken I need to replace it. Should I just get the ignition coil exchanged or could something else be causing this? The only thing I could imagine is the wire from the ignition coil to the distributor being broken, but it was running fine just a few hours before it broke down (although with very rough starts) and if it was broken I guess the spark would still jump the gap and wouldn't prevent the car from even sputtering when cranked.
Any ideas?
Assuming this is a somewhat conventional ignition system with some type of ignition driver controlled by some type of pickup in the dizzy, firing the coil, to the dizzy then out the rotor to the plugs. Is that correct?
Get a decent meter. Like a ten dollar one, not a 1 dollar one. That's United States Dollars, not Kazunies or whatever you have down there. Check the resistance of the coil and if it is off from spec that much, get another coil.
Pull the wire from the coil to the center of the dizzy at the dizzy side. Put a #2 phillips in the end of the wire and hold the shaft near a ground like the engine, like 1/8" away. Uh, hold the plastic part of the screwdriver. Have your helper crank the motor. Spark between the screwdriver and the ground? Yes: Problem in the rotor/cap. No: problem with coil, driver or pickup.
A coil works like this: there is +12V to one side of the coil (the '+' side), then there is a 'pulsed' ground to the other (-) side. When the '-' side is grounded, an electrical field builds in the coil. When the ground is removed, the coil fires that energy as a spark through the center terminal, repeat ad infinitum.
You can check for coil pulse this way: stick a 12V test light probe in the '-' or trigger side of the coil. Now spin the engine over; if the test light pulses there is power and pulse, meaning the coil should make sparks. If you have pulse but no sparks, check the coil itself, dizzy cap etc. If no pulse and no sparks, there's trouble in the part of the ignition which controls such matters. I'm not real conversant with Samurai particulars, unfortunately.
Today I got the coil exchanged for a new new pne which had the resistance in the right ballpark and tested to see if a spark would jump from the output wire to the engine head, and it did, but the spark isn't making it through the distributor, so the only electronic doodad in the way that can fail is the igniter.
Also the meter I was using is a Fluke with an LCD readout and an EM field meter...now I gotta find a cheapo that's actually useful.
OK, you don't need a cheap meter if you have a Fluke. I just suggest a cheap meter because that's all you need instead of a $500 meter which some people think will tell you 3 ohms better than a $10 meter will tell you 3 ohms.
Next, if you have spark from the coil lead to the head when you crank it, then your igniter is OK. You either have a very bad cap or rotor or your timing is way off.
Doc beat me to it. If the coil is making sparks then all that stuff is OK and the problem lies beween the coil output terminal and the spark plugs.
Pull the rotor off the dizzy shaft and look REAL close at it. You are looking for a gray sooty 'lightning bolt' pattern, the real thing not the cartoon type. Here's a pic of a spark plug with both cracking and carbon tracking:
.
There are 'flow' marks on just about any ignition part from the injection molding process and that's not the same thing. If you see carbon tracking the spark is 'flashing over' to the dizzy shaft. Heck, IIRC you have an old dizzy, grab the rotor from that and try it
Just earlier today I was thinking that the igniter could be OK...but the rotor and cap are brand new genuine Suzuki stealership parts, and the timing hasn't changed. Also that wouldn't account for the tach flying sky-high while cranking and stuff.
This is really perplexing 
I'll check the distributor shaft also.
edit: Oh another issue...the connector for the #3 spark plug wire at the distributor is missing. I don't know when it went missing either. The graphite conductor is more than close enough to the distributor's connector to jump the gap, and I figure that if it was lost while diagnosing the problem the engine would run on three cylinders or at lesat sputter if everything else was working. I'm going to see if I can build a makeshift connector, but I might have to get some new plug wires.
OK, lets see if we understand your symptoms here:
Engine cranks but doesn't start.
With engine cranking, wire pulled from center of dizzy sparks to ground in a regular rhythm.
WIth the wire hooked back up to the dizzy center and pulling #1 spark wire, no spark to ground when cranking.
Tach jumps around and didn't used to do that when cranking.
Does that sum it up?
Yep that's it...although I haven't done a plug-wire-to-ground test with the new ignition coil, I'll do that tonight. The tach used to jump a little bit when cranking but now it's a lot worse. I've been reading on how to test the igniter, I'll do that tonight as well.
In 99% of cars, the tach triggers from the '-' side of the coil. Long shot: try unplugging the connector for the tachometer. I have seen 2 shorted tachs kill the spark.
Okay I ran some more tests...I'm actually getting tiny little barely noticeable sparks at the plugs on about 1 out of 2 rotations. That would explain some of the pops I occasionally got while testing. Nothing like the nice big fat sparks I'm getting if I let the coil output ground to the head though.
There are 3 wires coming out of the distributor:
Black w/ white stripe that goes into the harness (I think this is the tach signal, I didn't notice if it was something I can disconnect but I'll check - edit: this is the same as the brown wire)
Brown - goes to the negative terminal on the ignitor.
Yellow - goes to the positive terminal on the ignitor.
There's another wire that also goes to the positive terminal on the ignitor, it carries 12V+ whenever the key is in the ON position (I'll call this IGN ON)
With the key in ACC or OFF the power to all these wires is dead. With the key in the ON position I get:
11V from IGN ON + Yellow to Brown
11V from IGN ON to Yellow or Brown
0V between yellow and brown
Same thing when cranking, voltages are steady.
