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Wiring problems

B

Bill in IL

Well-known Member
Working on a 91 international semi tractor. We have had problems with it charging properly for about the last 10 years. Have gone through and cleaned grounds and connections with no real solution.

Currently have 14.3 volts at the alternator. Positive output terminal of the alternator runs directly to the starter solenoid and then to the batteries among other places as this is used as the central distribution point like many vehicles. When I check the voltage at the solenoid post I get 12.4 or battery voltage. Leads me to suspect bad wire from alternator to solenoid. When I ohm checked that wire it comes back zero ohms. How can this be? I am about ready to change that wire out but afraid I am doing it for nothing. Still thinking its a bad ground somewhere but can't find it.
 
Without the engine running do you have battery voltage on the battery post of the alternator? If so and you still have a voltage drop in the wire, the wire may have been to small for the charging current it carried. This can cause the wire to heat. Over time this can cause the wires resistance to increase. It may not be enough of an increase to measure with an ohm meter but enough to show a voltage drop when charging with a heavy current. Try replacing the wire. What is the current rating of your alternator? If it is upwards of 100 amps or more, a number 12 or 10 wire is NOT heavy enough. You need to replace the wire with some number 4 or 2 cable.

Kent
 
IF YOU HAVE ONE TINY STRAND LEFT IN THE WIRE, OHMS WILL READ ZERO. I WOULD SUSPECT THE WIRE FROM THE ALTERNATOR TO SOLENOID IF YOU ARE CONNECTING THE METER TO THE SAME GROUND.
 
There's a LOT of difference between a wire SHOWING zero resistance with a meter that's putting a few milliamps through it and actually CARRYING 100 Amps.

Run a new wire (of adequate size) and solve the problem.
 
Bill,I had a cranking problem with my 2003 Int'l for awhile until once when starting someone was standing by the door and asked me are sparks supposed to come out down there? upon checking it out I found a 3/8 bolt in a 3/4 hole in the frame, with lots of corrosion. I cleaned it up and put silicone di-electric in there. Made a big difference.
 
Take a voltage measurement across the wire in question and see what it shows with load and no-load on the circuit.
 
That was one thing I thought of after I quit last night to check voltage drop. I don't get to troubleshoot this stuff enough to stay proficient.

Its a heavy maybe 6 or 8 gauge wire running from alternator to solenoid. I have to gather up some good crimp terminals and wire and give it a shot.

All your comments have lead me to belive what I had suspected.
 
you could do a temporary test with one side of a set of jumper cables if the voltage goes to where it should be you know it's in the wire.
 
Disconnect the wire at one or the alternator then see if you can get a test light to work if it doesn't the wire is bad if it does then find out where the bad connection is. It will be somewhere between the the two ends.
Walt
 
Forgot why you use the test light. its because the meter will read voltage at next nothing amps the light will require some amps to work.
Walt
 
I have an old Wheel Horse, which is tiny compared to what you're working on. It had oversized cables, with factory swaged ends. Turns out the ends were not making good connection on the cable. I re-crimped them with my fence crimping tool. Works like new again.

Hope yours is this simple.
Paul
 
WE have two '91 4700 series International bobtails as part of our "fleet" - the electrics gave us fits until we found that the braided ground cables were corroded inside the clip at the frame - they looked clean and tight - once we switched to heavy copper cable for the ground connections our starting problems went away.
 
Will give those another look. We have had starting problems but always attributed them to the alternator problem. The truck is a little tricky to start unless you know its peculiarities.
 
Ohm meter is only checking continunity. You will get a good reading with only one strand of wire good and all the other strands broken. Your best test was the voltage test with the engine runniing. the lower voltage at the solenoid indicates a bad wire between the alternator and the solenoid.
 
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