M1009 charging issues

[GunnyM1009]

Alright i've been through what i can find in the TMs and the sticky. Gen 1 I have 12.7v on red wire and 0 on brown key off 12.7 on brown key on and 12.7 on front battery running or not. Gen2 I have 25v on red 14 on brown key off. Same with key on and 12.8 on rear battery. Running or not. Now with truck not running on positive post for gen1 I have 12.7 on gen2 I have 25. Running I have 24 on gen 1 and 25 on gen2 but the batteries reading stays the same. Any help would be appreciated.

 

[tim292stro]

Double check your numbers on the Gen1 running voltage, I presume an error there.

For the Gen2 voltages, measure from the alternator's ground lug to the terminals, not the chassis ground and it'll give you what would appear to be normal 12V voltages on your readings - it's best to think of the upper 12V charging system and battery as a separate 12V system.

With the engine off, remove the two wire terminal from the alternator and measure and report the voltages on the two wires (red, brown skinny wires) to the same alternators ground wire (fat wire). Turn the key on but do not start, and measure/report the voltages again. Final question - have you checked your idiot lamps? Do they turn on when you first turn on the key?

 

[GunnyM1009]

Gen 1 running is accurate. Just double checked measuring from ground lug and positive lug on alternator. Gen 2 is measuring 12.7 and 12.7 on both terminals and I just noticed while running my gen 1 light stays dimly lit

 

[tim292stro]

Sounds like your voltage regulator is going on gen2 at least - the idiot lights are attached to to field coil (what makes the alternator generate power), if the light is turning on that means the field coil is not being powered.

Can you clarify this from your first post?

...Running I have 24 on gen 1 and 25 on gen2 but the batteries reading stays the same...

That part about 24 on Gen1 is very confusing and/or concerning.

In general I'd expect:

Low-side battery:
Engine off: ~12.7V
Engine on: ~14.4V

High-side battery:
Engine off: 12.7V (25.4V from chassis ground)
Engine on: 14.8V (28.8V from chassis ground)

All of the voltages for red wires to a given alternator should follow the battery attached to that alternator (Gen1 follows front/low-side battery, Gen2 follows rear/high-side battery). If the alternators are not generating power, the battery voltages will never get above the voltage they show when the truck is not running (they don't generate power they just store power). So if your low-side battery is not getting over 13V while the engine is running, it's not charging either.

One thing to be sure of, is to get your engine over 1200RPM, your alternator may not actually start charging until it sees high enough RPMs to start doing work.

 

[GunnyM1009]

Both alts tested fine at a reputable auto electrical shop.

 

[tim292stro]

Next step then is to check your fusible links and the other idiot light. Are the idiot lights turning on solid when you turn the key before you start the truck?

 

[GunnyM1009]

Gen1 does gen2 does not. What other fusible links are there other than the 4 on the terminal block and the 1 on gen 2

 

[GunnyM1009]

The fuse and relay for gen2 are good and I just replace the pcb for the instrument cluster

 

[tim292stro]

If you pull the cluster you are going to need to measure the terminals for the gen 2 idiot light.

When the ignition is switched on one of the two terminals should be reading ~24V to chassis ground. If not, your 24 fuse is bad. It's important to note that the idiot light circuit is part of the alternator's exciter supply - if no power is provided to the idiot light, the bulb is bad, or any wiring between the idiot light and the alternator is bad, the alternator will not start charging.

You having just touched the PCB on the cluster makes me suspicious that there may be something going on there. All it takes is bad connector contact or a bad socket and the alternator won't work.

 

[GunnyM1009]

No voltage to the socket. Quick note the reason I replaced the pcb is because gen1 light didn't work. Now after replacing it all lights works except the gen2 light

 

[GunnyM1009]

Also the charging system wasnt working prior to pcb replacement

 

[tim292stro]

Work your way back from the socket - that bulb is powered by the 24V relay. Check the connection to the PCB from the harness and double check that wire is good from the relay.

 

[Warthog]

Where did you get the new circuit board from? Did you compare each circuit to your old one? Just thinking you may not have the correct one.

There are two types of clusters. One with idiot lights and one with gauges. They may have sent you the wrong one.

Also I removed HELP from the title. We like to reserve that for when you are broke down on the side of the road.

 

[GunnyM1009]

The pcb came from classic industries and yes the circuit ribbon matches exact. It is the one for the idiot lights. Im stumped to say the least ive had the power probe and multi meter out all day and I am more confused than when I started

 

[GunnyM1009]

Also compared part numbers on the pcb before installation

 

[GunnyM1009]

Checked the four fusible links on the distribution block and the one on gen2 all are good. All the fuses are getting power at both sides

 

[tim292stro]

One more check you can do is to short the brown wire to the alternator's ground and see if the idiot light turns on when the key is on. If they don't, then your circuit is bad somewhere and you need to check again.

If the fuses/links are good, the bulbs and connections are good and the voltages are correct at all of the terminals - there is only one likely truth left: the alternators are in fact bad.

 

[GunnyM1009]

Thanks I will go through everything again over the next couple of days I had to go ahead and stop for today. I am at the point of throwing stuff and am just feel like I am being repetitive. I will begin again with a fresh mind and methodical process after work tomorrow. If anyone else has any ideas feel free to post them and I will start through the list tomorrow.

 

[GunnyM1009]

Something i did notice last thing is that on gen1 with the exciter wire unplugged im getting 12.7 volts but with it plugged up I only get 4.6both readings are on the exciter wire with the key on not running. Any idea why that is.

 

[tim292stro]

That's the current hopefully going through the idiot light while the field coil is not being driven - the light should be on in that condition.