Please explain "start" circuit to me

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all the interlock is is a extension of the neutral safety switch wiring, it has no power thru it.
 
Gentlemen, at this point, I am completely bumfuzzled.
Aaron and I checked various wires for good connections, cleaned and re-seated the bulkhead connectors, checked vacuum lines, and it still would not fire. We disconnected the interlock switch, and still no go. We put the key in "run" position and cranked the engine by crossing the battery terminals (to by-pass the ignition switch, just in case). We swapped out a new ECU and a new coil. Nothing made a difference.

Then, we noticed that releasing the key from the "start" position to return to the "run" position would cause a slight backfire through the carb. That indicated there was that moment where a single spark occurred as voltage surged through the "run" circuit. Hmmmmm.....

We changed the *&$%_@+~ ballast resistor and it popped right off. Purrs like a kitten. What the heck????

I can't count the number of times I have read and been told, "If the ballast resistor goes bad, the car will start, but will then stall and die when the key is released." That appears to be an old wife's tale. This car would not start at all, period, with a bad ballast resistor. We swapped the old coil and ECU back in, just to minimize the variables. It fired up on the first turn of the starter.

In the morning, we will see...

Thanks to all for your input,
Jerry
 
Good to read you got it fixed. From what you wrote in the first post, it didn't appear to be getting any power to the coil at all in any key position.

That's what I love about trying to diagnose stuff over the net. Stuff that normally takes 5 minutes to figure out, takes hours.

At least it's up and running!
 
There was a time when owners would dive into replacing the timing set over a bad ballast resistor. Happy moparing :)
 
Good stuff guys. Anyone have any pics of this interlock plug and it's location as well as the "Red Button" for those of use that are wanting and needing an education? Thanks guys and good luck with your efforts.
Small Block
 
Hey, five hours to fix a problem by using you guys to sound off on is a blessing. Sure beats leaving the car at some shop for a few days and spending a couple of hundred dollars for them to fix it with a $8 part. At least Aaron and I learned something else about his car. Now, he knows how to quickly fix it the next time this happens.

'74 Sport said:
With the ignition tester connected to the coil's primary wire and grounded to the body, we get a single spark when the ignition key passes the "run" position, then there is no spark as it gets to the "start" position as the engine cranks.
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This is how I tried to explain what we were observing. What it meant, I did not know. You may have noticed that I sometimes get a little long-winded in my responses. Often, the detail may get lost in the rhetoric.

Regardless, I appreciate any help I get,
Jerry
 
Now you know a ballast resistor can fault in 2 ways, either burned to open circuit or to grounded circuit through the firewall or its mounting bolt.
 
Jerry
Get Aaron a spare to keep in the glove box. I have seen "new" ones only last 6 months (or 20 years). $8 is cheap insurance. Or better yet convert him to HEI, its SOOO much better and NO ballast resistor.
Frank
 
66aCUDA said:
Jerry
Get Aaron a spare to keep in the glove box. I have seen "new" ones only last 6 months (or 20 years). $8 is cheap insurance. Or better yet convert him to HEI, its SOOO much better and NO ballast resistor.
Frank
Click to expand...

I wont argue with keep a spare resistor in the glovebox. Nobody keeps gloves in there anyway. I will disagree with HEI being SOOO much better.
Ford, GM, Honda, evey mfgr, who placed the ECU and or coil in or on the distributer had increased numbers of temperature related failures.
 
RedFish said:
Now you know a ballast resistor can fault in 2 ways, either burned to open circuit or to grounded circuit through the firewall or its mounting bolt.
Click to expand...
I need to study this ballast resistor a bit to learn more about how it functions.
The mounting screw goes through the center of the ceramic block, so it is completely insulated from grounding to the body. On the back, one resistor coil is embedded in ceramic, so I can't see how it is constructed (time for a hammer). The other resistor (suspected bad one because of the soot) is a ceramic rod spanning across the gap with a very thin wire coil wound around the rod. I need to see if the "start" circuit goes through the exposed coil or the embedded one.

Get Aaron a spare to keep in the glove box.
Click to expand...
Funny, that's where we got the one to swap them out. He had one in there, but we didn't equate the "diagnosis" to the "symptoms". Again, word was that the car would start with a bad resistor, just not run. #-o

Anyone have any pics of this interlock plug and it's location as well as the "Red Button"
Click to expand...
I'll try to do that this weekend. I believe this was a '74 one-year-only system.
 
I bet you have a 4 prong ballast resistor? If so, those are harder to diagnose than 2 prong. They have primary and secondary resisntance.
 
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