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Need expert on Mopar 5-pin electronic ignition, mid-'70s

General engine tech -- Drag Racing to Circle Track

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seattle smitty
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Need expert on Mopar 5-pin electronic ignition, mid-'70s

Post by seattle smitty » Mon Jun 25, 2012 11:27 pm

This is driving me nuts, because it should be quite simple, so simple that even I should be able to work it out myself . . . but, Noooooo . . . !!!

The project is an old Sears garden tractor, early '70s, that has lots of attachments including one with which I mow the lawn (which is now knee-high). Tecumseh single OHV, 14hp, 20A alternator. Tecumseh is out of business; somebody is said to be trying to get it going again but so far parts are NLA, including the magneto/CD ignition module which died.

The popular fix for those in the know is to forget the mag and adapt a Chrysler 4-pin ignition module and an automotive coil. The fellow who is most into this, Ed Stoller, has been experimenting with this for some years and makes, bench-tests, and sells his own pickup/sensor. This consists of a small ceramic button magnet bonded to a soft steel bolt with about 400 turns of fine wire, one end attached to ground, the other to one of the 4 pins on the Chrysler switchbox. The second of the two pickup connections on the Chrysler box is not used with Stoller's system, but it works fine on the few hundred conversions that have been done, and so far as I know it has nothing to do with my own issues.

Stoller's pickup-coil was designed to make use of the peculiar Tecumseh flywheel. Tecumseh press-fitted two 3/8" steel dowels partway into the periphery of their flywheel to trigger their mag/CD ignition (the windings for the mag being located under the flywheel, as are the alternator windings). The leading pin, that is, the pin that passes under the pickup first, sits up higher than the second pin, and one sets the gap to this pin with a feeler-gage in the usual way. This first pin is for starting, and fires the plug at about TDC. Once the engine starts and spins up past about 550rpm, the pickup is then for some reason able to sense the second pin, which is pressed into the flywheel farther (so, more gap), and which fires the plug at the running advance of about 17 degrees BTDC, I believe.

Now to my own mystery problems:

Rather than spend cold cash on a 4-pin Mopar set-up, I dug into my old dusty boxes and got out a never-used example of the earlier 5-pin ignition, complete with a new harness and a used ballast resistor, and also a good, oil-filled coil. This happens to be a mid-'70s "blue box," which was represented to me at the time, by a dealership, as the NASCAR version, which they said put out the same spark as the standard box but had components that would stand up better under heat.

Now, the ballast resistor for the 5-pin box was a special item with two resistors, four male connectors. This seems to get some people baffled and worried for no good reason. One of the resistors is the actual 1.2 ohm ballast resistor that protects the coil while the switch is in the RUN position, and is bypassed while in the START position, the normal deal. The second resistor is not a ballast at all but some sort of surge-protector for the circuitry in the module, and it is used whenever the switch is on. The later 4-pin ignition simply put this surge-protection inside the module and eliminated the "extra" outside resistor. I can think of no reason why a 5-pin box can't serve my purpose just as well as the favored 4-pin box (Ed Stoller's set-up also uses a coil with an internal resister, but I don't like them as well and don't mind the slight additional wiring complexity).


BUT, BBUUUUUTTTT, something is amiss! I'm sure I must have something connected wrong, but I'll be danged if I can see what it is!

On the tractor, I have an on-off 12V/20A switch for RUN, which takes 12V from the battery positive post, through the switch, through a fuse-holder with a 10A fuse in it, and on to the 12V input pin which is at the apex of the five pins in the module.

To run the starter motor, I'm using a 3-post type of solenoid; two heavy posts for the big cables on either side, and a single small post in front. On a 3-post solenoid, this small single post is always hot; by connecting it to ground through the START circuit, it makes the contact between the big posts. However, in my case I am not using this post at all, because this is one of the fine old solenoids that has a mechanical button on top which I push with my thumb to start!!

At the power post of the starter I've connected my wire that bypasses the ballast and sends 12V direct to the coil.

I should also state in advance that all wiring and connections are new and good, and that all of the grounding from the case of the module to the frame AND direct to the engine block (AND direct to Ed Stoller's ignition pickup), and from the block to battery negative post are excellant.

NOW . . . for some reason, when I switch on the RUN circuit, and then put my thumb on the starter, the engine fires right off, and it will run along just fine, at low rpms, as long as I hold my thmb down and have power to the starter. When I let off the starter . . . silence. This is ordinarily a sign that you have an open ballast resistor, thus no connection to the coil in the RUN mode. But I have checked the resistor with an ohmmeter and not only have continuity but both resistors read about the same ohms as a new off-the-shelf resistor. In case the surge of current might be causing the resistor to open in a way not testable with the ohmeter, I simple ran a jumper-wire across the resistor. But the symptoms did not change.

The second clue (and here is where i'm hoping one of you will have the "aha" moment that saves my project): I keep blowing the fuse in the RUN circuit. As I understand it, the module only ought to be drawing about 3A normally, and a 5A fuse should be appropriate, but I am blowing 10A fuses. WHY??? I wouldn't have thought I could fry something in a never-used module, but maybe I did when I was sorting out the connections, so, does anyone know if this box has a failure mode that would, say, create a dead short through the 12V input pin to ground under load?

The pickup and the ignition do work. The engine is trying to run. What have I done?

Thanks for your patience :lol:. Eagerly awaiting your solution =D>

--Smitty

bill jones
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Re: Need expert on Mopar 5-pin electronic ignition, mid-'70s

Post by bill jones » Tue Jun 26, 2012 12:23 pm

-I just did 5 pin Chrysler project over the weekend and had to wire the system to run on my ignition machine.

-here is my wiring notes which also includes a picture of a Chrysler 5 pin wiring diagram off the internet--that leaves out details such as trigger polarity orientation of the trigger wires--and doesn't mention which end of the pentagon wiring plug you are looking at.

-I spliced 4 colored wires onto my pentagon wire connector which only had about 6" worth of original wires.

-maximum amperage thru this system is right at 4.0 amps--which happens when key is on and there is no rotation of the distributor----then is drops to about 3 amps at idle and declines to about 1 amp at 5000 rpm (when firing 8 cylinders).
-----------------------------------------------------------------------------------
wiring up Chrysler chrome box on my machine---parts involved are:
1-stock Chrysler black coil
2-Chrysler chrome box
3-my wiring harness which includes:

-a Chrysler 5 wire pentagon shaped plug for the ignition box with 5 wires long enough to
fit my distributor machine.

A-a two terminal plug to fit the Chrysler distributor magnetic trigger plug.
-male is white (but usually orange) & positive----connects to CW 1st wire down on right hand side of pentagon connector looking at the outer end of the plug

-female is black & negative out of distributor---connects to CW 2nd wire down on right side.

-these same two wires as they come out of the magnetic trigger coil---black is on the top and the white (or orange) is underneath the black.

B-one short wire connects to coil negative.
C-one yellow wire to connect to the 5.0 ohm side out bottom of the dual resistor.
D-one orange wire to connect to the 1.3 ohm side out bottom of the dual resistor.
E-one red wire that connects to 12 volts when key is on.

4--a 4 terminal dual resistor with a notch denoting the bottom for this description.
-5.0 ohms are the two terminals on the left side.
-1.3 ohms are the two terminal on the right side

-top two terminals are connected together and to 12volt when key is on.

-bottom left is 5.0 ohms out of resistor---connects to yellow wire
-bottom right is 1.3 ohms out of resistor---connects to orange wire and to coil positive
-----------------------------------------------------------------------------------------------------------------
----looking at the outside of the 5 wire pentagon shaped connector when it is installed onto the ignition box.

1---top wire of connector gets full 12volts when key is ON

2---CW 1st wire down on right hand side of connector = MAGNETIC TRIGGER pos----male on plug
3---CW 2nd wire down on right hand side of connector = MAGNETIC TRIGGER neg--female on plug

4---CW bottom wire on left hand side of connector = gets output end of the 5.0 ohm side of dual resistor.
5---CW top short wire on left side of connector = goes directly to the coil negative terminal.
--------------------
6---coil positive gets the output end of the 1.3 ohm resistor side of the dual resistor
-----------------
7---the box itself needs to be grounded which is typically done thru the mounting fasteners to body metal.
-----------------------------------------------------------------------------------------------------------------
-this schematic shows the 5 wire pentagon plug disconnected from the ignition box where you’d be looking into the female receptacles of the plug rather than at the outside of the plug as I have described in my wiring,

-notice that my numbering of the 5 wires is also different than this picture---in particular #4 and #5 are reversed---and I wired my dual resistor upside down compared to this picture.

-This about all I know about the stock 5 pin wiring---and it works perfect.
--------------------------------------------------------------------------------------------
mopar 5pin ign.jpg
------------------------------------------------------------------------------------------------
-several side notes---I also tested this particular distributor using an MSD6al with same stock coil and a test cap that has holes to where I can look inside.

-The metal frame and the magnet itself of the magnetic trigger area about an inch long by about 3/8" wide and is only about 5/8" below the rotor.

-when Msd system is running and the rotor tip passes over this metal ground source the spark really would rather jump down to that metal than run down the plug wire to jump a plug gap.

-this doesn't happen when the plug gap is narrow---but as soon as the gap is widened out to put a load on the secondary system the sparks immediately takes this diversion to ground.

-Personally I would epoxy the entire top of all of the metal with a non conductive epoxy.
-----------------------------------------------------------------------------------------------------------------
-while testing this 360 distributor I also was looking at the rotor and reluctor index and found them both to be off enough to cause the sparks from the rotor tip at the inner cap terminals to be off to the side about 3/16".

