Author Topic: Junction box fuseable link keeps blowing  (Read 2044 times)

Offline bd

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Re: Junction box fuseable link keeps blowing
« Reply #15 on: October 04, 2018, 05:12:47 PM »
The brn/wht wire to which you refer is a nickel alloy resistance wire designed to prevent the alternator from attempting to charge the battery through the brown regulator "exciter" lead.  The resistance wire is used on truck models with gauges, only.  Trucks with idiot lights substitute a charge lamp for the resistance wire.  Its purpose is to provide a low current, 12-volt ignition signal to the regulator #1 terminal to turn the regulator on, allowing the alternator to generate charging current.  The current flow through that resistance wire should amount to milliamperes, only.

Unplug the two-wire regulator connector from the side of the alternator and run the engine.  Does the resistance wire continue to overheat?
Rich
It's difficult to know just how much you don't know until you know it.
In other words... if people learn by making mistakes, by now I should know just about everything!!!
87 R10 Silverado Fleetside 355 MPFI 700R4 3.42 Locker (aka Rusty, aka Mater)

Offline Mortyman

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Re: Junction box fuseable link keeps blowing
« Reply #16 on: October 05, 2018, 10:54:50 AM »
While I'm on the hunt for some 24/26 gauge connectors I'll ask this question. With this brown/white resistor wire, I would assume it needs to be a certain length to work properly? I cut out about 12" just to be sure I removed the damaged part when it started melting.

Offline bd

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Re: Junction box fuseable link keeps blowing
« Reply #17 on: October 05, 2018, 11:24:15 AM »
Use an 18-gauge connector and fold the wire over to double its thickness.  Measure the resistance and overall length of the resistance wire that remains intact in the vehicle.  Post the results.


Don't neglect the following step...

Unplug the two-wire regulator connector from the side of the alternator and run the engine.  Does the resistance wire continue to overheat?
Rich
It's difficult to know just how much you don't know until you know it.
In other words... if people learn by making mistakes, by now I should know just about everything!!!
87 R10 Silverado Fleetside 355 MPFI 700R4 3.42 Locker (aka Rusty, aka Mater)

Offline Mortyman

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Re: Junction box fuseable link keeps blowing
« Reply #18 on: October 05, 2018, 04:51:38 PM »
I might have misunderstood your directions and jumped ahead. I spliced in all but the 3 inches of wire that melted. The overall length from steering column connector to the backside of the bulkhead is about 50 inches.  The part where I might have misunderstood was to measure the resistance before I spliced it all back together? I went ahead and unplugged the two-wire regulator connector, started the truck, and it ran without any wires heating up in the cab or in the engine compartment.

Offline bd

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Re: Junction box fuseable link keeps blowing
« Reply #19 on: October 05, 2018, 04:58:21 PM »
Measure the resistance and length of the single strand resistance wire, only.  Exclude any multi-strand wire.
Rich
It's difficult to know just how much you don't know until you know it.
In other words... if people learn by making mistakes, by now I should know just about everything!!!
87 R10 Silverado Fleetside 355 MPFI 700R4 3.42 Locker (aka Rusty, aka Mater)

Offline Mortyman

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Re: Junction box fuseable link keeps blowing
« Reply #20 on: October 06, 2018, 12:36:37 PM »
Removing the wire completely from the harness and any shared connectors, it measures 54 inches long and has a resistance measurement of 0.01 @ the 20k ohm setting or 9.6 @ the 200 ohm setting.
Upon digging into the rear of the bulkhead, this brown/white wire does not share a spot with the 20 gauge brown wire going to the instrument cluster as previously indicated and as shown in a schematic. This truck has gauges and doesn't have that brown wire. The brown/white wire solely goes through the firewall/bulkhead to connect to the 16 gauge brown wire to the side connector of the alternator. And reversely, the brown/white wire goes to the connector on the steering column where it is crimped together in the plug with the 12 gauge orange wire.

Offline bd

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Re: Junction box fuseable link keeps blowing
« Reply #21 on: October 07, 2018, 02:26:54 PM »
The resistance wire is within tolerance, manifesting only a slight deviation from the 10Ω, 6-watt factory specification.  Reconnect all of the wiring.  Connect a DC voltmeter between the battery negative post and the #1 regulator terminal (brown wire), positive voltmeter lead to the regulator terminal.  Start the engine and record the voltage measurement.  Check the resistance wire for overheating.  Post the results.
Rich
It's difficult to know just how much you don't know until you know it.
In other words... if people learn by making mistakes, by now I should know just about everything!!!
87 R10 Silverado Fleetside 355 MPFI 700R4 3.42 Locker (aka Rusty, aka Mater)

Offline Mortyman

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Re: Junction box fuseable link keeps blowing
« Reply #22 on: October 08, 2018, 05:26:31 PM »
Resistance wire did not overheat. No fuseable links have blown. When I probe the back side of the brown wire connector at the alternator I read 15.09 volts.

