Ok here we go again. If I check the voltage at the fuse box I get 10.3 with ignition key on accessory. With off I get 12.4. With the engine running I get 14.2. What could be causing this?
Fred B
Fred B
Low Voltage To Fuse Box
- Thread starter 340Dart
- Start date
-
67Dart273
Well-Known Member
Been many posts on this
Start with the Mad article. Even if / before you do this project, it gives you a simplified diagram of main power in the car and why this happens
http://www.madelectrical.com/electricaltech/amp-gauges.shtml
Follow along on the diagram
The main power originally comes off the starter relay stud and goes through the fuse link, through the BULKHEAD CONNECTOR, to the AMMETER. Through the AMMETER, and to the WELDED SPLICE. This is a splice taped up in the under-dash harness a few inches down from the ammeter black wire. This branches off to feed several things depending on the year of the car, including the HEADLIGHT POWER, the FUSE HOT BUSS, and the IGNITION SWITCH
Additionally, if you are measuring the SWITCHED ACCESSORY BUSS in the fuse panel, it has gone from the SPLICE, through the IGNITION SWITCH and it's CONNECTOR
So in order of some sort of probability, your chances for the bad connection are
bulkhead connector
ignition switch connector
ignition switch
ammeter connections
ammeter itself
in harness welded splice
poor connections right at the fuse panel
or some combination of the above
Start with the Mad article. Even if / before you do this project, it gives you a simplified diagram of main power in the car and why this happens
http://www.madelectrical.com/electricaltech/amp-gauges.shtml
Follow along on the diagram
The main power originally comes off the starter relay stud and goes through the fuse link, through the BULKHEAD CONNECTOR, to the AMMETER. Through the AMMETER, and to the WELDED SPLICE. This is a splice taped up in the under-dash harness a few inches down from the ammeter black wire. This branches off to feed several things depending on the year of the car, including the HEADLIGHT POWER, the FUSE HOT BUSS, and the IGNITION SWITCH
Additionally, if you are measuring the SWITCHED ACCESSORY BUSS in the fuse panel, it has gone from the SPLICE, through the IGNITION SWITCH and it's CONNECTOR
So in order of some sort of probability, your chances for the bad connection are
bulkhead connector
ignition switch connector
ignition switch
ammeter connections
ammeter itself
in harness welded splice
poor connections right at the fuse panel
or some combination of the above
Will check all these. Thanks again.
Fred B
Fred B
iw378
Well-Known Member
340 Dart. If you look in the electrical threads 67dart helped me out a bunch. He even had penciled me up some schematics for ease of understanding. Just look for the post about charging issues
Well I checked and I have over 12 volts every where until I turn the key on. Then it drops to 10.4 volts every where. I already bypassed the bulk connector this year and that didn't cure it. Over 12 volts at the amp gauge until I turn the key on. So could this be my ignition switch? When the car is running it's 14.2 so I'm wondering if it is the switch. I'm not good with electrical.
Fred B
Fred B
67Dart273
Well-Known Member
Read my post concerning the path, post above. You just have to check each point and see where you are losing it, and you MUST check "under load."
To repeat, look at the diagram above. Example:
You turn the key to accessory, and turn on say, the heater blower.
Let's say you check the power going INTO the switch and it's OK, but the feed going OUT to the fuse box is low.
Now what you need to do is probe BOTH sides of the connector, to figure out if the loss is right in the connector or in the switch. Wiggle the connector and see if that changes things.
Another thing you can do is check BOTH the "hot" fuse buss..........the fuses that are hot with the key off AND then check the ones that are hot with key on
If the "hot buss" fuses drop in voltage when the key is switched on, this shows that the load (heater blower) is dragging down ALL of them and that the trouble is most likely NOT in the ignition switch.
The hot buss does not go through the switch. Follow the diagram. It comes in through the bulkhead on the red wire, goes to the ammeter, through the ammeter, out to the "welded splice" and off to the fuse box.
If THAT is low (under load) then it's in
the bulkhead, which you can check
Or the ammeter which you can check
if those two are OK, but low at the fuses, it COULD be the welded splice failed...........and this does and has happened. This is taped up in the black ammeter wire under the dash. Only way to check it is to start at the ammeter and untape the harness a few inches until you find it.
To repeat, look at the diagram above. Example:
You turn the key to accessory, and turn on say, the heater blower.
Let's say you check the power going INTO the switch and it's OK, but the feed going OUT to the fuse box is low.
Now what you need to do is probe BOTH sides of the connector, to figure out if the loss is right in the connector or in the switch. Wiggle the connector and see if that changes things.
Another thing you can do is check BOTH the "hot" fuse buss..........the fuses that are hot with the key off AND then check the ones that are hot with key on
If the "hot buss" fuses drop in voltage when the key is switched on, this shows that the load (heater blower) is dragging down ALL of them and that the trouble is most likely NOT in the ignition switch.
The hot buss does not go through the switch. Follow the diagram. It comes in through the bulkhead on the red wire, goes to the ammeter, through the ammeter, out to the "welded splice" and off to the fuse box.
If THAT is low (under load) then it's in
the bulkhead, which you can check
Or the ammeter which you can check
if those two are OK, but low at the fuses, it COULD be the welded splice failed...........and this does and has happened. This is taped up in the black ammeter wire under the dash. Only way to check it is to start at the ammeter and untape the harness a few inches until you find it.
Ok under load. I will try that. I understand now. Car is in storage so when I get a chance I'll try it again. I really appreciate your help 67Dart273. Sometimes it takes a little hit in the head for me to understand. Thanks again.
Fred B
Fred B
Will do. Thanks.
Fred B
Fred B
iw378
Well-Known Member
I'm leaning towards the welded splice or ignition switch itself. Not sure what kind of voltage drop tests 340cuda has done yet though. Looking forward to hearing back from him. Does he know where to set the voltmeter at and work through the connections systematically.
Luke
Luke
Maybe. I'm thinking since not every fuse is supplied by the ignition switch, some will have 12 volts and other have zero volts before the switch is turned to on. Once turned to on, equal load sharing would result in equal voltage on all fuses whether that is high or low of 12.
Well I checked at all the connections with a load. Had 11.8 at all connections. No drop in voltage at all. The only thing I could figure out is when I moved wires under the dash I must have moved one that was grounding some where. Start the car 14.2 volts every where. With key on no load 12.4 volts. So I have a bad wire some where. Wiggled wires still the same. So I don't know if this will happen again or not. It's got me puzzled.
Fred B
Fred B
64ragtop
Well-Known Member
If the problem went away when you wiggled wires, you DO have a wiring problem and it WILL return at the worst possible time. You need to find where the problem is and fix it.
One way is to remove your instrument cluster and run your hands over every inch of the wiring harness that you can reach while looking at what you're touching. Sometimes a wire has rubbed against something and the insulation gets a flat spot or a small cut, causing a short. Wiggling the wires cleared your short, but eventually the wire will settle back to where it was and the short will be back. Hands and eyes on the wire can find those.
There are lots of sharp edges under the dash, but gloves can make it hard to feel cuts and scrapes in wires. A good head or glasses mounted light helps a lot. When you find the problem repair it properly and secure it firmly.
BC
One way is to remove your instrument cluster and run your hands over every inch of the wiring harness that you can reach while looking at what you're touching. Sometimes a wire has rubbed against something and the insulation gets a flat spot or a small cut, causing a short. Wiggling the wires cleared your short, but eventually the wire will settle back to where it was and the short will be back. Hands and eyes on the wire can find those.
There are lots of sharp edges under the dash, but gloves can make it hard to feel cuts and scrapes in wires. A good head or glasses mounted light helps a lot. When you find the problem repair it properly and secure it firmly.
BC
That's what I'll probably do. Where I have my car stored he really doesn't like you working on it. So I'll have to wait till spring when I take it home. But it does look like I'll have to pull the instrument cluster out.
Fred B
Fred B
-
