• Hello there guest and Welcome to The #1 Classic Mustang forum!
    To gain full access you must Register. Registration is free and it takes only a few moments to complete.
    Already a member? Login here then!

electrical drain and no interior lights

P

panteramatt

Member
So I finally got my dream car, a 69 mach1. When I got home and tried to unload the car from my trailer I noticed the battery was drained. Put a new battery I had layin around and this one died over night. Whats a good way to narrow down whats causing the drain? My other problem is that no interior light work including the gauge lights.
 
I have a write-up that I give to every harness customer that will answer your question, but it is at home. I'll provide it later tonite!
 
The Idiot's Guide to Short Checking!

Start with the battery disconnected.

When ready to check out the harness, close all doors, turn off all lights, accessories, etc. Then use a digital volt meter to measure the current draw across the battery. First, make sure both battery connectors are disconnected. Connect the positive battery cable to the starter solenoid. Leave the negative terminal disconnected from the battery. Place one probe of the DVM on the negative battery cable terminal, and the other probe on the negative battery post. Be sure that the DVM is set to amps, DC. If there are no shorts in the wiring connections, the reading should be on the order of 30 milliamps or less. Anything above 1 amp indicates some accessory is on; readings above 10 amps (may blow the fuse on the DVM) indicates a dead short.

If you have a short, disconnect all other wiring from the starter solenoid post where the battery connects and re-measure the current. If current drops, the source is the underdash wiring harness or the harness from the starter solenoid to the firewall. Reconnect the wiring to the starter post and then disconnect the underhood harness from the firewall and test again to isolate the source of the short.

If the short is not in the underhood or underdash harness, the problem lies in the alternator or voltage regulator. Disconnect each of these in turn to isolate the source.

If the short is evident in the underdash or underhood harness and you see high current, keep the battery negative side disconnected and remove one fuse at a time. Measure the current as above. If you now see low current, there is either a short or an item on that particular fuse circuit is on. Turn off that item and continue checking.

Eventually, you’ll have low current readings with all fuses installed and all wiring connected. At that time, and only at that time, is it safe to connect the negative battery cable to the battery.
 
Mid-

One side question. I've always checked using the positive terminal. Is there a reason I should use the negative instead?
 
Yes there is! There is a hazard removing the positive terminal prior to the negative terminal if the terminal or the tools used for removal happen to hit the fender apron or other part of the car, which is a ground plane. You'll immediately end up welding things together.

This is simply a safety precaution the guarantees no possibility of shorting if you remove the negative terminal first.
 
Ok this is what I found. I left the neg hooked up and unhooked the pos and checked votage between the post and cable. I had 12.7. I pulled every fuse and nothing changed. I then unhooked the alternator and whatched the voltage slowly drop. So is this the culprit?
 
I believe its the alternator or regulator. I just hooked the battery up and wathced it drain pretty fast. Unplugged the alt from the regulator and watched it come back up. Could it be the regulator?
 
Little more update. The original owner cut and spliced the wires for some reason maybe the bottom plug was messed up. I took the top wire on the plug that goes to the regulator off and the drain is gone. From my manual it looks like it goes to the dash panel. What could be causing this?
 
Without the engine running, and the key in ACC or RUN, the alternator lamp is lit up. The voltage source for this is the VR via the light firewall plug; there is a 15 ohm resistor wire running in parallel with this.

I'm more confused than ever. You stated: I left the neg hooked up and unhooked the pos and checked voltage between the post and cable. I had 12.7. I previously advised you to avoid unhooking the positive, and always make measurements between the negative battery post and the unconnected negative battery cable.

You stated: I took the top wire on the plug that goes to the regulator off and the drain is gone. Was this the plug that goes into the Voltage Regulator? What color was this wire?
 
"panteramatt" said:
Well thats not what this site says: http://1970mgr.org/_BatteryChecks.htm
Click to expand...

The same test is better performed with the negative terminal, and then to use a current meter rather than voltage. Why? You can inadvertently touch ground with your tools or the cable terminal itself while attaching to the battery. That results in over 400 amps of DC current flowing through, enough to weld sheet metal. You cannot do that using the negative battery side. And why measure across the path with voltage? It tells you nothing informative, other than you have a current draw. Measurement with a current meter gives you quantitative information! It's like trying to find a current draw with a lightbulb device versus a true meter. The diagram is incorrect: at rest, the measurement of voltage drain of a good system should be 12.8V.

