A friend hooked his coil up backwards...

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KnuckleDuster

KnuckleDuster

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What would it fry, if anything?

Trying to help him find out why he has weak spark from his coil and the car won't fire unless jumping the positive coil post to starter relay positive, which we only did once for about 2 seconds just to test.

He has the battery in the trunk, and has hooked the IGN 1 start wire to a toggle switch. Gonna probably replace the ignition switch in the column, but want to find any other problems first.
Ballast resistors tested good, all three he had. Tested and tried two different coils as well. Gonna trace through the system and check all ground, plus add a ground strap from engine to fire wall. I think he bought a battery cable, would a braided strap be better?
Any advice is appreciated.
 
Braided is no better, size for size, than any other cable. Measure coil + voltage while cranking. Should be 10V minimum, more is better

Ignition "run" (IGN1) goes dead during cranking. You must have IGN2 (usually brown) hooked up which comes from the switch, through the bulkhead, and to the coil+ side of the coil

What are you using for ignition system? Mopar ECU MUST be grounded to operate
 
AND, hooking the coil up backwards won't hurt anything.
I know it was said the ballasts tested good but I would still jump across it bypassing it and see if it runs like that.
If it does then the ballast is also causing a problem.
Also, as Del said, you have to have ign 1 and ign 2 both powered.
Ign 1 needs power at the key on position, and ign 2 has to have power in the crank position.
 
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I will have to re-test, but I want to say we got 8.4 cranking. I suspect a bad ground, but not sure what he did under the dash with the ignition switch and toggles for start, fan, and fuel pump.
I remember the voltage changed if I turned the cylinder to crank and hit the toggle, vs. just the toggle, if that tells anything. I am not the best at electrical, but always willing to learn more and really want to help the guy out.
 
There's been tons written on here about voltage drop. Problems at the ammeter connections, the bulkhead connector, and even the ignition switch connector and the internal switch contacts. 8.4 is kinda low. I should have asked you to read the voltage "cranking" right at the battery as well. Maybe it's low on charge

Trunk mount? Cables, connections, cable size, ground to body/ battery etc
 
Thanks, I have read a few threads you posted on. Some good info. I had to ask about the coil and ignition modifications.
He has a 75 FSM, but man, those multiple page wiring diagrams SUCK! ...there's all the seatbelt interlock crap, too. I think it has been disabled before he got the car, but it's more to wade through. I am not yet clear on how that whole sytem worked.
 
most will simply twist ign 1 and ign 2 together when using other than OEM ignition and/or temporarily bypassing the OEM ign switch. This would overheat the OEM coil eventually.
Stuff like seatbelt interlock interrupts starter relay operation on the positive ( yellow wire ) side of the circuit much like the neutral safety switch interrupts the ground side of the circuit.
 
KnuckleDuster said:
Thanks, I have read a few threads you posted on. Some good info. I had to ask about the coil and ignition modifications.
He has a 75 FSM, but man, those multiple page wiring diagrams SUCK! ...there's all the seatbelt interlock crap, too. I think it has been disabled before he got the car, but it's more to wade through. I am not yet clear on how that whole sytem worked.
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There is certainly good and bad about the 73/ later "multipage" diagram. One way to simplify this is to download the aftermarket diagrams at MyMopar. They are under "wiring." These are not always correct or complete, but they are a "line" drawing, only two pages, which you can print and tape together. So they are somewhat easier to follow. They omit a lot of stuff including the seat belt stuff

All you need do to bypass that, if it has not, is to tie the two yellows together at the reset relay box under the hood

relay.jpg
 
Long story short, retested and we were losing voltage under the dash. Bypassed the ammeter and it cranks and runs in start but dies if you let off the key to run.
 
Fires in "crank", dies in "run" is the classic symptom of a broken ballast resistor. Measure it w/ a multimeter. Should measure ~0.5 ohm. 1975 might have 2 resistors. If so, the 2nd one is for the ECU power and should measure ~5 ohm. Regardless, I bet you'll measure the one the goes to coil+ measures infinite.
 
KnuckleDuster said:
Long story short, retested and we were losing voltage under the dash. Bypassed the ammeter and it cranks and runs in start but dies if you let off the key to run.
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There are only two wires you need to worry about for now. Refer to the service manual or diagram. It's the IGN1 coming off the ignition switch and IGN2 Colors vary over the years, but dark blue is tradional for no1, "run." This should be hot in "run" but NOT crank. IGN2 is hot ONLY during crank, is traditionally brown.

IGN1, run, blue, feeds from the key out through the bulkhead connector into the engine bay, and feeds several loads, depending on year. Ballast resistor is one

IGN2, brown, "bypass" only goes one place......feeds from the ign switch, out through the bulkhead connector to the coil + side of the ballast resistor
 
You can check voltage at the ignition switch connector coming out of the column. Look the colors up in the manual
 
I won't get back to the car until the owner gets back from vacation in a week.
He wanted to install a new ignition switch so we pulled the column and did, it's still out. I wanted to test more first but it's not my car, and he was hellbent on it.
While it's out I want to dunk the dash side of the bulkhead connector in salt and vinegar to clean it.

We tested the resistance on the ballast, but we did that cold, not after it was working. All three he has checked out good cold.
What's the best way to test the rest of the wiring without battery voltage on the system? What readings am I looking for?
I don't know why I have such a hard time getting my head around wiring, it's like the longer I look at it the more confused I get. I need to go step by step, but especially with him there giving high energy input, we end up bouncing around. I made my way through rewiring most of my car, but I was by myself and able to take my time. Thanks for all the patient help.
 
The bulkhead connector is a source of constant problems. Worst are the large BAT and ALT feed-thrus which often overheat and melt the plastic, causing things to touch which shouldn't. Best is to bypass that within the engine bay (search "MAD Bypass"). It disables the dash ammeter, but cars haven't had those since 1980's - use a cigarette lighter voltmeter. Only exception is 1963 & 1965 cars w/ buss-bar feed-thrus. The female terminals also often come loose and push in so you get erratic or no connection. You can bend the latches to correct. Cleaning is prudent, then fill w/ silicone grease.

Wiring is fairly simple to follow in these cars, just put your pencil on a wire and follow it thru the schematic, noting color and gage. The main theory to understand is that only current flows. Voltage is like a pressure in a fluid pipe. If two locations are on the same wire with no resistance or component in between, they will see the same voltage. The other thing to understand is power = current x (voltage drop) and that turns into heat.
 
BillGrissom said:
The bulkhead connector is a source of constant problems. Worst are the large BAT and ALT feed-thrus which often overheat and melt the plastic, causing things to touch which shouldn't. Best is to bypass that within the engine bay (search "MAD Bypass"). It disables the dash ammeter, but cars haven't had those since 1980's - use a cigarette lighter voltmeter. Only exception is 1963 & 1965 cars w/ buss-bar feed-thrus. The female terminals also often come loose and push in so you get erratic or no connection. You can bend the latches to correct. Cleaning is prudent, then fill w/ silicone grease.

Wiring is fairly simple to follow in these cars, just put your pencil on a wire and follow it thru the schematic, noting color and gage. The main theory to understand is that only current flows. Voltage is like a pressure in a fluid pipe. If two locations are on the same wire with no resistance or component in between, they will see the same voltage. The other thing to understand is power = current x (voltage drop) and that turns into heat.
Click to expand...


Here's what looks like a pretty good primer for novices.
Classic Car Electrical - Short Circuit | Hagerty Articles
 
From what I remember from Auto tech, hooking it up backwards will make it spin backwards...Just kidding ;) I think with a coil it may be higher resistance if hooked up backwards, which could "heat up" things in the circuit.
 
Dartswinger70 said:
From what I remember from Auto tech, hooking it up backwards will make it spin backwards...Just kidding ;) I think with a coil it may be higher resistance if hooked up backwards, which could "heat up" things in the circuit.
Click to expand...

Backwards coil does not change resistance. It can cause poor performance because of the spark shall we say profile, as well as polarity.

See, it gets complicated. The coil is a transformer, with two windings, but the secondary (high voltage) IS NOT GROUNDED to the can. The low end of the secondary is interconnected to the primary
 
If you connect the coil backwards, I understand that the electrons will then flow from the spark plug electrode to the ground electrode. The later is mild steel and will quickly degrade from the electron impact. With correct connection, the electrons fall onto the center electrode, which is a tougher (carbon, platinum or iridium) which survives.
 
I just realized my '82 B2000 had the coil wired backwards. Weird that it would run at all but I put it back to stock and it doesn't run any different...I was hoping that would be the oh **** that was the issue, but its not. Still has a random miss and labors at mandated 650 idle. Only pulling 15 inch vacuum. Vacuum gauge says late timing but that is on the money 8 BTDC.F'n thing could have jumped timing again for all I know. Stupid 4 banger is kicking my ***!
 
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