Voltage Drop?

[gsniegow]

Over the last month or so I have been chasing electrical demons in my '69 Charger (383).  I have made quite a bit of changes to my electrical system as well.  Last night I went to install a voltmeter inside the car so I could keep an eye on the state of things.  I am confused at the number that I am seeing and was hoping you all might be able to point me in the right direction.

Here is a rough illustration of what the electrical system looks like now...

https://lh6.googleusercontent.com/-hFCh4dvG9bo/UAViqpd6U5I/AAAAAAAAGd0/_ooFiMuSgHc/s800/currentwiring.jpg

Taking a voltage measurement going into the bulkhead connection I get 14.x volts.  However, coming out I only see 12.x volts.  So I am dropping a volt or so somewhere.

Changes made thus far:
* Car had the Mopar Performance Electronic Ignition when I got her
* Replaced alternator with a PowerMaster 1-wire internally regulated alternator
*   Disconnected the stock voltage regulator
*   Ran a wire from the alternator to the starter relay
*  Replaced the ignition coil with a MSD Blaster 2 coil
*   Disconnected the ballast resistor and soldered the brown and dark blue wires together
* Bypassed the Ammeter by soldering the black and red wires together
* I bypassed the dimmer switch
* I installed a fuse buss to provide switched ignition current to my accessories that needed it.  Sourced off of the + post on the ignition coil
                  NOTE:  This will be replaced in winter when I rewire the inside of the car, this is temporary
* I installed a new engine wiring harness
* I replaced the battery cables and chasis ground strap

So what confuses me is where does my missing volt(s) go?  I can see taking measurements elsewhere that there are 14.x volts flowing through the system, but for some odd reason I'm only seeing 12.x volts going to the ignition coil???  In looking at the diagram I can't see where the voltage drop is?  I want the voltmeter inside the car to reflect the current state of the electrical system.  Oh, one more note...  As the car accelerates my voltage on the meter bounces around.  Not sure if that matters or not.

Apologies for my ignorance, I'm just out of clues at this point.  As always, thank you in advance!

- Gene

[Big Sugar]

Anything else tied into yor ignition wiring ? Should just have to leeds coming off he coil and possiblr the tach signal wire off the neg terminal on the coil. . Is the car starting nd running ok ?




Ron

[macca3441]

Going by your diagram, the most logical place you getting a voltage drop is in the dash wiring. Check voltage from under dash at bulkhead connector on the Batt +ve wire (Red).
Then, you should check your Batt +ve into your ignition switch (from what used to be your ammeter), then your ignition +ve leaving said switch (brown), then trace the circuit through to bulkhead connector and test ignition +ve there (same brown).
Its just a process of elimination.
Hope this helps,

Wade

[gsniegow]

Ron - Car is running fine, i just want to be able to monitor the electrical system as chasing these electrical demons the last month or so has driven me insane!    As for the coil, I currently have three connections, my third powers my fused electrical bus (which will be redesigned over winter).

Wade - Yeah, that's what I figured as well.  I haven't removed the dash at this point to chase down the drop, but it appears like I'm going to have to.  I was hoping someone would see the diagram and say, "Gene, you idiot, don't forget ___________ drops your voltage!".  I wish those electrical demons had shown their ugly faces over the winter while the car was down for 4 - 5 months! 

Your responses are much appreciated!  Thank you!!

[Back N Black]

That's normal for the coil to have 12 volts. On you stock setup the ballest resistor is by passed during start up and provides 12v to the coil, in the run position the ballest provides around 9.5 volts to the coil. Because you by passed the the ballest resistor you get a constant 12v to the coil.

[gsniegow]

That's normal for the coil to have 12 volts. On you stock setup the ballest resistor is by passed during start up and provides 12v to the coil, in the run position the ballest provides around 9.5 volts to the coil. Because you by passed the the ballest resistor you get a constant 12v to the coil.

I guess I have always believed the statement of the 12 volts going into the ballast resistor was a generalization meaning that whatever voltage was flowing through the system would be sent through the ballast resistor, reduced, and then sent to the coil.  If it is a matter of fact that the stock setup would ALWAYS only ever pass 12 volts, then where in the electrical system is the voltage restricted down to 12?  All I have been able to find in reviewing the wiring diagram is the ammeter (which I bypass) and the ignition switch unless I have overlooked / missed something.

[2Gunz]

The bulkhead connectors offen have problems.

And I would say that's what your issue is.

It looks like you metered the engine side..... But what about Immediatly on the other.


Voltage drops are normally the result of 3 things......

Dirty connections/bad connections.

Amperage draw exceeding wire size

Insufficient source amperage


And keep in mind that some voltage drop should be considered normal.

[gsniegow]

The bulkhead connectors offen have problems.

And I would say that's what your issue is.

It looks like you metered the engine side..... But what about Immediatly on the other.

Correct, I captured measurements at the engine side of the bulkhead.  I have not torn my dashbaord apart at this point, was hoping to delay that to till winter.

Voltage drops are normally the result of 3 things......

Dirty connections/bad connections.

Amperage draw exceeding wire size

Insufficient source amperage

Alternator is putting out roughly 68 AMPS at idle.  When I use my clamp ammeter it showws me pulling roughly 34 AMPS only.  I am going to guess that it is either the bulkhead as you suggest or the dash wires.  Question will be, do I let it go for now and focus on it this winter as planned?  Or do I start ripping it apart now as well. That dash harness wiring kit is quite costly, wow!

And keep in mind that some voltage drop should be considered normal.

That's what I'm trying to figure out.  Should I expect a 1 - 2 volt drop like I am seeing?  I am doubting that I should, but my knowledge in this area is extremely limited.

Thank you!

[macca3441]

You're correct in your assumption......losing 1-2 volts is not acceptable!
As for the ballast only being powered by 12v - that's just a generic term! the ballast will receive whatever voltage is supplied throughout the system.
If the system is being charged at 14v, then (give or take some small droppage) the entire powered system will receive that voltage!
I wouldn't go to the extent of removing your dash to test the electrics...just crawl underneath, and test from there!
Hope this helps,

Wade

[2Gunz]

I believe in the orginal wiring setup it goes from the bulkhead to the AMP gauge.
Try testing it there.


1 or 2 volt's I would say is fine if everything is on.   Headlights, heater, blah blah.

If everything is off I would say you have a problem.

However to really test this you need to find a point directly after the bulkhead in the passenger compartment.
Your diagram shows you only testing area's connected to the ignition system.


As far as now or later......

If it where me I think I would attempt to accerate the problem and go from there.

With the engine off....... and key on.  Turn everything you can on and let it sit for 5 or 10 mins. headlights, heater, wipers, dome light, brake lights, stereo, flashers.........

With the engine off this is going to lower the car voltage.  Lower voltage means more amperage draw.

If you have a problem that needs to be fixed right away its going to show up in the form of blown fuses and/or HOT wires.  (warm is ok)

If it survives that.......  I would move on and just wait.

[Paul G]

I see just a few things I would correct. 

Originally you will have a single (battery pos) wire from the starter relay, through the bulkhead connector, through the ammeter, to the fuse block. Bypassing the ammeter is a good thing since the ammeter is known weak link and fire hazard. The connection this wire makes through the bulkhead connector is guaranteed to be bad. You are losing a volt or two there and making a lot of heat through that bulkhead connection. Take the bulkhead connector apart and you will find that terminal is charred and brown. Drill out that terminal in the bulkhead connector and run a brand new 10 gauge wire right through it. Install a fusible link in that wire where it connects to the starter relay. That is a must. An inline fuse won't do. Behind the dash bypass the ammeter wiring all together and take that new wire directly to the fuse box wiring that used to come from the ammeter. Solder or use a good crimp connector to the existing wire that goes to the fuse box.

Next and most important. Running the alternator output wire to the starter relay is a bad thing. Doing that makes the single wire running from the starter relay to the fuse block carry all the current the car requires, doing it by itself. It has to carry the battery current in to the fuse box as well as the alternator output current to the fuse box. This is overloading that wire which can also cause a fire. Run a new 10 gauge wire through the bulk head connector the same way as the battery wire for this as well. No fusible link in this alternator output wire, it is not needed. Connect to the existing wire at the fuse block that used to go to the alternator.

If you're wiring is old and brittle it won't carry current like it used to. Resistance goes up, voltage goes down, and heat goes up. Make the changes as stated above and retest your voltages.

Read this;
http://www.dodgecharger.com/forum/index.php/topic,74696.0.html

And this; look at the bulk head connector on the fire wall.
http://www.dodgecharger.com/forum/index.php/topic,39153.0.html

[gsniegow]

Some great info - Thank you!!!

It was hot as hell in my garage last night but I poked around some more.  I attempted to take a measurement at the bulkhead as suggested.  With the dash still connected I couldn't access it from the top.  I tried to snake my arms / hands up there but there was no way to do that either.  So I pulled the soldered connection (where the ammeter used to connect) and tested the line there.  On each side of the soldered join I measured 13.6 volts (as was measured going into the bulkhead as well).  So I figured the drop had to be downstream from there.  Only other connection I am aware of is with the ignition switch, so I tried to investigate that.  Another terrible location!  I did notice though that my brown wire appears abnormal.  It looks as if the sheathing around the wire has meltedd slightly.  I'm guessing that this may be the source of my problem.  When I touch the wire its "soft" and doesn't feel right either.  In addition, once I was down there playing all of a sudden the car will no longer start.  So I'm guessing I pulled something or that wire is indeed a problem.  I could not manage to get my about to pass out sweaty arms and hands to figure out how to get a better look so I aborted last night and will look again this weekend. 

Question:  Is there a better / easier way to access the ignition switch electrical?  Can that be pulled forward from the dash?  Or do I really need to hire a contortionist to help me?

PaulG - I have read your posts and I like your approach.  I have a winter project planned to rip out and replace the dash harness.  I like your approach of running clean wires straight through the bulkhead, but I have some questions.  On the battery line, that would still connect to the starter relay, right?  Are you then saying to run a line from the starter relay through a fused link, then through the bulkhead into the car down to the fuse block?  Seems reasonable...  Why a fuse link versus a inline fuse though?  If that link blows while on the road, I better have spares or a good auto club with towing?  With a fuse, I could replace that and be on my way then???  I look at current cars and don't see anything like a fused link, so what advantage is a fused link giving me over a actual fuse?  Apologies for my ignorance, I'm just trying to learn and understand.  Regarding the alternator line, I had planned on running a cable directly from the alternator to the battery.  Is there a problem with that approach?  What is the advantage of running that current through the car and joining at the fuse box?  My understanding was by running it straight to the battery then all of the cars power would come from the line from the battery through the fuse box.  When the car was running the pressure from the alternator would be greater then that of the battery so voltage would flow from the alt, to the battery, to the starter relay, through the fuse link / fuse, through the wire that is run through the bulkhead, down to the fuse block, and then distributed.  My knowledge is limited in electronics but wouldn't that seem like a nice and clean approach?  Thanks again!

[elacruze]

Search the forums for 'bulkhead connector' and you'll find a lot of information on this specific problem and the cures.

Typically the main hot line coming into the car from underhood gets too hot, rusts, melts, and the resistance across the connector goes way up or fails completely. The cure is to run a bypass wire on that circuit.

On a simple electrical wire circuit, a drop of .5v is the absolute max acceptable so you're way over the line for current capacity.

[Paul G]

On the battery line, that would still connect to the starter relay, right?  Are you then saying to run a line from the starter relay through a fused link, then through the bulkhead into the car down to the fuse block?  Seems reasonable...  Why a fuse link versus a inline fuse though? 

Regarding the alternator line, I had planned on running a cable directly from the alternator to the battery.  Is there a problem with that approach?  What is the advantage of running that current through the car and joining at the fuse box? 

Yes the battery line would connect to the starter relay. A fusible link will absorb a momentary over current condition without burning open. A fuse will open whenever current exceeds it's rating. A fuse will put you on the side of the road a lot quicker than a fusible link. That is the reason they used a fusible link rather than a fuse. Modern technology has evolved. We now have slow blow fuses and circuit breakers that reset themselves. Didn't have that in the 60's and 70's.

The circuit is designed to draw current mainly from the alternator with the car running. It can also draw additional current from the battery when needed. Your old amp gauge would tell you when the battery was supplying additional current, or not. Basically a poor set up. It allowed two paths for current flow in to the fuse block. One from the alternator and one from the battery. Two different wires double the current carrying capacity. By running the alternator wire to the starter relay you are forcing all that current to flow in to the fuse block on just one wire, overloading it. 

[Paul G]

If plan to run just one wire to the fuse block it must be a much larger wire like 6 or 8 gauge.