1977 D100 225 with double barrel carb.
Battery dead in the mornings.
Disconnected the negative terminal and put a MM between terminal and ground cable.
MM set at 20 A. With Key off 4.75 amp drain.
Remove the near left fuse, Tail Park S/M License, and read 0 A.
The next three fuses to the right are tied together, so the problem is on the near side of the fuse.
So I'm thinking if the key is off and there are no lights on the problem is between the feed side of the lights, and the F47 side of the fuse.
So I think I need to trace the path on the elec diag from the battery positive to see what is next to the line going from the fuse to the license plate light.

Any suggestions? I have done this before but rely heavily on luck.

You probably don't have the same problem but heres the problem I had a couple weeks ago. It was intermittent so it took me a little while to figure out.

http://www.slantsix.org/forum/viewtopic.php?t=39965

Start out simple and set your voltmeter up and start hitting switches (door switches etc) in your car to see if they turn the drain off. If they don't then start digging deeper to find your short.

ESP47: It looks as if you have narrowed the hunt to that branch circuit. Now following a wiring diagram systematically disconnect, or open each sub circuit until the draw goes to zero.

Make a copy of the diagram, fix it to a clip board, and mark off each segment as you test that section, so you don’t over look anything, or test the same branch over and over…

A short can act as a load if it is to a corroded ground. In other words a chafed wire rubbing on a rusted section of frame for example, will act as if it were a low watt light bulb, and not blow a fuse. If the metal surface is substantial enough it will dissipate any excess heat so no smoke show for now anyway. Beware, it is just a matter of time before the fire gods visit with this problem.

For safety, install a battery ground disconnect switch. The one I have been using on my old cars has a green knob, is found at Wal-Mart for about seven bucks. Once the switch is installed, one can disconnect the battery in seconds, without tools, if needed.

_________________
67' Dart GT Convertible; the old Chrysler Corp.
82' LeBaron Convertible; the new Chrysler Corp
07' 300 C AWD; Now by Fiat, the old new Chrysler LLC

I did start to trace the path on the diagram from the fuse back to the tail lights, and it gets really complicated and confusing. So I figured I'd try to trace back to the fuse and got into the same convoluted mess.

So I go out last night and hook up the multimeter again and get the 4.75 amp drain with the fuse in and 0 with it out. I put the fuse in and lay under the truck in the back and find the tail light harness. Everything looks pretty good except the driverside where the wire goes from the frame up into the light housing is real tight, I loosen it up, check the meter and its 0.

That took about 2 minutes. Now I am going to take some plastic armor tubing and put it around the spot that I think is shorting, but...

How did that spot drain the battery? Hypothetically, that sub-circuit bypasses the key switch because the lights will work with the key off. So power goes directly to the fuse and then the light switch and then the tail light. But if the light switch is off, it should not drain the battery. So i checked the diagram again and part of the convoluted path is through the hazard circuit and it looks like there may be some diodes in there.

I don't want to overthink this but would like to know if I found the problem or if it is just a red herring. Any ideas, opinions or criticisms?

You are correct, the running, brake, and directional lights interface with the blinker switch housed behind the steering wheel. Also you are correct, that it gets a bit complicated with all the switches & blinkers, etc. Take your time, one wire at a time, by paying careful attention to color & gage indicated on the diagram, you should be able to trace every thing out. This project may take hours, one never knows, as the fault is always in the last place you look…

You are on the right track looking for chafe points. Another place to look is if the truck has been hit in the past, and you know where the body work was performed, check that area over real closely. Often body guys are not electrically orientated, sometimes a wire gets pinched, and doesn’t show any damage until many ten thousands of miles down the road.

Tracing down a fault often is a tedious irksome task, which will demand a systematic, carefully thought out, plan of attack. Your wire diagram is your friend, don’t be afraid to mark it up as you go along.

_________________
67' Dart GT Convertible; the old Chrysler Corp.
82' LeBaron Convertible; the new Chrysler Corp
07' 300 C AWD; Now by Fiat, the old new Chrysler LLC

Unless you're like me.
Sometimes I find what's causing the problem and not realize it's as simple as just fixing that.
It's safe to assume that Richie is smarter then me!

Electrical problems can require tremendous patience and concentration, and this thread has some of the best advice I've read about logical troubleshooting. Well done!

x2 on using the 'green knob' battery disconnect.
They are extremely useful and well worth the money.

64DartVertible:
Ahh shucks.

_________________
67' Dart GT Convertible; the old Chrysler Corp.
82' LeBaron Convertible; the new Chrysler Corp
07' 300 C AWD; Now by Fiat, the old new Chrysler LLC

Update on this topic: I traced the big parasitic drain to the rear lighting circuit by pulling fuses one by one and looking for improvement. Found the culprit and put some plastic armor around the wires and no more drain.

battery stayed charged but I was still having starter problems. re-ground everything and wam! it starts like a champ now. to be more specific, I identified the main grounds in the starting and charging systems, took them apart, cleaned with electrical cleaner and emery paper, smeared with dielectric grease, and reassembled. I also IDed the main conecters in the circuit and unconnected them, cleaned, smeared and reconnected.

I was looking into an HEI upgrade but found that the stock one is fine. have two spare ballast resistors in the glove box, one came with it and looks like it was the replaced one, one is new from NAPA $8.

