PDC

[Daleb]

Well I have finally have the PDC and harness installed in the truck .If you remember the old PDC burnt up at Joint connection 2.I was checking for dead shorts with the pos connected to the battery and using my test light on the neg post of the battery and on the disconnected neg cable.the test light lit so i know there is a short and started to pull fuses.When I pulled the 50amp battery fuse the light dimmed and the next fuse was no change.Pulled the 20amp engine control 2 fuse the light dimmed more. Pulled all the rest of the fuses and the light stayed on but was dim.I am at a loss as to whats going on and am looking for advice.

Thanks

Dale

[Tractorman]

5 hours ago, Daleb said:

Well I have finally have the PDC and harness installed in the truck .If you remember the old PDC burnt up at Joint connection 2.

 

5 hours ago, Daleb said:

I was checking for dead shorts

 

5 hours ago, Daleb said:

I am at a loss as to whats going on and am looking for advice.

 

I do remember that you had trouble with the Joint connection #2 , but don't recall all of the details.  However, many times people associate things like burnt electrical connections, melted solder, etc. to a short to ground somewhere in the electrical system.  This is rarely the case and here is why.

 

Assume an electrical circuit is protected by a 20 amp rated fuse and a short to ground occurs in the circuit.  Instantly an excessive amount of current will flow and the fuse will blow quickly.  No evidence of heat is likely to be found because the occurrence happens very fast.

 

Now let's assume the same circuit has a continuous 10 amps flowing through it and is operating normally.  Pretend that somewhere in that circuit there is a soldered or push-on connector has a poor connection.  Imagine a volt meter connected to both sides of the connector - one side reads 13.5 volts, the other side reads 11.0 volts while 10 amps of current are flowing through the circuit.  This equals a 2.5 volt differential  across the connection while the connection has 10 amps flowing through it. 

 

The result:  2.5 volts (voltage drop) x 10 amps = 25 watts - yes, 25 watts of generated heat at a precise location.  What do you think will happen over time?  Think of it this way - you can buy a 25 watt soldering gun to melt solder at a precise location.

 

In the second example you will note that the current flowing is only half of the rated fuse and the circuit is operating normally with the exception of the poor connection.  A circuit in this status can operate for days or even months without detection until heat does enough damage to break the connection electrically... or start a fire.

 

I don't think you will find a short to ground because I don't think one existed in the first place.

 

- John

 

 

 

 

 

[Mopar1973Man]

Very good explanation... 

[Daleb]

I did a bit more digging today and no matter what I do If the 50amp battery fuse is in the test light is at full bright.when I pull that fuse it dims a bit.I pulled the inline engine connection and the test light went out. I reconnected and the light came on so I pulled the connection on the ecm and the light stayed on so I'm thinking the problem is in the harness between the inline engine connection and the pcm or the harness down to the ecm. Thanks for the replies I can do any job on a vehicle from engine rebuilding to body work but electrical diagnostics is my weak spot and of coarse  that what the problem is.I might be mistaken but looking at the wire diagrams looks like the battery fuse goes to the integrated electronic module. Anyone know where I might find it?

Edited March 30, 2019 by Daleb

[Mopar1973Man]

Be aware that some other devices could be passing power across circuits. What you going to have to do is pull all fuses then one at a time socket a fuse and see what the test light does. This will remove power from all other circuit and allow for full isolation of power per circuit so you can figure out the issue. 

[Daleb]

9 hours ago, Mopar1973Man said:

Be aware that some other devices could be passing power across circuits. What you going to have to do is pull all fuses then one at a time socket a fuse and see what the test light does. This will remove power from all other circuit and allow for full isolation of power per circuit so you can figure out the issue. 

Thanks I never thought about doing that.

[Daleb]

I did some testing with all the fuses in the pdc pulled.still get full power at the 50amp battery fuse no matter what but i think its because its hot all the time please correct me if my thinking is wrong. Next the 20amp engine control 2 fuse has a slight draw. If I unplug the first connector the one closes to the motor of the pcm it goes out none of the others pcm connector make a difference so. Do you think that there is a problem in the pcm? The only other slight draw is from the 40amp abs fuse and it goes out if i unplug the abs pump so something going on there that I will need to look into. Looking for so feed back on what I have found so far.