-the reluctor has two slots for the locating pin to the rotor shaft---one is slot is specifically for CW rotation and the other is for CCW rotation.

-just happened the reluctor had been installed using the wrong locator slot--which creates something close to 10 degrees of rotor and reluctor index.

-reluctor index is nearly dead nuts aligned timing happens but just slightly past perfect alignment to the magnets vertical strip---which is a normal trailing edge trigger like I see on Fords and HEI's.
----------------------------------------------------------------------------------------------------------------
-another issue was the white colored rotor gap to the inner cap terminals seemed way too wide for my liking---got to looking at it closer and compared it to a black rotor and found the black to have a slightly longer metal tip.

-I pulled the retaining pin out of the rotor--made a longer tip and installed it and checked it the for rotational interference and trimmed it down to fit with about .040" minimum clearance.

-But my test cap with holes in it showed me the inner terminals definitely were not centered, so there was like .040" gap on one side of the cap and about a .090" gap across on the other side of the cap.

-got to looking at the center button area of two caps and found that both were obviously not centered.
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Barry_R
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Re: Need expert on Mopar 5-pin electronic ignition, mid-'70s

Post by Barry_R » Tue Jun 26, 2012 4:42 pm

Just got off the phone with my electronic guru buddy for the stars - the revered and world famous Tim Young. He was reading this thread but could not respond from the underground test labs at a government agency so secret that their acronym has an acronym and their name badges are written in code (he will promptly need to kill me for that intro.. :) )

He says that the problem lies in the resistor bypass wire to the starter. The bypass needs to be done through a dedicated relay to prevent backfeeding.
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seattle smitty
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Re: Need expert on Mopar 5-pin electronic ignition, mid-'70s

Post by seattle smitty » Tue Jun 26, 2012 4:56 pm

Really!, hmmm, gotta think on that one, first I've seen of that. But easy enough to do. Thank him for me, and thank you, and I will report back when I get a relay and wire it in. And thanks to Bill; your diagram of the wiring of the resistor, et al, is like what I went by.

Is there any sort of on-line source on this ignition, a wiring diagram of the module, anything printed?

seattle smitty
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Re: Need expert on Mopar 5-pin electronic ignition, mid-'70s

Post by seattle smitty » Thu Jun 28, 2012 7:08 pm

Reporting back . . . IT WORKS!! Bless you Tim Young, and Barry, for your tip. Wiring a relay into the bypass circuit did the trick. No more blown fuses, the engine runs. Runs better than it ever did, with never a misfire even on an old cruddy sparkplug, and I was able to mow about half of the grass (in "compound-Low;" that grass was TALL!!!). You know how with most small engines when you take the plug out to see if there's a spark you have to get real close to peer at the plug, with one hand shielding it from the light while you pull the engine through with your other hand, . . . and if there is a spark you can barely make it out? This Chrysler box throws big fat blue sparks that you can see in bright sunlight three feet away, and this with an old plug with lots of deposits! When I get a new plug I can probably double the gap and maybe lower the fuel-burn a little. The elimination of misfires already is helping in this regard.

Thanks again, . . . from my neighbors as well :lol: Thanks to Ed Stoller as well, who developed the trigger. Incidently, since i find I can't edit my opening post above, his trigger uses a rare earth, not ceramic, magnet, and has a diode in the the circuit.

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Re: Need expert on Mopar 5-pin electronic ignition, mid-'70s

Post by Schurkey » Fri Jun 29, 2012 1:33 pm

seattle smitty wrote:Stoller's pickup-coil was designed to make use of the peculiar Tecumseh flywheel. Tecumseh press-fitted two 3/8" steel dowels partway into the periphery of their flywheel to trigger their mag/CD ignition (the windings for the mag being located under the flywheel, as are the alternator windings). The leading pin, that is, the pin that passes under the pickup first, sits up higher than the second pin, and one sets the gap to this pin with a feeler-gage in the usual way. This first pin is for starting, and fires the plug at about TDC. Once the engine starts and spins up past about 550rpm, the pickup is then for some reason able to sense the second pin, which is pressed into the flywheel farther (so, more gap), and which fires the plug at the running advance of about 17 degrees BTDC, I believe.
First Guess: Flywheel rotates the opposite direction.

I don't know how the LEADING pin can provide retarded timing, while the FOLLOWING pin can provide advanced timing. Spin the flywheel the other way...and the first (shorter) pin provides advanced timing, the following (longer) pin provides retarded timing.

I'd think that this system would "multi-spark" at any engine speed high enough for the short pin to trigger the module. If the short pin can trigger the "advanced" spark, the longer pin would still trigger a second, retarded spark.

seattle smitty
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Re: Need expert on Mopar 5-pin electronic ignition, mid-'70s

Post by seattle smitty » Sat Jun 30, 2012 12:19 pm

You're right, of course. Brain-fade on my part.

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