Universal alternator wiring

[fitterski]

I was getting only 12 system voltage so suspecting a burnt alternator diode I installed a new alternator that was on hand ...to no avail. Seeing that I was unable to finish the TS I thought I should get some advice. The host is a Cat-426 w. a Perkins diesel. One of the alternator connections is "D+" the (309-GY) wire to which on the attached diagram comes form the Start/Run key and passes through a resistor and a diode.

There is NO charge light but there is a completely independent voltmeter. I suspect that the (possibly 2 watt) resistor and diode protect the probably digital innards in the alternator. When system voltage is high enough, juice gets through to BLOCK field power, when the voltage drops it isn't enough to prevent charging so it goes to maybe 14vdc. The thing is that I don't really KNOW that this is so, I'm only guessing.

What would be the next step(s)? Test for a resistor/diode/wire failure by bypassing 12v power through a 2 watt bulb to the D+ terminal and see what it does to charging? If that works then next test just for a resistor failure via the same drill but only across the resistor leaving the diode alone? I don't wanna blow the alternator.

TIA

 

[WranglerX]

The 12 volts through resistor and diode give a quick shot of 12 volts to alternator to initialize alternator to start charge sequence... Lot of vehicles use just small lamp in D+ wiring from "ignition switch" (yeah a diesel) ... Key on (not started) lamp lights (gets ground from alternator) as alternator spins up and puts out 12 volts on D+ terminal and as voltage on D+ matched voltage from IGN switch current (amperage) no longer flows and lamp goes out... Alternator is charging...

Start engine and if lamp stays on, problem in alternator...

Diode in D+ line also prevents run on.. In some vehicle systems out put through D+ is enough to keep ignition coil operating in gas engines (with key off) or possible keep fuel solenoid operated in diesel system. Even with lamp in circuit you "may" need diode...


Dale

 

[fitterski]

The 12 volts through resistor and diode give a quick shot of 12 volts to alternator to initialize alternator to start charge sequence... Lot of vehicles use just small lamp in D+ wiring from "ignition switch" (yeah a diesel) ... Key on (not started) lamp lights (gets ground from alternator) as alternator spins up and puts out 12 volts on D+ terminal and as voltage on D+ matched voltage from IGN switch current (amperage) no longer flows and lamp goes out... Alternator is charging...

Start engine and if amp stays on, problem in alternator...

Diode in D+ line also prevents run on.. In some vehicle systems out put through D+ is enough to keep ignition coil operating in gas engines (with key off) or possible keep fuel solenoid operated in diesel system. Even with lamp in circuit you "may" need diode...


Dale

Thanks very much. The shutoff solenoid power also comes but independently from the key RUN terminal. Still I'm sure that the Cat enginers did not include the diode just to decorate the wiring diagram.

Due to weather it'll probably tomorrow but I will start by checking for voltage from the 'ignition' key downstream toward the alternator with the key ON but engine not running. If necessary the resistance and diode are available in 5-6 days and are not expensive, meanwhile I can operate with just the battery keeping the heating fan on Low

 

[fitterski]

Thanks very much. The shutoff solenoid power also comes but independently from the key RUN terminal. Still I'm sure that the Cat enginers did not include the diode just to decorate the wiring diagram.

Due to weather it'll probably tomorrow but I will start by checking for voltage from the 'ignition' key downstream toward the alternator with the key ON but engine not running. If necessary the resistance and diode are available in 5-6 days and are not expensive, meanwhile I can operate with just the battery keeping the heating fan on Low

SOLVED
The bayonet connector to the resistor was not inserted, saw it as soon as I cracked the instrument cluster open. That's about he 20th line-item that I have to clean up after the machine was in a pro's shop for a month a while back. I don't know what this world is coming to.

 

[WranglerX]

SOLVED
The bayonet connector to the resistor was not inserted, saw it as soon as I cracked the instrument cluster open. That's about he 20th line-item that I have to clean up after the machine was in a pro's shop for a month a while back. I don't know what this world is coming to.

Don't think I could recommend his work to anyone with that may fixes after "pro" was working on it....

Dale

 

[fitterski]

Don't think I could recommend his work to anyone with that may fixes after "pro" was working on it....

Dale

I have two choices within range, one is a chiseler and this other one who's just incompetent ans who used to work for him. Me I'm just an aging DIY'er trying to hang on by my fingernails

 

[PILOON]

I have also seen a few incompetent so called mechanics in the last few years.
If the new generation can't hook up a computer they can't fix squat.
Dealerships with younger clock watching mechanics that only kneel if there is a cushion seems to be today's norm.

Give me an old timer that has grease under his fingernails and a smear or two on his face with dirty coveralls any time.

I have seen parts replaced that were not needed and the dealership had to nerve to want to charge me to re install my proven good parts.
(complaint was a thumping rt rear and they replaced a link @$120. they then wanted another fee to re install my perfectly good link.
( Problem was actually the tail pipe that made contact with the factory installed trailer hitch framing).
LOL, I fixed by clamping a rubber 'bumper' around the frame.

 

[fitterski]

I have also seen a few incompetent so called mechanics in the last few years.
If the new generation can't hook up a computer they can't fix squat.
Dealerships with younger clock watching mechanics that only kneel if there is a cushion seems to be today's norm.

Give me an old timer that has grease under his fingernails and a smear or two on his face with dirty coveralls any time.

I have seen parts replaced that were not needed and the dealership had to nerve to want to charge me to re install my proven good parts.
(complaint was a thumping rt rear and they replaced a link @$120. they then wanted another fee to re install my perfectly good link.
( Problem was actually the tail pipe that made contact with the factory installed trailer hitch framing).
LOL, I fixed by clamping a rubber 'bumper' around the frame.

The new troubleshooting procedure is simple: start swapping out parts somewhere in the suspect system and keep going until the problem disappears, then call all the replaced parts faulty and bill accordingly. I've started applying a new protocol. I don't ask the dealer to fix anything, only to troubleshoot and tell me what's faulty and prove it before billing for the TS service.

 

[fitterski]

RESOLVED Re: Universal alternator wiring

I finally got my 1-wire alternator, had given the wrong alternator body type so had to cannibalize the mounting bracket but it wasn't too big a job. Whadda joy. ONE WIRE TO CONNECT and that's it! (plus the tach lead). Everything works like a charm, like everything that I do attempt though not necessarily right away )))

Thanks for all the pros and cons guys!

 

[ruffdog]

Good to hear it! :thumbsup: