Ballast resistor wiring

[halifaxhops]

I have oem diagrams for the model year from MyMopar, but they are points based and then I have tried to find information on how the ECM is typically wired up. You know what they say, " A little bit of knowledge is a dangerous thing" that's pretty much nail on the head for me right now

You whole car is wired like a points car. The electronic was added as per that diagram above is the only difference hopefully.

 

[halifaxhops]

New car to you?

 

[4spdragtop]

Just because the ECU has 5 wires coming out doesn't make it a 5 pin. Remove the boot/cover to chk.

 

[halifaxhops]

Good call Steve

 

[Righty]

Thank you, I'll work through that step at a time. Really appreciate your patience and help.

 

[Righty]

Yeah I will check, I was thinking for a few seconds, well with the jumper off the ignition connection maybe he was just using the extra terminals to connect to but running it as a 2 pin but the coil end doesnt make sense from that point of view as he's got the coil on the 5ohm and the EM on the 0.5ohm. But yep pop the cap and see.

 

[Kendog 170]

There are two wires that come from your ignition you can check. IGN 1 is the blue wire that keeps your car running after cranking. (suspect). Then there is IGN 2 brown wire that is used for cranking on start up.

 

[Righty]

Yes new car to me, I've been tackling a few more mechanical jobs, it's just patience I guess, work through things one at a time and see what the impact is and if in doubt, ask. The FABO knowledge base is pretty vast I reckon.

 

[Righty]

That's helpful, I've been trying to track that from the OEM manual (points based) and the other ECM simplified diagrams I was trying to see how the battery / alternator regulator wires to the coil / resistor ran.

 

[Righty]

So looking at Kens diagram and your comment about the original resistor, would I be correct I wonder in saying the run wire (blue) has been disconnected from the 2 pin resistor and is now running to the 4 pin resistor? I have labelled it as Ignition (Battery) but it's actually ignition run. That is then connecting via the 0.5ohm side to the coil just like a 2 pin resistor would then looking at my photo is it possible he has wired the start wire (in the photo the red wire with white stripe) to the 5 ohm side which because it has a jumper to the 0.5ohm side also connects it to the coil?

I put them together a few years ago and sell them for the printing cost and the ride.

Would you be able to post to the UK or is that too big an ask?

 

[halifaxhops]

Sure just dont know what it cost. I will include a points one also for you. PM on its way

 

[Righty]

Brilliant thanks. That has been a very productive lunch hour!

 

[Mike69cuda]

Just as an fyi, I have a 69 barracuda wiring diagram that has the blue and brown wires reversed. The previous owner gave it to me.

Interestingly enough, he was burning up coils every few months. It took me awhile to figure out that the wiring diagram was wrong.

Mistakes happen on stuff.

 

[Righty]

I'm actually going to take a look through some of the paerwork I got with the car, there's a few print outs in there from old articles with various tuning tips, I think i remeber seeing something on swapping in an ECM unit to a points ignition car, maybe it will give me some tips as to how he did it.

 

[halifaxhops]

Just as an fyi, I have a 69 barracuda wiring diagram that has the blue and brown wires reversed. The previous owner gave it to me.

Interestingly enough, he was burning up coils every few months. It took me awhile to figure out that the wiring diagram was wrong.

Mistakes happen on stuff.

Agree! My 74 dart I could not find a wiring diagram after I had a engine fire. Turned out part of it was in a 75 aspen diagram!

 

[Mattax]

That is probably an old kit. The question is where the person tapped in to power the ECU. In a way it should be easier because they used wire with different colors than factory.

Barracuda wiring diagram is in the the '68 Plymouth Service Manual. I do not know if there was a supplement for RHD cars. Interesting they used a RHD Valient dash. RHD info is illustrated in the assembly drawings but I don't think we needto dig that deep to cover the basics.

Factory scheme for the main circuits; power supplies, main feeds, and ignition.

A is bAttery
R is alteRnator
J1 is Ignition switch feed
J2 is Ignition circuit to run the engine (and alternator field)
J2 is Ignition to start the engine.

A later ECU can be piggy backed onto the original circuits like this

Blue wire to the top of the pentagon connector is power to the ECU.
But the original 1970s ECUs have the additional wire going to a 5 Ohm resistor to help control the current the ECU pulled. That's not shown in the diagram above but you can draw it in.

 

[Mattax]

PDF version of the factory service manual wiring diagrams by one of our forum members

 

[Mattax]

J2 is the original ignition circuit.
J2B is the original segment going to the coil from the .6 ohm ballast.

Oddly we do not see the J2A tied into J2.
Someone may have cut and moved it, or could this be a '69 model year?
In '69 wire J2 goes to the voltage regulator first, and J2A connects from the regulator to the ballaast reisistor.

Also by '69 the neutral safety is combined with the back up light switch in the automatic transmissions.

 

[Kendog 170]

Just as an fyi, I have a 69 barracuda wiring diagram that has the blue and brown wires reversed. The previous owner gave it to me.

Well, You can use a tester to be safe and identify.

 

[Righty]

View attachment 1716414044
J2 is the original ignition circuit.
J2B is the original segment going to the coil from the .6 ohm ballast.

Oddly we do not see the J2A tied into J2.
Someone may have cut and moved it, or could this be a '69 model year?
In '69 wire J2 goes to the voltage regulator first, and J2A connects from the regulator to the ballaast reisistor.

