I am stuck here.
engine is not starting. engine stopped all of a sudden while adjusting engine (see thread on AFR and distributor). I experience no spark. Once in a while there is some spark but not consistent meaning intermittent .
Pulled the center cable from distributor..... no spark against ground when cranking. No voltage at coil (between + and - terminal), not in key position 2 (run), not while cranking in key position 3 (start).

I assume either o.6 Ohm resistance or switch gear are faulty. Is this correct?

I am lost. Can anyone help me troubleshoot? Need to get this car on the roads of Oman again.

Martin

Martin, are you checking for voltage between engine/battery ground and coil terminals or are you checking between the coil terminals?

Negative lead of the voltmeter to negative post of the battery and positive lead to coil terminal. Then do a double check using the engine block as the ground.

__________________
“Whatever story you're telling, it will be more interesting if, at the end you add, "and then everything burst into flames.”
― Brian P. Cleary, You Oughta Know By Now

have you another coil lying about to try?
Are you sure the engine block ground ( main ground) is OK , was this moved in the head rebuilding

__________________
Ron
2015 Porsche Cayman - Elizabeth
2011 Porsche Cayman - Bond,James Bond
Sadly MERCEDESLESS - ALways LOOKING !
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14 38HP John Deere 3038E Tractor -Mean Green
84 300SD, Benjamin -SOLD
71 220 - W115-Libby ( my first love) -SOLD
73 280 - W114 "Organspende" Rest in Peace
81 380 SL - Rest in Peace

Hi Mike, I was exactly testing this. Was negative yesterday (mostly)
The block has a solid ground.
I took out the switch gear. It is in my hands.

the plug on the bottom has terminals 15, 16 and 7
Terminal 15 = input from starter switch (plus a 0.4 Ohm resistance) The same connection goes the starter motor... starter is working so I am sure this wire is hot when key in Pos.3 (start).

This means at least during start there has to be + 12V at Terminal 15.
I guess that there is also +12V in Key Position 2 (drive)...must be.
I'll first check these two.

Terminal 16 is the output to the coil (+12V at Coil terminal) with a 0.6Ohm resistance in between. I'll see if this terminal has output.

Terminal 7 is the output to the distributor. This wire that goes into the upper/side of the distr... not sure if this is also +12V...
What is this switch gear doing? How is it working? what for?

No spare coil!
I am almost certain the engine block has ground. I never remove the main ground cable in the back of block.

W:

With all respect, both to you, and to a number of other folks who will gladly help you through a process of analysis, it may be expeditious for you to select one of the many who are qualified to be your interlocutor. Speaking with one analyist, rather than many voices, may streamline the process.

yes I am sure this would be best. Who can do it?

Well meanwhile I have the switch gear out but don't quite understand what this thing is doing (how it is working).
Both resistances are good. Due to the 0.4 Ohm resistance only + 8.6V are showing up at terminal 15 at switchgear... then from terminal 16 the voltage gets further reduced by the 0.6 Ohm . I measured only + 3.2 V at the coil (this is with key in position 2 (drive). It gives just a very weak test light... The bulb is glimmering a bit that's it.
I don't know if this is supposed to be this way.

I put the fuse for fuel pump in...engine is not starting.
Can someone guide me through the switch gear and ignition Gremlin?

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Frank's elected by popular and almost unanimous accord Get 'em Tiger!

__________________
“Whatever story you're telling, it will be more interesting if, at the end you add, "and then everything burst into flames.”
― Brian P. Cleary, You Oughta Know By Now

go Frank

__________________
Ron
2015 Porsche Cayman - Elizabeth
2011 Porsche Cayman - Bond,James Bond
Sadly MERCEDESLESS - ALways LOOKING !
99 E320 THE Queen Mary - SOLD
62 220b - Dolly - Finally my Finny! Sadly SOLD
72 450SL, Pearl-SOLD
16 F350 6.7 Diesel -THOR
19 BMW X5 - Heaven on Wheels
14 38HP John Deere 3038E Tractor -Mean Green
84 300SD, Benjamin -SOLD
71 220 - W115-Libby ( my first love) -SOLD
73 280 - W114 "Organspende" Rest in Peace
81 380 SL - Rest in Peace

Do you have a spare switchgear as you call it? The one on my 4.5 died due to improper dwell once (before I ever started driving or working on it) and another died due to me leaving the key in the run position too long without it running (noticed the resistor smoking hot but it was too late by then). You can get a condensor setup & bypass the switchgear if you need if it's toasted.

__________________
Current:
2021 Charger Scat Pack Widebody "Sinabee"
2018 Durango R/T

Previous:
1972 280SE 4.5
2014 Jeep Grand Cherokee Limited "Hefe", 1992 Jeep Cherokee Laredo "Jeepy", 2006 Charger R/T "Hemi"
1999 Chrysler 300M - RIP @ 221k

Tomguy is right as well, by pass it and give it a shot. I have a few lying about if that helps , not sure of the vintage tho. I think one is off an 83 380, probably the closest I have

__________________
Ron
2015 Porsche Cayman - Elizabeth
2011 Porsche Cayman - Bond,James Bond
Sadly MERCEDESLESS - ALways LOOKING !
99 E320 THE Queen Mary - SOLD
62 220b - Dolly - Finally my Finny! Sadly SOLD
72 450SL, Pearl-SOLD
16 F350 6.7 Diesel -THOR
19 BMW X5 - Heaven on Wheels
14 38HP John Deere 3038E Tractor -Mean Green
84 300SD, Benjamin -SOLD
71 220 - W115-Libby ( my first love) -SOLD
73 280 - W114 "Organspende" Rest in Peace
81 380 SL - Rest in Peace

Thanks gentlemen; I'll try to rise to this.

Function of components:
The switchgear is a transistorized current switching device that relieves the distributor contact points of high current. The current carrying transistor in the switchgear is signaled (biased) by the opening and closing of the contact points. The transistor carries the coil current, rather than the contact points. Pin 15 is the power supply to the switchgear (B+). On open circuit, voltage at pin 15 will be 12V with the ignition switch in position 2. (When running, the voltage will be less than 12 due to the presence of the .4 ohm resistor in the circuit). Pin 16 is the ground for the coil primary; it is switched to ground by the transistor. W, I would like a point of clarification here; your schematic shows the switchgear transistor carrying the positive side of the coil primary circuit rather than the ground. Is that confirmed? Pin 7 is the signal line from the contact points, and carries only a very low voltage/current trigger pulse.
Resistors: When running, the coil primary circuit is provided with a total external (external to the coil) resistance of 1 ohm via .4 and .6 ohms in series. When starting, (ignition switch in position 3) the .4 ohm resistor is bypassed to provide increased voltage to the ignition system (because the whole car system voltage is being drawn down by the heavy demand of the starter motor).
Tests:
Unplug the switchgear (one plug or two?). Remove the positive lead from the coil primary.
With the ign. switch in pos. 2, there should be 12V. at the pin 15 socket in the plug and at the lead removed from the coil. If not, jiggle the ign. switch and all wires that you can reach that are part of the primary circuit. Any changes? The ign. switch is a possible suspect area; the wires somewhat less so.
Connect an ohmmeter across the center terminal of the pin 7 plug and the body of the distributor. With the engine rotated such that the contact points are closed, the resistance in the trigger circuit should be zero. Is the capacitor (condenser) still installed in the distributor? If it is shorting intermittently it will shut off the ignition. It is needed only for RFI suppression, not for ignition function, and may be disconnected/removed. If the pin 7 resistance check shows above zero or an open circuit, wiggle/flex the cable from the dist. to the plug. That cable is a common failure source.
Disconnect both leads from the coil. Check the coil internal resistance; it should be on the order of .35-.45 ohm. If the resistance is either very low (near zero), or if the primary is very high or open, the coil is the likely culprit. If you can, jumper the isolated coil to 12V thru the .6 ohm resistor on the positive terminal, and to ground on the negative. Keep the connection for no more than one minute; the coil should be quite warm to the touch. If the coil does not warm, you may have found the problem.
If none of the tests shows a defect, the switchgear is probably defective. If that seems to be the case, a non-switchgear ignition arrangement can be made. Details at 11!
Good luck.

See Martin, ask the right guy and you'll get the right answer!

Thanks Frank.

__________________
“Whatever story you're telling, it will be more interesting if, at the end you add, "and then everything burst into flames.”
― Brian P. Cleary, You Oughta Know By Now

An edit to post #12 (above) seems in order.

The schematic included by the OP is certainly the correct one for the model year, hence, the switchgear is indeed in the power (positive) side of the coil circuit, rather than the ground side.

The tests will be a bit changed because of that. With the plugs removed from the switchgear, and the ignition switch in position 2, 12V should be present at the plug socket that corresponds to pin 15, but no power at the coil positive terminal. With the four-pin plug reinstalled, but not the single pin plug, there should not be power at the coil positive terminal. When pin 7 (the single pin) is grounded with a jumper, there should be power at the coil positive terminal. Grounding and ungrounding pin 7 replicates the closing and opening of the distributor contact points. CAUTION: Have the coil secondary lead installed and grounded (or connected to a spark plug) when grounding and ungrounding pin 7. If everything is working there will be sparks.

If all other components have checked out OK, and there are no sparks or power to the coil positive, the switchgear is the likely suspect.

Thanks Frank: now we are diving is...
Switch gear has ONE main plug (3 flat pins : #16, #15 and #7... as shown in the schematics, I'll attach pics) Power feed from ignition is #15 with a 0.4 Ohm resistance upstream (I don't see how this 0.4 Ohm can be bypassed?) #16 is the output to ign. coil (+ terminal) with the 0.6 Ohm in between (NO GROUND!). I believe the 2 resistors are pulling down the voltage at the coil?
#7 is the input from distr. (pulse from point as you said)


Test 1 :"With the plugs[ there is one plug] removed from the switchgear, and the ignition switch in position 2, 12V should be present at the plug socket that corresponds to pin 15, but no power at the coil positive terminal."

Answer: NO....there is 8.6V at plug socket # 15 (not 12V). I think this is due to the resistance (0.4Ohm?- I am not an electrical engineer).
No Power at coil- correct- because Pin 16 is disconnected

Test 2: "With the four-pin plug reinstalled, but not the single pin plug, there should not be power at the coil positive terminal."
'When pin 7 (the single pin) is grounded with a jumper, there should be power at the coil positive terminal. Grounding and ungrounding pin 7 replicates the closing and opening of the distributor contact points. CAUTION: Have the coil secondary lead installed and grounded (or connected to a spark plug) when grounding and ungrounding pin 7. If everything is working there will be sparks.'

Answer: Not sure what you are saying. Switch gear has a 3 pin plug. There is no single pin plug, see picture. You can connect only all 3 by reinstalling the plug.
I did the following test: plug is pulled, the I connected the switch pins #15 (switchgear) and corresponding #15 of plug. And the same with #16 . Key in #2. Pin #7 disconnected
Result: there is no power at coil (no test light).

Then in addition I grounded Pin7 of switch gear: Light is going on (very shy: around 3V). Interestingly... when I take the ground cable off Pin 7 the test light is shining bright for a blink of an eye: like a spark. And it makes some sound. I think sound comes from distributor cap. So there might be a spark.

Went out again, pulled the central cable at the distributor cap...connected #7 to ground, disconnected and Ouch. Yep, spark!
This means the switch gear is operating as it should?

If yes... then the pulse from distributor is suspect, correct? How can I test the pulse from distributor?
Martin

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