Weird charging issue. Have to rev over 3K to show charging.

[Longhorn 70]

I have done a few searches to find this or a similar issue on the board. No luck. So here goes. My truck runs well. It has an alternator with external regulator. The gauge shows it charges fine ONLY if I rev it over 3000 once per driving session. After I shut it off and restart the truck, it doesn't show charging on the ammeter until I go over 3000 RPM. I have checked grounds, the meter, ignition switch, alternator (2 of them), changed the regulator made battery cables out of 00 cable and soldered the ends on and replaced the fusible link. What am I overlooking?

[hayhauler71]

belt tension

put a volt meter on the battery at idle and at 2000 rpm and report back

[LockDoc]

Originally Posted by Longhorn 70

I have done a few searches to find this or a similar issue on the board. No luck. So here goes. My truck runs well. It has an alternator with external regulator. The gauge shows it charges fine ONLY if I rev it over 3000 once per driving session. After I shut it off and restart the truck, it doesn't show charging on the ammeter until I go over 3000 RPM. I have checked grounds, the meter, ignition switch, alternator (2 of them), changed the regulator made battery cables out of 00 cable and soldered the ends on and replaced the fusible link. What am I overlooking?

If you are talking about the stock gauge I don't think you are overlooking anything. They are almost worthless as a gauge. I have two original trucks that the gauges work on and they move very little at any time. Mine may move toward the negative side a small amount while the key is in the start position and positive side a little right after I start it but that is about it. You have to look really close to see it. You might check the 4 amp fuses in each corner of the core support (where the core support and fender meet) to make sure they are good, and not corroded. If they are not there or bad the amp gauge will not work. The fuses are in a small black rubber holder, one on each side...

LockDoc

[dfj73]

Some alternators need to have that rpm to trigger the voltage regulator.

[67 chevelle]

check your wireing to the regulator

[mud.man.rj]

Sounds like the alt is ok, just not the reg, prob the old points style that hang up over time. They can be cleaned and lubed slightly and also have tensioners on a set screw that can be adjusted for when it starts to charge and how much.

[Longhorn 70]

dfi, I didn't know that. Maybe it is an AutoZone alt issue. I have an old one that I can put diodes and brushes in and try.

mud.man the regulator is a new electronic style. I'll try to dig up an old one to at least test with.

I was hoping this was a more common occurrence with a simple solution.

[mud.man.rj]

I have seen more than once the new style reg not work properly with the old style alts. The old point ones worked better than the solid state ones. may have to swap up to an internal reg style alt and ditch the reg.

[VetteVet]

Your problem seems to be in the alternator exciting circuit. It sounds like the exitation wire from the key switch either has no voltage to the regulator or it has too much resistance, more than the 10 ohms required for field exitation.

Pull the plug on the regulator and measure the voltage on the brown wire from the firewall block. you should get 12 volts with the key on and engine not running. If you do then plug it back in and measure the voltage on the white wire that plugs into the back of the alternator, looking for the same reading.
The alternator will excite itself internally with enough RPMS and work fine until the engine is shut off. If it has too much resistance then it will not allow enough voltage to the alternator diode trio for it to charge the fields and turn on the alternator.

The post 6 by Mudman might explain why there is too much resistance in the wire, except that you have changed the regulator. That is why you need to test the voltage on the brown wire before it goes through the regulator.

Lock doc is correct on the gauge so you should take a voltage reading on the alternator
right after startup before revving the engine to see if the alternator is outputting at least 13 volts. if you are getting battery voltage then the alternator is not charging.

Test the battery gauge by turning on the ignition and the headlights, turn signals and the heater fan and look for a large swing to the left on the needle toward discharge. If you get very little then the gauge is suspect especially if the alternator reads 13 volts or more right after engine start.