Also by '69 the neutral safety is combined with the back up light switch in the automatic transmissions.

Yes I have the 69 diagram, so I had been trying to translate that to how the ECM was incorporated.
So in my photo would you be saying that J2B and J3 are joined in the connector and still effectively running from the ignition switch to the coil and are still an active part of the start ignition circuit, with power coming from J1 via either R6 or A1A?
And then J2 / J2a (as its a 69 model) is bringing power to the 4 pin resistor and feeding the coil via the red wire labelled coil in my photo? The pale blue wire from the ECM in your illustration corresponds to my dotted yellow wire connecting to J2 but what do you think is the reason for the dotted green wire and also the red wire I marked with a question mark?
Looking at the coil it has 2 wires in to positive - the pinkish wire from the 4 pin resistor that I labelled Coil and another red wire, perhaps this is a continuation of J2B / J3? It's my only explaination, they disappear into a mess ofwires in electrical tape and the red wire comes out of it further along.
The black and yellow wire to the negative on the coil I think does run to the top pin on the ECU as shown in your diagram, there is a second wire (red) from the negative on the coil which I believe might have been to an aftermarket tachometer.

Just saw your little arrow and ? on my photo next to the yellow and black wire, I think this is the wire that goes from the top pin on the ECM cap and runs to the negative on the coil.
.

 

[67Dart273]

If you take the connector off your ECM, does it have 4 pins or 5? If it only has 4 pins, the 5 ohm side is not used and wiring to it is not necessary.

The replacement ballast resistor value is fine.

Dying when you release the key is likely two main causes:

1. Bad ballast resistor.
2. Bad ignition switch.

Could also be loose connections on ignition switch, ballast resistor, or bulkhead connector.

What year / model are you working on? That would help identify wires.

This visual identification is not accurate. Yes, you are right, if you only have 4, then it's a 4. But if it has 5, it still might be a 4. You cannot ID a 4 or 5 pin by sight. One way is to figure out how to remove the 5th wire while running and see if it dies. Another is to ohm out all the pins to each other and ground and see if you can determine if the 5th pin shows any continuity to anything else.

 

[67Dart273]

One way to think about this circuit, is that, other than the ADDED wiring to power the box 12V and the power to the second half of the resistor--which powers just part of the box, is that the run and bypass wiring IS THE SAME as if it had breaker points.

THIS MEANS that regardless of whether you have points or ECU, you should be able to do this:

1...With points, turn the key to run, and be sure the points are CLOSED. With current thus flowing in the coil, measure coil + V to ground. The V should NOT be full 12V but rather quite low, maybe 6--8V. This varies.

WITH ELECTRONIC, this measurement should be about the same. This measurement shows that the "run" circuit through the coil is intact and going through the resistor.

2...With the coil secondary wire grounded, and a meter again from coil + to ground, crank the engine WITH THE KEY and observe the cranking V at coil+. Ideally this should be "same as battery" but likely will be a bit low. It should be at least 11V or more with a good battery. This shows the IGN2/ bypass circuit is correctly wired to the coil.

Observe the "U" cutout on the ceramic resistor block. This was a "key" to the original connectors so that it could not be wired incorrectly. If you look closely at the diagram posted, and orient your resistor as shown, that will guide you as to wire placement.

Notice, EG that the two terminals on the "U" cutout end are jumpered and go to the "run" key circuit.

Also note in the diagram that the IGN2 connection is shown connected to coil +. This will function fine, but physically, is not how the factory was done. The brown IGN2 was always branched in at the coil + wire right at the ballast. The only reason I mention this, is that on an OEM harness, this makes it easy to ID the coil+ wire

Keep in the back of your mind, that you may have a bad terminal in the bulkhead connector, either for the IGN1 or 2, or even a problem in the ignition switch contacts or the switch connector

In an intermittent situation sometimes I recommend running a length of scrap wire temporarily to the affected circuit, and hook that either to a pilot lamp or meter so you can keep your eye on it.

 

[Righty]

Thank you very much, the only circuit testing I have done was rewiring my 50s espresso machine, but I think this is as good a time to start as any. So if I understand what you are describing is ignoring the “5th pin” side of the ballast and focussing on checking the basic start and run circuits and the voltage drop across the low resistance section of the resistor.

 

[67Dart273]

For a start, yes. There are darn few actual 5 pin boxes anymore. If it is an old enough OEM box, it could be. I would be nearly none of the existing, new, or old, aftermarket ECU's are 5 wire.

In the long term, don't discount ANYTHING. I've seen poor connections between the ECU connector and ECU pins, as well as a ratty factory crimp in the ECU connector boot.

If you can round up a .17 cal rifle cleaning brush some of those will fit the ECU, the distributor pickup connector, as well as the VR, and flat trailer connector pins.

Speaking of the distributor, the pickup connector is a "popular" one for an intermittent spark, as there is nearly zero current through that connector. "Work" it repeatedly in/out to scrub the terminals and to "feel" for tightness, and inspect with a bright penlight inside.

 

[Righty]

I think as I said to Halifaxhops, there is a lot of tape wrapped and cable wrapped bundles in the engine bay and it would probably pay me to unbundle these in order to trace the circuits I want to test all the way to the bulkhead connectors etc, as you say don’t discount anything, there could be splices etc I can’t even see. Also perhaps it’s a chance to clean or replace the connectors, certainly the contacts in the ECM looked quite oxidised when I checked them earlier.