There are other electrical errors on that site related to conversion of standard to tach harnesses.

Now I can answer your problem. When you disconnected the alternator, you probably interrupted the ground path for all of your systems. Check to ensure you have a good ground path from battery to alternator, from battery to engine block, and from engine block to firewall.

If all is good, please follow my instructions exactly. It will tell you precisely what circuit is causing your current drain, and I can lead you through all of the wiring for that circuit once it is identified.
 
Gatta agree with Mid here- after thinking about the negative post issue, he's absolutely correct. He knows these electrical systems better than anybody, and can walk you through it.
 
Thanx midlife. I definitely know its coming from the top wire. Its orange and was spliced by previous owner. Unspliced it and drain went away. It says in my manual that it goes to the dash panel.
 
"panteramatt" said:
Thanx midlife. I definitely know its coming from the top wire. Its orange and was spliced by previous owner. Unspliced it and drain went away. It says in my manual that it goes to the dash panel.
Click to expand...

Is this wire the top of four or the top of three on the VR plug? What year is your car? The top of three configuration is the Field Relay, and is directly tied to the battery hot side. This wire is typically yellow for early years and orange in later years. If your VR is faulty and has that relay stuck, it can easily suck current from the battery. May I suggest you replace the VR with a new one?

When you say you "unspliced it"...what specifically did you do?

In all of my manuals, the orange or yellow wire ties directly to the battery positive, not to the dash panel.
 
Its on a 69 and it has 4 wires. On my manual its showing it going to the dash panel. I also have NO interior lights at all. The previous owner cut and spliced all the wires coming from the alternator for some reason. All I did was pull the wire apart or unhooked it and the drain stopped. Could the light switch or dash panel be at fault?
 
OK...you have a tach dash, right? That's the only way to have a four wire or contact VR. The top wire is still the F plug for the Field relay, and it should be orange. The next wire down should be white/black. The next wire should be yellow, and the last wire should be violet or green/red. The violet or green/red wire is the only one going to the dash area through the green firewall block. The orange wire goes directly to the alternator via the four prong flat plug and then to the FIELD on the alternator. The white/black wire goes to the alternator as well through the four prong flat plug connector and then to the STAT terminal on the alternator. Finally, the yellow wire goes to the battery (actually the solenoid starter which connects to the battery). Lastly, there is a ground wire connecting the alternator to the VR.

How this all works is this: the violet or green/red wire is the signal for the alternator lamp. There has to be a 15 ohm resistor between the other side of the lamp going to ACC power. There also has to be a 10 ohm resistor wire going from ACC power to the green/red or violet wire at the passenger side of the fuse block. Without either of these resistor wires, the alternator lamp system and the VR may not work correctly. Does the lamp light up with the key in RUN but the engine not running?

I'm going to take a wild guess here, and suspect you have a wiring harness converted from standard (non-tach) to tach, or a mis-match of underhood and underdash wiring. This can give you exactly the problems you are describing of current bleeding from a battery.
 
Actually there is no tach! Is there supposed to be a plug between the alternator and the flat plug that goes to the vr cause there isnt on mine. Maybe it was bad and thats why the previous owner cut and spliced all the wires together. Also, theres like a antennae plug or something below the orange wire that has 2 wires in the same hole.
 
Okay...now we're getting somewhere! Yes, there is supposed to be a short cable between the alternator and the light harness. And yes, the second wire is for your radio suppression device, which can be ignored.

Since your underhood wiring is butchered all to hell and back, I strongly suggest you junk it all and buy nice reproduction wiring, it's good quality at a good price. Otherwise, you'll need to undo all the problems that the previous owners made by unwrapping everything and putting it back together according to how Ford did it.

So...the four wire VR plug is really four wires into three pins? That's for a non-tach system. The Orange wire still goes to the FIELD side of the altenrator; the middle green/red wire goes to the firewall interconnect and ties into the ignition switch and is only hot when the key is in RUN or CRANK (this is the VR exciter), and the green/black wire ties into the battery side of the starter ignition solenoid.
 
You must log in or register to reply here.
Back
Top