Unknown load on electrical system

[MAKG]

Well, I went to Sears, Harbor Freight, Mills Fleet Farm, and a few auto parts stores. Nobody sells a DC ammeter around here, and several employees told me that they didn't exist.

I really don't want to wait a week to get one shipped while my truck sits in the garage "broken".

Back to one of my questions: if there is something drawing that much current, shouldn't it blow a fuse?

Not all circuits are fused. Like the charging circuit. And you could have a short to ground ahead of the fuse block.

No such thing as a DC ammeter? I wonder what I went looking for parasitic drains with.... I might believe no one stocks clamp-on DC ammeters, but none at all?

 

[Evan]

Not all circuits are fused. Like the charging circuit. And you could have a short to ground ahead of the fuse block.

No such thing as a DC ammeter? I wonder what I went looking for parasitic drains with.... I might believe no one stocks clamp-on DC ammeters, but none at all?

Should have clarified, I was looking for clamp-on DC ammeters.

If I had a short to ground on the charging circuit, wouldn't that drain the battery down while the truck is off?

 

[Jspafford]

I hate to disagree, but I would also check your cables.

I had a negative battery cable that was corroded where it was joined to the terminal.

It caused me nothing but headaches. Most of the time it would cause the truck not to start in really inconvient places.

If current has to run thru resistance, it will pull more power.

 

[Evan]

I hate to disagree, but I would also check your cables.

I had a negative battery cable that was corroded where it was joined to the terminal.

It caused me nothing but headaches. Most of the time it would cause the truck not to start in really inconvient places.

If current has to run thru resistance, it will pull more power.

Terminal connections are clean and tight.

 

[Roadkill]

Terminal connections are clean and tight.

The connections themselves on the outside may look that way. Like I said before, I had cables and terminals that looked fine. They had corroded inside and down the cable under the insulation.

You can check for a voltage drop on each cable, if it's more than 0.5V then ditch it. The lower the better, 0.1V is best. Those are large gauge stranded cables and should have a VERY low voltage drop across them since they also are not overly long.

 

[shadetree]

it may still be the charging system (excessive resistance or a blown diode in the rectifier, etc.), or it may be load.

A blown diode in the rectifier??????????? A diode is a rectifier. I think you mean regulator.

Being that there are no other evident problems, I would also suspect the cables, and the battery. Even tho it is new, it could still have problems as it warms up, or is charged. shady

 

[MAKG]

No, I mean the rectifier. It's a bridge, containing 3-6 diodes. If one is blown, a portion of a cycle will get grounded, but the rest won't. It appears on a DC voltmeter to just be lower voltage. You can see that the signal is not properly rectified on a scope. You can also detect it (sometimes) as a significant AC voltage. I've seen charging circuits function (slowly) with one blown diode, but not charge with two.

If the cables are bad, they MAKE VOLTAGE DROPS. If the charging voltage is the same across the alternator as it is across the battery terminals, this is ruled out.

It does not "draw more power." It draws less. It effectively decreases the capacity of both the charging circuit and the battery.

 

[Evan]

I have found the problem.

I started testing around with my multimeter today. I determined the voltage at the battery and the alternator was good, at 14.5v. However my fuel pump was running slow and my voltage gauge in the cab was around 11v. Around this time, the engine died. An attempt to restart failed, and there were limited dash indicator lights coming on and no fuel pump. Since the fuel pump was out I started at the relay. I found there was no power coming from the EEC relay to activate the fuel pump. Power at the EEC relay was about 2.7v. So this brought me to the power distribution box. I tore into the box and discovered MAJOR corrosion. Only 3v coming through the EEC circut, and 10v for fuel. So I gave the box a thorough cleaning and all seems to be well.

I feel a little stupid for thinking this was a parasitic load problem. In reality it was a problem of excessive resistance on the EEC and fuel pump circuits. The volt gauge in the cab must take a reading off the EEC circuit.

Thanks for your help everyone, and sorry for the faulty info...