Another thing to note: I tried shorting where the ignition capacitor plugs in to bypass the capacitor in case it was dead (I had that happen on the AE92 and that's how it was solved). When I did this, the IGN circuit fuse blew when I put the key in the ON position. 
Oh and I checked that the distributor shaft didn't have carbon trails on it.
I don't think you really understand the underlying anatomy of your Suzi. I think you need a new cap or a new rotor or your existing rotor is on backwards.
Both are brand new, the engine has never fired with them on, and the rotor only goes on one way. I made sure I put it on in the same direction as the old one.
So, you have spark going into the dizzy on the coil wire but not coming out to ANY of the plug wires correct? If so the only things in the circuit are the cap, rotor, and plug wires. checking the "ignitor" is pointless, it triggers the low tension side of the ignition and we know that is ok from the spark at the coil wire. Make sure the centre electrode on the cap has some downward spring tension, make sure the centre of the rotor has enought height to it to contact the centre of the cap.
There are very weak and seemingly intermittent sparks making it to the plugs...I know it's getting fuel because of the smell after cranking.
I don't know how I could check the clearances in the cap, the rotor on there is just like the old one, and if anything the cap probably sits lower now with the new seal. There are what look like pencil marks in the center of the rotor so I guess it's touching.
I think there could be a problem with the ignitor because I'm getting 11v from the coil power source to either of the wires from the ignitor whenever the key is in the ON position. Whichever wire has the switch on it, it should be off when the engine's not turning, right?
Okay, you should have:
Battery voltage at the '+' terminal with the ignition switched on. Sometimes there is a resistor in the power circuit, if so what you will see is ~ 6V at the '+' terminal with the ignition on but ~12V while cranking.
The '-' terminal should have battery voltage as well when the ignition is turned on and the DVOM is connected between that terminal and ground. Caution: do not ground the '-' terminal for more than a few seconds. The coil is not designed for that and can rapidly overheat. If you connect a test light to ground then touch the probe to the '-' terminal and spin the engine you should be able to see the test light pulse. This is good; this means the igniter part of the circuit is working.
Since you have a hot blue spark from the coil wire but weak intermittent crappy spark at the plugs, your problem is somewhere between the coil wire and the plugs. Here's a really stupid sounding thing to check: is the distributor actually turning and turning properly? Reason I ask, I had a distributor drive gear roll pin shear off in my old Ford Courier (Mazda) pickup and the damn thing had all kinds of goofy popping and banging and stuff like that.
Overall circuit diagram:
Pretty good tutorial on ignition system operation:
http://www.classicspark.com/English%20information/Technical%20infomation/45d-ignition/working-ignition-system-uk.html
Oddly that link won't work after it's posted, but I found the page:
http://tinyurl.com/yrjms2
According to that page the ignitor ground should be switched on only when a spark is firing...to be clear, the test in my previous post was done with the ignition coil totally removed, I was just working with the wires leading to it, so doesn't that mean the ignitor is letting power through when it shouldn't?
I'll double-check the mechanicals as well. I've found a distributor I can try and will probably get a chance to test it out tonight or tomorrow.
edit: After reading through that page I wonder if my new ignition coil could be damaged. It should only get power in 4ms pulses but mine's getting power constantly when the key is in the ON position. The spark from the ignition coil output is fat and orange/yellow. It's never gotten hot. I'll recheck the resistance tonight.
The ignitor works in the same fashion as points: when the points are closed or the ignitor is not getting a signal from the pickup, the '-' side of the coil is grounded. This allows the windings in the coil to build up a charge. Once the points open or the ignitor gets a signal from the distributor pickup, the ground at the '-' terminal is removed. This causes the electrical 'field' in the main windings to 'collapse' and the result is a spark from the main terminal of the coil.
It's possible to test a coil by applying 12V to the '+' terminal, then use a short piece of wire to ground the '-' terminal. Then lift the wire to open the ground circuit. Each time that's done the coil should spit a spark from the main terminal. As I said earlier, don't ground the '-' terminal for more than a couple of seconds because this can make the coil overheat.
Ooooh I see, I had it backwards.
OK I made sure the distributor shaft is in one piece, I checked to make sure nothing's hooked up wrong, it looks like the center pin in the cap is contacting the top of the rotor, but the spark's just not making it through the distributor...if I ground the coil output, sparks are made at regular intervals, so the ignitor should be working...
OK I made sure the distributor shaft is in one piece, I checked to make sure nothing's hooked up wrong, it looks like the center pin in the cap is contacting the top of the rotor, but the spark's just not making it through the distributor...if I ground the coil output, sparks are made at regular intervals, so the ignitor should be working...I just can't wait to try a new distributor in there. This really makes no sense
Oh I found an almost identical problem, but it's on an electronically advanced ignition:
http://www.fixya.com/cars/t591992-86_exp_spark_doesnt_make_distributor
The mechanic says it's something in the distributor. A new one is on the way...very, very slowly.
I dunno if this helps or not, but the 4 wire GM HEI ignition module is cheap, readily available and can be wired into damn near anything that has a magnetic pickup coil. They look like this:
Here's a schematic where one was used in a Jeep:
