Reading wiring diagrams

[1973dust]

On the factory wiring diagrams, are the little arrows that designate connectors oriented in the direction of current flow? On further examination, I think I've answered my own question. It appears they show the male/female side of the connectors? I'm attempting to compare the 73 and 74 schematics. 74, of course, had the dreaded seatbelt interlock system and seems to be significantly more complex. I've recently realized I know just enough to be dangerous about auto electric wiring. When I assembled my car 15ish years ago I blindly plugged a 74 engine harness into the original 73 dash harness. The car has always run fine but I'm showing a 1.5 volt drop in the ignition harness and am wondering if there are things drawing power from the ignition circuit that shouldn't be. On the plus side, my bulkhead connectors look great. No signs of overheating on any terminals. Any advice is greatly appreciated.

 

[67Dart273]

Can you post an example? Of the diagram, I mean

EG if you look at something like the ignition module and ballast terminals, yeh, the arrows would be the pin end of the connector, and the "V" would be the female end of the connector

So far as drop it can be ANYWHERE and more than one place--AND of course is additive. Don't forget the actual switch contacts and the switch connector

One of the biggest drops would be the two circuits for the VR, AKA the ign terminal of the VR itself, and the light blue field lead going to the alternator. Key "in run" and engine stopped, I think it will likely be maximum, tho I have not checked. Of course the ignition module/ coil --if factory also draws current when engine stopped. You can easily pull the connector off the ECU and then one of the alternator field leads to check that

 

[1973dust]

I can post an example this evening. At work right now. I actually got the 74 drawings from you thru a prior thread on here so thank you for that. When I was looking at the schematics yesterday, I did not have the list of circuit designation codes or the pin out drawing for the 74 bulkhead. I found those this morning which should help me tremendously. Am I correct that I can unplug circuits and check for an improvement in the voltage drop to try to isolate the problem area(s)? For instance, the 74 engine harness has extra connectors that the older cars did not have.

 

[Mattax]

1968 Chrysler pamphlet about reading and using the diagrams.
1968 Electrical Wiring (Session 247) from the Master Technician's Service Conference
and the accompanying filmstrip.
1968 Electrical Wiring Filmstrip MTSC (Session 247)

Master Technician Service Conference - Chrysler's Training for Mechanics

For the newer diagrams, see the Nov 1974 Master Tech Book and filmstrip. They are definately a bit more complicated yto follow, but the upside is they show all the connectors seperately.

Browse MTSC by Model Year – 1974 – MyMopar

mymopar.com

 

[1973dust]

Circled in red above is my original question. I know the >> denotes Instrument Connector 5 in this example but does the direction of the arrows mean anything? Is it just showing male/female? I also have circled in yellow 12 Y and 12 BR which, to me, look like they are two wires both connected to terminal ST. However I only get continuity between those 2 wires at the bulkhead when turning the ignition to start. To me, it looks like they are already connected to each other regardless of ignition switch position. This is just something I was looking at trying to verify that I had a clue how to read the schematics.

Next question. Is this showing me that S2 #18 yellow and S1 #18 yellow join together at the bulkhead connector engine side and connect to S1 #14 yellow with tracer dash side. Again, this is just an example to tell me if I'm on the right track.

 

[67Dart273]

The start and IGN2 are a poor *** representation by Ma. NO they are NOT connected. They are on separate switch contacts, to prevent backfeed. They both act the same, AKA are "made" when the key is in start. Yellow energizes the start relay, aand IGN2 bypasses the coil ballast during start

Yes the red you circled should be indicative of the male vs female terminals

 

[67Dart273]

If you have not bypassed the interlock reset box, you need to. This is the device under the hood with the red reset button, on the drivers side fender apron. There will be two yellow ish wires, I think one is yellow, the other yellow/ blk. Connect them together

 

[1973dust]

The start and IGN2 are a poor *** representation by Ma. NO they are NOT connected. They are on separate switch contacts, to prevent backfeed. They both act the same, AKA are "made" when the key is in start. Yellow energizes the start relay, aand IGN2 bypasses the coil ballast during start

Yes the red you circled should be indicative of the male vs female terminals

Okay, that makes me feel better that I'm not just misinterpreting. I'll have to keep in mind that their representation is not always great.

If you have not bypassed the interlock reset box, you need to. This is the device under the hood with the red reset button, on the drivers side fender apron. There will be two yellow ish wires, I think one is yellow, the other yellow/ blk. Connect them together

Thanks, I actually bypassed that several years ago when I was trying to figure out what the reset box even was. I assume that the quality of the connection between those two wires is as suspect as any other? Thanks for the help.

 

[1973dust]

1968 Chrysler pamphlet about reading and using the diagrams.
1968 Electrical Wiring (Session 247) from the Master Technician's Service Conference
and the accompanying filmstrip.
1968 Electrical Wiring Filmstrip MTSC (Session 247)

Master Technician Service Conference - Chrysler's Training for Mechanics

For the newer diagrams, see the Nov 1974 Master Tech Book and filmstrip. They are definately a bit more complicated yto follow, but the upside is they show all the connectors seperately.

http://[URL]https://mymopar.com/browse-mtsc-by-model-year-1974/

[/URL]

Thanks, I believe I looked at a couple of those last night but definitely not all of them and I probably need to look again so more info sinks in. Sometimes this hobby starts feeling like a second job.

 

[Mattax]

Fixed

This diagram is marked to indicate key position, whereas the earlier diagrams with key in dash indicated the terminals on the switch.
ST is start of course
R indicates run
Acc is Accessory position
And the position shown should be marked off.

 

[1973dust]

I've finally got some tinkering time this evening and, thanks to you guys help, I hope I'm on to something. If I check voltage drop to the blue wire after the bulkhead with the 74 engine plug connected I get 1.4-1.5. With engine plug disconnected it's only .2. Does that verify that all connections up to that point are decent and I need to look after the engine connector?

 

[67Dart273]

Measuring voltage with the load disconnected shows you nothing. Voltage drop depends on current through the circuit to show that there is drop. What you want to do is step back through the circuit and check those points as you go along the "path."

You want to do this with all of the circuit properly connected so that the load is "stable." HOWEVER only turn the key to "run" when you are actively making measurements. The coil / ECU will always be drawing current and this can be hard on both if left on for long periods.

I admit this can be a PITA with the new style diagrams in the 73/ later manuals.

The basic path from, "let's say" the ignition system is

The ECU connects to the dark blue "run" circuit at some point, and you can access that right at the ballast resistor. Generally, this goes from there to "maybe" a junction point for the field wire to the alternator and the power to the IGN (blue) terminal of the VR. Then to the bulkhead connector--so check that one, compared to the ballast.

Then you must check the passenger compartment of THAT SAME bulkhead connector cavity, because that IS a connector and there can be drop right there in that pair of terminals. From there back to the proper terminal at the ignition switch, and check both sides of the switch connector. Then check (still at the ign switch connector) the hot power going into the switch ON BOTH sides of that terminal as well. Then you must chase it through the welded splice, the ammeter circuit (if still connected) and then the big red wire going through the bulkhead and to the fuse link.

On the 73 there may be another fuse link/ fuse in that circuit, I do not remember.

I would sit down with your manual, and draw out that part of the circuit, marking EACH terminal/ connector/ switch, etc, in that circuit path

NOW ONE WAY TO ease a work around, unless there are other wiring problems, is to electrically cut the IGN1 "run" wire coming out into the engine bay, and use the firewall end to trigger a relay, hook the engine bay end of the wire to the switched contact, and feed the relay with some say, no12 wire and a fuse/ breaker This will eliminate MOST causes of V drop in these girls, AGAIN as long as there aren't other problems, such as in the engine bay, in that "run" circuit.

 

[1973dust]

I was afraid it wasn't that simple. Please forgive my ignorance, but I'm not understanding how you should have negligible voltage drop with the coil/ECU, choke heater, etc powered up. I guess they're all drawing current but voltage should remain the same? So even though the engine is not running, you basically should still have battery voltage at each location?

 

[Mattax]

Please forgive my ignorance, but I'm not understanding how you should have negligible voltage drop with the coil/ECU, choke heater, etc powered up. I guess they're all drawing current but voltage should remain the same? So even though the engine is not running, you basically should still have battery voltage at each location?

Voltage drops when electrons are trying to move through resistance.
The more electrons trying to get through, the more energy is lost.

But, if the wires are sized large enough there will be no resistance to the normal current those items use.

 

[1973dust]

Voltage drops when electrons are trying to move through resistance.
The more electrons trying to get through, the more energy is lost.

But, if the wires are sized large enough there will be no resistance to the normal current those items use.

As long as all connections are good which is where the problem lies, correct?

 

[Mattax]

Lets try to use your specific situation to further answer the questions.

The car has always run fine but I'm showing a 1.5 volt drop in the ignition harness

Exactly between what two locations is the 1.5 Volt drop measured?
and
Under what scenario was the measurement made?
for example; key in run, engine off, dome light on? engine running after start?
Did you notice what the ammeter indicated at that time? Sometimes thats helpful

blindly plugged a 74 engine harness into the original 73 dash harness.

This may make a little more complicated but basically you have a '73 with 74 engine harness.

 

[Mattax]

As long as all connections are good which is where the problem lies, correct?

Often yes, but sometimes heat, stresses, and oxidation degrade the wires themselves too.

 

[1973dust]

I measured the 1.5 drop between battery positive and alternator field with engine off and key in run. The drop was the same from battery to ballast. I started checking after you guided me thru tightening of the loose alternator output stud. I put the meter on the battery and was charging 16 volts at fast idle which I knew was bad. I tightened up the alternator field connector which helped but I'm still showing 14.8-15 volts charging when warm. No ammeter reading as it is currently bypassed.

 

[1973dust]

I would sit down with your manual, and draw out that part of the circuit, marking EACH terminal/ connector/ switch, etc, in that circuit path

I will do this as soon as I get a chance. That pesky thing known as work is interfering with my car time. I like your relay idea and will probably do that at some point to lessen the load on the ignition switch but I want to learn to track this problem down as per your example first.

 

[Mattax]

No ammeter reading as it is currently bypassed.

Having this disconnected is leaving you blind.
The battery can draw anywhere from 0 to over 40 amps, and knowing how much current its drawing can be really important. I think this will be one of those situation where knowing would be really helpful.
Lets see as we walk through it.

I measured the 1.5 drop between battery positive and alternator field with engine off and key in run. The drop was the same from battery to ballast.

Lets put these on a diagram. I'll leave the ammeter there showing what it normally would show with the key in run, engine off, and assume the door is open so dome light on.

I put the meter on the battery and was charging 16 volts at fast idle which I knew was bad.

OK Yes. This where an ammeter can reveal stuff a voltmeter alone can't.

lets diagram the voltage drop situation you measured.

So we think this represents 1.5 V drop with maybe 7 amps of current.
An amp or so for the dome light, 3-4 amps for the ignition and 2.5 amps for the alternator field.

What I suggest is to check the battery feed next.
That will show if there is resistance between the battery positive and the main splice.

If there is no voltage drop between the batter yand the main splice then the problem is downstream.

(You can increase the load on the battery feed to the main splice if you want to really test its condition. Key off, turn on the lights and step on the brakes. Thats a good 12 to 15 amps. Should still be very little if any resistance)

On the route to the ballast resistor after the mainsplice there is the streering column connector, the ignition switch itself, the connection through the bulkhead, probably an engine connector and maybe an inline splice as shown in the diagram above. That will be a diamond on the '74 shop manual diagram.

 

[Mattax]

What I suggest is to check the battery feed next.

Then normally for troubleshooting I typically check for resistance bewtween the alternator feed and main splice by reversing the setup.

Engine running, battery charged, turn on the lights or some accessories.
Battery charged is so the load isn't changing during the test but more important the voltage drop only will reflect the resistance in the wiring from the alternator to the main splice. The wiring from the main splice to the positive acts as an extension of our test lead.

Hope this helps.

 

[67Dart273]

I was afraid it wasn't that simple. Please forgive my ignorance, but I'm not understanding how you should have negligible voltage drop with the coil/ECU, choke heater, etc powered up. I guess they're all drawing current but voltage should remain the same? So even though the engine is not running, you basically should still have battery voltage at each location?

This is a LOADED question. In a WELL DESIGNED system, there should be almost no drop. This means adequate wire size, adequate terminals, NO corrosion, an adequately designed ignition switch, and no appreciable wear in the switch.

You really have to use your head to decide.

Unfortunately the "run" line drop causes yet another problem and that is, because of low voltage delivered to the VR IGN terminal, this causes OVER voltage at the battery!!!

One way around this problem is to electrically cut the dark blue "run" wire coming out of the bulkhead, BEFORE it is branched off. Take the firewall end of the cut wire, and us that to trigger a Bosch style relay. Feed the relay with about a no12 breaker or fuse protected wire, and connect the engine bay end of the cut "run" wire to the switched contact. This relieves load on the ignition switch, and removes the drop through the bulkhead, as all it is doing is triggering a relay. The key "run" line will still feed stuff like gauges in the pass. compartment, greatly reduced load.

 

[1973dust]

I'm actually working on it right now. Hadn't got out to the garage all week. Your relay fix is exactly what I'm going to end up doing as I've got .3 drop just in the switch itself. I'm at .2 to the welded splice but .5 on blue out of the switch. So far the bulkhead connections have shown almost no drop. I also found a real issue that someone before me had done. The battery buss feed from the welded splice had been disconnected from the fuse block and connected to another wire that was coiled up loose in the dash. They had jumped from accessory to main buss on the fuse block. That explains why I've never had a dome light without the key on.

 

[1973dust]

Update time. I just got done installing the direct charge wire and, more importantly, put a relay on the ignition circuit as described. The drop at the field connection is .4 -.5 volts now which I am going to live with. The turn signals actually flash at full speed idling at night with the headlights on now. I've never owned a vintage Mopar that didn't have the blinkers slow down at idle with the lights on until now. Thanks again to both of you for all of the technical knowledge and advice.