Hi guys,

This past weekend my 1970 Challenger finally pulled it's first "no start" on me (after 5+ trouble free years). I went to fire it up and it just cranked and cranked ..

Checked for fuel and it was fine. Took off the distributor cap and verified the rotor was turning. Checked for spark at the distributor-to-coil wire - nothing. I then swapped out the ballast resistor to a brand new one I had - still no spark.

Finally, I put a multimeter to the coil and checked for voltage with the key both in the "run" position and while cranking - zero voltage both ways.

I know very little about electrical problems, so I'm not sure what to try next? Could the coil or ECU (Mopar Orange) box be bad? Or something earlier upstream like the ignition switch or bulkhead piece? If so, how to test these things?

The car has started so reliably in the past that it surprised me something could have just gone dead without going flakey first, but I guess anything can happen..

Any tips on what to check next would be greatly appreciated!

Thanks much!

first get a wiring diagram,then look at the bulkhead connection.burnt wiring,ballast resistor,fusable links near battery. it should be easy to find.

Try turning the key on and jumping the starter relay on the fender. If it starts then you probally have a bad feed wire from the bulkhead connector.

Thanks guys for the replies.

I did try starting from the starter relay as well - with my remote starter switch -- but still no spark.

Would any of the wires that go through the bulkhead affect only spark while still allowing the starter to crank ? I never quite understood that process..

Thanks!

Could be the ECU took a dump if you have no voltage to the coil out of the orange box. Are you getting voltage too it ? (or just swap the box out real quick if you have a spare around)

Hi, I don't have an extra ECU to try out unfortunately. Is there a way to check the voltage going to the ECU? (I assume it's zero coming out of it since there is nothing at the coil??).

Thanks!

You can check the ballast resistor to make sure you are getting voltage there first off. Then just work your way back to the bulkhead connector. But those orange boxes seem to just take a dump like that


(could be distributor pickup, no voltage through the bulkhead connector,etc,etc.. but ECU is where I would look to first)

Thanks much for the great diagram on that. I will test this out on Saturday when I get over to the car.

To test voltage at the ballast resistor (2-pronged), does it make a difference which way I attach the positive and negative leads on the multimeter? I see that the resistors don't have +/- sides to them ..

Thanks!

take in mind the yellow and red wires ilustrated on this diagrams are slightly incorrect for pre 75/76 cars.

First, yellow wire is really brown and doesn't come from starter relay, comes from ign switch

Second, red wire going to coil is brown OR blue ( depending of year )

the yellow wire coming from starter relay is JUST CORRECT for laters cars where the starter relay provides the ballast bypass instead coming directly from ign switch. Is a very diff starter relay setup

Thanks very much for the info!

If I want to test the wires coming from the bulkhead connector - would I just put the positive prong from the multimeter at the connector on the firewall and ground the negative prong? Or would I need to remove the harness at the bulkhead for this?

Thanks!

You should be able to get your test lead into the end of the bulkhead without removing it.

most likely bad orange box. Check that it didnt lose it's ground. then take off the wire to the coil negative primary terminal and with a jumper wire with an alligator clip on each end, clip one end of the jumper to this coil (pri-) terminal and repeatedly touch the other end alligator clip to ground repeatedly like Morse Code & see if the large coil to dist secondary wire (the dist end) held 1/4" from ground sparks (Check with key "on" and key in "start") If it (large coil wire) sparks (in both positions) that only leaves the dist pickup (not likely) and the orange box (most likely). If it doesn't spark in both positions do Nachos voltage checks to find the open (check/clean the firewall bulkheads 1st) and take all (3) wires (2 small 1 large) off of the coil & w your multimeter see if the pri and sec sides of the coil have continuity. What coil and what ballast are you using?

Thanks very much guys for the crash course in troubleshooting. This really helps! I'll try all this out on Sat.

