I'm having electrical trouble with my 73 Charger, only getting 6 volts to the coil...no spark. I know the ECU has to be grounded...but..
When I disconnect the ECU from the firewall, I get 12V to the coil...still no spark. Searched up and down for a short, but no luck.
Brand new motor(it ran before I took it out). Brand new engine wiring harness, ECU, Starter relay, distributor pickup and coil. Still no spark
only other thing I swapped was the stock gauges for rally gauges and under dash wiring, any help would be greatly appreciatde

 

Pulsing on the - side of the coil when you crank it?

 

I did not try that...but I think I've found the problem.... in the dash wiring. After a little persistence, I found voltage in places it should not be and wiring under the dash that did not match the harness in the engine bay....
and the resistor was getting very warm in a short time. Just going to pull the dash wiring and replace it. Thanks for the reply!! Much appreciated!

 

Keep us posted....

 

Well I've changed the dash wiring harness....still the same problem. Checked the negative side of the coil... no pulsing when I crank the motor,
Getting just shy of 7V to the + side of the coil and about 1.5V to the - side...resistor is getting hot.
if I disconnect the brown wire to the resistor I get normal voltage everywhere else.... if I disconnect either of the coil wires I get 12V to both sides,,,
If I disconnect the ECU from the firewall (ground) I get normal voltage...still no spark from the coil. Any ideas?

 

Hum... Should get 12 volt when cranking.
Unplug the ECU and see if you have 12 volts to that.
Make sure the ecu has a good mounting Ground.

 

unplugged the ECU...12.5V from the battery...11.9V at ECU Blue Wire/Yellow Tracer, 11.9V Black wire/yellow Tr, and 11,9V Green wire/Red tr
Note:Green Wire is empty post on ECU.
Both mounting points are down to bare metal...Checked ground with Ohm meter and Volt meter...checked OK
When everything is plugged in, I get 12.5V @ battery, 11.3V @ 3 of the posts on the resistor except for the brown wire which is 6.5V

 

Whats the other side of the resister read when you crank the engine? And also what is the reading at the + post on the Ignition coil when you crank the engine over?
Is it 7 Volts like you said earlier still ?????..

 

. 8.5V at both places...But I'm getting connection from the ground to my blue/yellow ignition wire. I traced it back with an ohmmeter to the voltage limiter on the gauges. It was getting a direct ground to the positive wire. But I think it shorted out my voltage regulator and my ECU....is that possible?.. Both are showing resistance from ground to blue/yellow ignition wire with an ohmmeter. my next step is to buy a new ECU, regulator, voltage limiter... And hope something else isn't shorting all of them out. Ive checked everything I can think of

 

Lets not throw parts at it just yet.. Lets see if we can find the issue...
I thought the Blue/Yellow went to the ignition switch 12 volt run side? Should not go to the VR on the back of the dash? If I read this right...
And 8.0 volts will not let it run...

I'll try to look over some wiring...

 

Correct ....the blue / yellow wire is the hot wire for the ignition run side... But it also runs to the fuse box which powers the instrument panel when you turn the key on

 

Ok. Then unplug the dash wire and see if you now have 12 Volts coming out of the ignition switch to the wire that runs to the resister?

 

I unplugged the dash wire, slightly less than 12 volts at the resistor. So I turned thethe engine over and got spark to the distributor... But it was weak, dumped a little gas in, fired right off for a second then died. Now I have continuity from the ground to the positive battery cable. Tracing back checked all the connections, and when I disconnect the voltage regulator and the ECU both... The continuity goes away. And that's the only thing I can find that affects it. So that tells me the ECU is bad... And voltage regulator is bad... Correct? I'm getting continuity from ground to the ignition run post(blue/yellow) on the ECU also from the ground to the post (blue wire) on the voltage regulator when they are disconnected

 

ok... Put some fuel in the float bowl and lets see if it will run for longer than a second....
I'm not sure I'm with you all the way on what you just said. I'm going to need to think about that for a few..lol
Also, I took the liberty to go hunt down a trouble shooter guide. Please use some of the simple steps. so we might be able to isolate this issue...

http://dave78chieftain.com/Ignition_Syste.html

We can chase the dash wiring issue later.

 

Well....now the engine will barely turn over. I'm getting continuity from the battery to the ground (picture)
When when I disconnect the ECU and the voltage regulator this problem goes away

 

Just wanted to let you know I absolutely appreciate all the time and effort you put into helping me. I've finally found the problem it was the distributor... I've got another one from a buddy... Put it in and it fired right up! Thanks Again!

 

Good Deal, Your welcome on the help side. As you might have been able to tell we would have gotten there at some point. As soo as we got the 12 volts to the coil. and no go we would have been at the ECU and checking the reluctor….
Happy you got it to run.. Now on to the next issue....