Offline bd

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Re: Junction box fuseable link keeps blowing
« Reply #23 on: October 08, 2018, 06:15:43 PM »
What are the voltage measurements at the #2 regulator terminal and alternator B+ post relative to the battery negative post?  Then measure the voltage drop between the alternator B+ post and battery positive post, engine running, and the voltage drop between the alternator case and the battery negative post, engine running.  Post the results.
Rich
It's difficult to know just how much you don't know until you know it.
In other words... if people learn by making mistakes, by now I should know just about everything!!!
87 R10 Silverado Fleetside 355 MPFI 700R4 3.42 Locker (aka Rusty, aka Mater)

Offline Mortyman

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Re: Junction box fuseable link keeps blowing
« Reply #24 on: October 08, 2018, 06:57:40 PM »
Voltage measurements at the #2 regulator terminal relative to the negative battery post is 14.7 volts.
Voltage measurements at the alternator B+ post relative to the battery negative post is 14.9 volts.
The voltage drop between the alternator B+ post and battery positive post was .2 volts.
The voltage drop between the alternator case and the battery negative post was zero (both measured 14.7).

Offline bd

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Re: Junction box fuseable link keeps blowing
« Reply #25 on: October 08, 2018, 07:37:18 PM »
The full significance of the voltage measurements isn't really known because the current output of the alternator during those measurements isn't known.  Nonetheless, although there are minor inconsistencies in the measurements, a hard failure is not outwardly evident based on those measurements.  If a charging system issue exists, I suspect it is intermittent.  Place the vehicle back into service and be mindful of any symptoms that may indicate an unresolved problem.

Did you happen to notice where the #2 regulator wire ties into the B+ charge lead?
Rich
It's difficult to know just how much you don't know until you know it.
In other words... if people learn by making mistakes, by now I should know just about everything!!!
87 R10 Silverado Fleetside 355 MPFI 700R4 3.42 Locker (aka Rusty, aka Mater)

Offline Mortyman

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Re: Junction box fuseable link keeps blowing
« Reply #26 on: October 09, 2018, 04:24:39 PM »
This is good news. The #2 regulator wire goes to a spliced 6" fuseable link at the starter. The shared wire from the starter fuseable link goes back to the bulkhead. The b+ charger lead goes to the spliced fuseable link at the junction block. So I'm not sure where they would tie into each other. :-\

Offline bd

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Re: Junction box fuseable link keeps blowing
« Reply #27 on: October 09, 2018, 05:05:57 PM »
The #2 regulator wire is the "voltage sensing" lead used for feedback to the regulator to control alternator output.  In other words, alternator output depends on the voltage that the regulator senses on the #2 wire.  The 12-gauge red wires that pass through the bulkhead connector and the alternator B+ lead connected to the firewall junction block all converge at the starter solenoid 3/8" battery cable stud.  If excessive resistance, such as a loose or burned connection, exists anywhere between the #2 regulator terminal and the alternator B+ post, the regulator will boost alternator output voltage to compensate.  Typically, the voltage that the regulator wants to see on the #2 terminal is in the range of 14.0 - 15.0 volts, with 14.2 - 14.7 volts being the sweet spot.

With this in mind, inspect all wire connections to the 3/8" battery cable stud at the starter solenoid to make sure no wires are loose or appear burned from formerly being loose.  If all appears well then you are probably finished with this particular endeavor.
Rich
It's difficult to know just how much you don't know until you know it.
In other words... if people learn by making mistakes, by now I should know just about everything!!!
87 R10 Silverado Fleetside 355 MPFI 700R4 3.42 Locker (aka Rusty, aka Mater)

Offline Mortyman

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Re: Junction box fuseable link keeps blowing
« Reply #28 on: October 09, 2018, 06:06:06 PM »
This all makes sense to me now. Your explanations are very thorough and easy for a novice like me to understand. You're a great contributor and I thank you very much!

Offline bd

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Re: Junction box fuseable link keeps blowing
« Reply #29 on: October 09, 2018, 06:49:33 PM »
Thank you for the kind words.  You are quite welcome!
Rich
It's difficult to know just how much you don't know until you know it.
In other words... if people learn by making mistakes, by now I should know just about everything!!!
87 R10 Silverado Fleetside 355 MPFI 700R4 3.42 Locker (aka Rusty, aka Mater)