RapidRobert - My coil looks like it's a stock/oem type - black cylinder 12v. Ballast resistor is a typical looking 2-pronged ceramic one (sorry, don't have access to the car now to see what ohms it is - but I had a brand new ballast spare that I swapped in and it didn't spark with that one either).

Also, I have two wires going to the negative side of the coil (and one to the positive). You said to remove the wire from the "coil negative primary terminal" - which of those two on the negative side might that be?

If I need to detach the bulkhead connector at the firewall to inspect/clean it, does this piece just "snap" out or is there more to it? I've tried never to go near that thing for fear of breaking it..

Thanks again folks for all the tips!

Thanks

I was thinking if you have a high powered coil w a lower ohm ballast that they would be more likely to fail but from your descrip that's not the case here. Take ALL wires off of the coil(-) pri terminal to do the test (your 2nd wire is most likely a tach rpm sensing wire). The bulkheads: some have a wire bail like a master cyl cover & if so take it off or flip it over & you'll see the nubs on the ends of the black bulkhead that hold them on. Depress them inward & wiggle the connector off.

Thanks again Robert! If I need to clean the back of the bulkhead connector unit, is regular electronic parts cleaner spray ok, or are these units too old for chemicals like that?

If your coil has no voltage to the pos. terminal by grounding your multimeter to a good ground not the neg. side of coil you will need to work your way from thier. Your car 70 challenger didn't come out with electronic and scince you said you weren't good at electronics I'm assuming you didn't wire it in. Make sure you have a good ground when you check the coil for voltage by testing the battery positive while using the same ground.

Clean the terminals on the half you pull off w a small bristle brush and the firewall half terminals w an extra seperate male terminal or a small eyeglass screwdriver (be conservative, only need to scrape some fresh brass lines)not open them up any then yes hit it w your spray cleaner.

Thanks very much all for the great tips. I've learned a bunch of great stuff!

I missed that . Yes if the coil positive pri terminal isn't hot in "run and "crank" then as said trace back upstream. I am not grasping why a meter should not be used especially since he has one. Tracing backwards I think he'll find the "open" in a matter of minutes if it is on the eng side of the firewall.

In this situation, there is no voltage when checked with the meter, so continuing with the meter will likely find the fault. You are correct to say that the meter will work

BUT

The reason why a meter isn't always the best tool to find a lack of power for something is simple.

Try this.
Put the negative lead of a voltmeter on to the neg of a battery.
Now put one hand on the positve of the battery, and the other hand on the positive of the meter.

What does the meter read?

Answer: Battery voltage.

You have 12 volts on your hand. Will it run anything electrical?

NO.
The resistance of your body will not allow any current if you try to put a current load across the circuit, Yet you clearly have voltage present on the meter.

If relying on meter readings, you may think the circuit is fine but it's not. An electrical device will not function here.

A meter will find an open( broken wire, etc), but NOT necessarily a high resistance(corrosion in a wire, thermal damage to a connection etc..), without adding a load to the circuit at the same time.
With a test light, the bulb is the load.
If it lights up, you have voltage AND a cicuit that will support a load

In the situation the original poster has put up, there is no voltage, so he will likely find the problem with a meter, if that is the way he goes with it.
BUT
A lot of the time, when "phantom" electrical problems are posted, about things not working, it's a simple error like this, that has caused most of the confusion, and made the diagnosis so difficult. You end up back at a circuit you thought was ok, but really wasn't

Can you help.? Looking at your message when hooking up new ballast resistor No leads on yet. I hook up the
blue wire to the ballast I now have 12 volts at run and the other empty terminal is reading voltage. They say what i've read there should be no voltage on the other leg only at start. I'm lost I have a no start in my 340 cuda orange box.
have power to the coil and power to the orange box. No power going to the dist wires from orange box. Tried a mopar blue box not sure about that no help. new coil no help tried dist no help new ballast no help. I think it has to do with that pick up wires not sure.? Any ideas thanks kevin