Thanks

Dale

[Tractorman]

@Daleb, I am not sure of what you are trying to accomplish and I think that you may be chasing your tail here. 

 

Are you still trying to find a short to ground?  I ask because I don't think a short to ground exists.  Are you trying to figure out why joint connector #2 failed due to heat?  If you are, I think I covered that in my previous post - basically,  that a poor connection (in this case, joint connector #2) in a properly operating circuit can cause enough heat to destroy that connection.

 

A test light can be a valuable tool for troubleshooting.  But, if the circuit being tested is not fully understood and / or if the testing tool limitations are not fully understood, then the test results can be useless.

 

Most test lights draw very little current, probably about 250 milliamps on average.  There are control modules on your truck that draw more than 250 milliamps (combined) after the ignition switch is turned off.  These modules will continue to draw power that will easily make a test light glow for a up to a few minutes after the ignition switch is turned off.  Even when the modules finally go to sleep they can still draw up to a combined total of 35 milliamps, enough to make a test light glow dimly. 

 

Different levels of trim on a truck can affect the number of control modules a truck has, as well - for example,  a truck with a security system and a premium sound system will have more control modules than a base model truck (like mine).

 

Electrical problems can be frustrating, but sometimes I get so involved that I can be my own worst enemy.

 

- John

 

Edited April 5, 2019 by Tractorman

[Daleb]

This is what I think caused the melt down a bad g100 ground. Im just trying to cover all my bases before I hook the batteries back up because it was difficult to find a good pdc and don't want to fry this one.

[JAG1]

On 3/30/2019 at 5:18 AM, Mopar1973Man said:

Very good explanation... 

X 2 

 

That should get the tree sap and be a sticky 

 

 

It's just like the other day when my truck wouldn't start because of the cold, I reached under the hood and hooked up the grid heaters without putting the nut in place needed fo make a tight connection.  After starting the truck with the grids I went to pull the ring terminal off the battery clamp. Man that thing was hotter than pistol.

 

I will never do that again.

Edited April 5, 2019 by JAG1

[Tractorman]

2 hours ago, Daleb said:

This is what I think caused the melt down a bad g100 ground. Im just trying to cover all my bases before I hook the batteries back up because it was difficult to find a good pdc and don't want to fry this one.

 

The bad ground is a good find on your part - it definitely needs to be addressed. 

 

Can you expand on why you think this bad ground caused the meltdown in joint connector #2?

 

- John

[Daleb]

One of the heavy equipment mechanics at work said that bad ground could easily put the extra stress on the pdc to cause it to burn up. The day this happened the wipers started to come on by themselves at the time I thought it was a bad switch but that is also a sign of stray voltage from a bad ground. Im hoping thats what caused it because I have found no other explanation that's why I have been paranoid to hook the battery backup and trying to troubleshoot before I do.

Dale

Edited April 7, 2019 by JAG1

[Tractorman]

1 hour ago, Daleb said:

Im hoping thats what caused it because I have found no other explanation thats why I have been paranoid to hook the battery backup and trying to troubleshoot before I do.

 

I understand that you are very concerned that the event won't happen again - I would be concerned, too.  A poor ground at a single connection that combine multiple circuits could cause electrical components to randomly not operate properly.  Heat could build at the poor ground connection, but I don't think it would cause heat to build in joint connector #2. 

 

There could be two ways for heat to build in joint connector #2.

 

  1.  If the connection in joint connector #2 was corroded or cracked, then normal current flowing in that circuit could generate enough heat to damage the connection.

  2.  If higher than normal current was flowing in that circuit, but still less current than the properly rated fuse, then heat could be generated anywhere in the weakest part of the circuit, including joint connector #2.

 

Since there are multiple connections in joint connector #2, you could re-inspect the damaged connector to find out exactly which wires were involved.   Then you would only need to inspect the wiring and components downstream from the damaged connection.  Also, you should make sure nobody has added an additional electrical load to that circuit.

 

- John

 

[Daleb]

1 hour ago, Tractorman said:

 

I understand that you are very concerned that the event won't happen again - I would be concerned, too.  A poor ground at a single connection that combine multiple circuits could cause electrical components to randomly not operate properly.  Heat could build at the poor ground connection, but I don't think it would cause heat to build in joint connector #2. 

 

There could be two ways for heat to build in joint connector #2.

 

  1.  If the connection in joint connector #2 was corroded or cracked, then normal current flowing in that circuit could generate enough heat to damage the connection.

  2.  If higher than normal current was flowing in that circuit, but still less current than the properly rated fuse, then heat could be generated anywhere in the weakest part of the circuit, including joint connector #2.

 

Since there are multiple connections in joint connector #2, you could re-inspect the damaged connector to find out exactly which wires were involved.   Then you would only need to inspect the wiring and components downstream from the damaged connection.  Also, you should make sure nobody has added an additional electrical load to that circuit.

 

- John

 

 

2 minutes ago, Daleb said:

 

 

3 minutes ago, Daleb said:

  1.  If the connection in joint connector #2 was corroded or cracked, then normal current flowing in that circuit could generate enough heat to damage the connection.

This might be it . I remember last summer shortly after I got the truck I was looking into the A/C not working and I pulled the fuse and one side of the fuse was broke and seized in the connector. At that time I remember something drawing my attention to joint connector 2 but I have a bad memory and can't think of what it was. The only other thing that I noticed when I was replacing the wiring harness from the pdc to under the dash is that someone has installed a fuse block thats feeds a solenoid and is powered from the battery. I think someone has made a starter circuit but won't know till the battery is hooked back up to see if I'm right. If they bypassed the starter circuit makes me wonder what happened to make them do that. They left the starter fuse in and the relay so If they have bypassed the pdc stating circuit should they not have removed the fuse and if that is the case guess I should track those wires down and see what they at the end.

Dale

 

 

 

[Daleb]

I looked at the old pdc and the worst melted wire came from fuse 3 eng control 2 and then to the grid heater relay. The relay was in bad shape when I removed it was cracked badly but was still working. Could it have back fed up into the joint connection 2 and caused the damage weather instantly or over time? 

Dale

[JAG1]

You know one cold morning the fuseable links melted on my 12 valve truck. I didn't have enough time to figure out why so after replacing the links I disconnected the grid heaters because thats what I suspected caused it. I never had a problem for years after that running the truck for years without the grids.

 

Daleb, I want to thank you for sharing what you have found so far. Its prompted me to make that ground better on both my 2nd gens. You know..... I think age and gradual deterioration of the electrical system in general can cause a sudden particular problem to show up. Of course I'm not 100% sure on that. So I try to keep my trucks pretty clean in the electrical dept anyway.

 

 

Edited April 6, 2019 by JAG1

[Daleb]

I must say thank you to you all here for your knowledge and patience I really appreciate it.

Dale

[Daleb]

Well hooked the batteries back up. The good news is that joint connection 2 stayed cool the bad is no wait to start light or fuel pump and could not pull any codes so looks like I might have to send my ecm for repair. Lucky these wonderful site has a list of good repair shops.

Dale

[JAG1]

Make sure its not something else before jumping into sending off your ECM.

 

I'm wanting to know..... is you lift pump powered by the batteries and triggered by the factory lift pump connection on a relay? Or is it still hooked up to the factory lift pump connection?

[Daleb]

Im going to check all the connections today because I had the connectors unplugged.

13 hours ago, JAG1 said:

 

 

I'm wanting to know..... is you lift pump powered by the batteries and triggered by the factory lift pump connection on a relay? Or is it still hooked up to the factory lift pump connection?

The lift pump is powered off the battery and uses the original factory connection to turn it on through a relay