[Longhorn 70]

Thanks VetteVet. I'll check the brown wire Saturday. That sounds like what's going on. The truck was at a body shop for quite a while and whilst there, someone tried to steal it. They ripped wiring out from under the dash in the attempt. I may not have got it all back correctly. I'll pull out the service manual and double check.

[Longhorn 70]

pfft I couldn't wait until Saturday. I have self-control issues when it comes to Mr. Truck.

I put a meter on the brown wire and tested at the regulator ...NUTHIN. I had 12.8 at the red wire. But 0 on the brown terminal #4! Oddly once I revved it up, I had voltage there. That does lend credence to the self exitation theory.

Can I just run a jumper wire between the red wire on the regulator to the brown wire to test?

I'll have to check the rest of it out on Saturday though. I am going through the wiring diagrams to get a good path to check.

[mud.man.rj]

If I remember right the brown wire runs threw a under dash resistor that can break down, may want to look into that.

[VetteVet]

Originally Posted by Longhorn 70

pfft I couldn't wait until Saturday. I have self-control issues when it comes to Mr. Truck.

I put a meter on the brown wire and tested at the regulator ...NUTHIN. I had 12.8 at the red wire. But 0 on the brown terminal #4! Oddly once I revved it up, I had voltage there. That does lend credence to the self exitation theory.

Can I just run a jumper wire between the red wire on the regulator to the brown wire to test? Yes you can but you should put a 10 ohm resistor in line withe the wire to avoid blowing the diodes in the alternator . That is the purpose of the resistor. Also the red wire is battery power and you can't leave it connected or it will drain the battery when the engine is turned off.


I'll have to check the rest of it out on Saturday though. I am going through the wiring diagrams to get a good path to check.

See below.

Originally Posted by mud.man.rj

If I remember right the brown wire runs threw a under dash resistor that can break down, may want to look into that.

Yes you are correct. The resistor is a brown wire 24 gauge with a white stripe that runs from the key switch down to the inside of the firewall connector, on the opposite side of the brown wire that runs to the voltage regulatror.

The key switch is on top of the diagram and the resistor wire is the 4th wire down. Ignore the arrows they are for another thread.




This diagram shows the resistor wire going from the key switch to the firewall connector.





I'm surprised that no one has suggested that you just convert to the internally regulated alternator and get rid of the pesky regulator. Until you solve the mystery of the exciter wire it won't do you any good to convert, because all the alternators use the brown wire to excite the alternators except the one-wire types.


I am puzzled by why you get nothing on the brown wire with the key on and engine off, yet after you rev the engine then you see 12 volts on it. That explains the alternator action tho. You should see 12 volts as sooon as you turn the key on. The resistor wire is connected to the accessory terminal on the key switch, which is powered as soon as the key is turned on. You might have some resistance in the key switch or a bad wire on the key terminal plug for the brown/white wire, and when the alternator self excites, the extra voltage it supplies would create a connection through the resistance.

[68gmsee]

My problem wasn't having to rev to start charging but I did have a problem with the gauge not showing alternator charging at all.

I later installed several ground straps on my truck and my gauge started working. I believe the ground strap that fixed my problem was the one from the radiator support to the battery negative post. Some components on the radiator support rely on good grounding to work like lights and regulator and maybe the horn but rusty or grime covered bolts don't do it anymore.

[Longhorn 70]

Thanks AGAIN VetteVet!! I'll get this thing yet.

mud.man, I'm betting that wire or its connection is the issue. I had a MESS under the dash when I got the truck back from the body shop. I'll probably have wiring issues the rest of the truck's life.

NOW how do I get 600HP out of my LT4? Just Kidding. I know all I have to do is throw a bunch of money at it.

[Longhorn 70]

I thought this was the wire you were talking about. The 24ga Brown/White.

[mud.man.rj]

Just run a new keyed wire in place of the brown wire.

[VetteVet]

Originally Posted by mud.man.rj

Just run a new keyed wire in place of the brown wire.

Yes you could do that and I almost suggested it, but you still need the resistor inline, and I like to stay with the stock setup because it is easier to see in the diagrams I post, and for all the people who read these threads to follow.

[mud.man.rj]

Could add a Chrysler style or Gm ballast resistor, but really overall is still a cr@ppy old system at it's best, would have just added a newer style internal reg alt and put the old non trust worthy alt and reg in the past, all the extra wires and plugs, why.

[GuyO]

Longhorn, just a FYI - you can take whatever VetteVet says to the bank. We are very lucky to have him here. Something to consider, I found I had a break in the wire from my alternator and it would behave sometimes and not charge other times, even over charge at times and burn the fusible link/maxi fuse. I ran all new to the voltage regulator. Good luck with it, we are watching and got our fingers crossed for you. G.

[68K30]

My 68 did the same thing years ago and I converted it to an internal regulator unit. A couple years ago I had the ignition switch out and found the brown wire with the white stripe was real loose in the crimp at the switch, same symptom no voltage at the brown/white wire under the hood. I soldered the wire to the terminal and that fixed it.

[Longhorn 70]

Done! Fixed! Charging from start. Thank you VetteVet. The 24 awg brown/white wire was not connected where it should have been. When I rewired the plug, after they tried to steal the truck, I didn't connect the br/whi to the ignition switch connector. I had a few extra of the connector inserts.

Cut the one going to the brown wires off.
Strip the 3 wires I cut off.
Add the brown/white to the group.
Crimp.
Push back in to the connector shell.
Install the plug/switch.

Start truck and watch it charge.

Now it starts charging right off the bat as well as shows discharge whilst trying to start the truck.

Thank you ALL again for the help.

[pjmoreland]

My truck is having the same issue where I have to rev the engine to get the alternator to start charging. My brown/white wire has good connectivity from the ignition switch to the voltage regulator. With the key in "run" position and the voltage regulator connector unplugged, I am measuring 12V on the brown wire at the voltage regulator. I also measured the resistance of the brown/white wire from the ignition switch to the voltage regulator when unplugged and it is about 13 Ohms. This is higher than the 10 Ohms VetteVet mentioned up in post #9. I am wondering if this is because my harness was originally an idiot light harness that I converted to gauges. This could make a difference because there is no longer a Generator indicator light running parallel to the brown/white wire which would have increased the voltage to pin 4 of the voltage regulator a bit. I no longer have the indicator light connected to the brown/white wire at the firewall bulkhead connector.

I was looking through the factory service manual schematics and noticed the brown/white wire appears to be teed in mid-way along the brown wire that runs from the ignition switch to the fuse panel on the C/K10-30 schematic with gauges. This would shorten the brown/white wire, which would reduce its resistance and account for the absence of the extra current that would be provided by an idiot light. The idiot light schematic shows the brown/white wire going all the way to the ignition switch. Do I need to cut my brown/white wire from the ignition switch, shorten it, and reconnect it to the 12-guage brown wire closer to the fuse panel? Can anyone who has a truck that came stock with full gauges comment on whether the brown/white wire is connected directly at the ignition switch or not?

[pjmoreland]

I hooked a 194 bulb up to the brown wire at the voltage regulator, and connected the other end of the bulb to 12V. It lights up when the key is in the "run" position with the engine off. When I start the engine, the bulb stays lit up. When I rev the engine, which causes the alternator to start working, the bulb turns off. It seems that the extra voltage from having the bulb connected doesn't solve the problem.

When the engine is running but hasn't been revved yet, I've got 0.6V on the white wire and 11.7V on the blue wire at the alternator (they change to 14.8V on white and 8V on blue after revving). If I'm reading the internal schematic of the voltage regulator correctly, the white wire is supposed to use voltage generated by the alternator (isolated from the battery voltage by a diode) to activate the field relay in the voltage regulator. Is my alternator bad?

[gmc684x4]

One of the many reasons I upgraded to a 10si alt 3 decades ago and upgrading again to a cs144