I've been running it to work every day and today I had a starting problem and found that I have a 0.8 ohm drain, so I'm leaving the main ground switch off until I can find the culprit.

Lessons learned: GROUND YOUR VEHICLE. I had written this down as one of the first things to do when I got it home from my old motorcycle exploits. did the battery terminals, didn't do the frame and engine cause I didn't have time. DON'T FIX THINGS THAT ARE NOT BROKEN. I had a battery drain and starting circuit problem, why was I looking at HEI? fix what's broke first. ISOLATE THE WIRING IF YOU HAVE A SHORT. I bought enough plastic armor to do most of the exposed wiring but only "fixed" what I had found as the culprit, now I have a new culprit. if you have one shoddy section of wiring that is shorting out, you may have more. plastic armor is cheap, just do it. in looking at the other threads in this forum, most of the people with the answers who show how they did something have plastic clad wiring. there is a reason for this.

Hopefully the truck will start and I'll get home tonight. I'll do the plastic cladding this weekend. Thanks to everyone for the help!

I knew you could figure it out with time and patience...and thanks for the update!

Richie,
If you have conductors leaking kilowatts due to faulty insulation, I would just rewire with correct color & gage wire and be done with it. Running new wire in armor is a good idea.

However armor will not solve a compromised insulation problem. Moisture will continue to enter the conductors creating more corrosion until it over heats and melts, or just brakes off.

Also make sure the lighting fixtures & sockets each have a good ground. Electricity always takes the path of least resistance, so make it easy for those electrons to flow where they are meant to flow…

Good job finding your problem.

_________________
67' Dart GT Convertible; the old Chrysler Corp.
82' LeBaron Convertible; the new Chrysler Corp
07' 300 C AWD; Now by Fiat, the old new Chrysler LLC

Update on the most recent problem: I get home ok and get the MM out to check for drain, still have 0.77 ohm running through when the key is off, sit in the drivers side and lean over to start pulling fuses to see what interupts the flow, the wind blows the door closed on my foot........................DOH!

Lessons learned: DON"T MAKE THE SAME STUPID MISTAKES! People will thing you are an idiot, especially when you post the same stupid mistakes on a website. When you are checking the fusebox for parasitic electrical drain, DO NOT LEAVE THE DOOR OPEN, the dome light will create 0.77 ohms, which will miraculously disappear when you pull the dome light fuse.

I actually would like to rewire the truck but will have to wait for time to do it, probably the winter after next. I rewire all my bikes for simplicity, isolation, and ease of troubleshooting. But I'm not sure if I am the best person to do the rewiring now, with my luck (and stupidity) I'll probably hardwire the dome light on and spend the next several years finding this problem and trying to fix it by closing the door. My next thread:

Dome Light stays on after total rewire - HELP!!!

.77 ohms...............


Do you mean .77 amps?

_________________
Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

Well no, but you make a good point. I'm not the best person to answer this, but I'll take a crack at it anyway.

The current flowing when the dome light is on is more like 18 amps, or the voltage ~13.75 divided by the measured resistance .77 ohms. Give or take. These values don't really matter except that for this fault bigger numbers is bigger problem.

The measured value on a MM for resistance on an open circuit should be infinite. Since it is not really an open circuit on a car, you can usually measure 0 ohms which means that there is some very small resistance in the almost open circuit. You can measure this with a really low setting on a good MM and come up with a value and on modern cars there are acceptable values for this.

So I measured .77 ohms on my not so open dome light circuit with the door open, and said something like theres .77 ohms running through it, which is a false statement, ohms don't run.

What I should have said is, I left the friggin door open again when checking the resistance and i'm an idiot.

What I actually should have said is that there is .77 ohms resistance on a circuit that i am expecting to measure 0 at that MM setting, so I have something with a resistance similar to a dome light bulb in my circuit that I was expecting to be almost open, or 0 ohms.

W/o schematics in front of me, it's hard to say where the problem is very likely to be. A factory FSM or at least the schematics are one of the best investments you can make. Your owners manual probably has a detailed list of what is run by each fuse. Your defroster fan could be on that fuse; it could easily draw >5A.

The headlight switch is in series with the lights, so if the short is there with the switch off either the switch is broken or the short is upstream of that - there are other things on the circuit besides the tail light. There's no point in tracing wiring from the switch to the back if the short is there with the switch off.

4.7A is a lot of current - roughly 56W of heat is going somewhere; you ought to be able to feel that if you can put your finger on it.
If it really draws 4.7A w/o a bright lightbulb somewhere, that's a healthy load. I might suggest you unplug the headlight switch and put the fuse back in to see if the draw goes away, then try the defroster fan. There are very few points not designed for it that will draw that much current for long w/o something melting and/or smoking.

Good luck!

My apologies to emsvitil, I went back and looked at my MM and was measuring 0.77 amps not ohms. So the only truth in what I said was that I am NOT the best person to answer that question.

It turns out that I had a ground problem. The battery was not getting charged and it was hard to start. I re-ground the frame and engine and everything works ok now. I am going to continue disconnecting things and using the electrical cleaner and dielectric grease. The horn wasn't working at all, I took it all apart, cleaned and greased it put it back together and it toots like a champ.

I did have one short in the back with the lighting wires. The left side was pulled tight against the frame. I loosened everything up and the MM shot back to 0. I put plastic armor on that area and made sure it was slack.