Gen 1 Light Romantic Glow

[Mainsail]

Suddenly I'm noticing the Gen 1 light is glowing softly while the motor is running. Everything else appears normal.

I would estimate the bulb is 35% as bright as it is when I turn the key and the Wait light is on. It goes out completely when I put a high load on the electrical system.

Thoughts?

 

[Curtisje]

Get your alternator tested.

 

[dependable]

Probably a diode going bad. Test w volt meter, should be above 14V when charging, even at idle.

 

[Mainsail]

Telling me where that diode is might save me years of searching randomly around the engine compartment.

 

[Curtisje]

Telling me where that diode is might save me years of searching randomly around the engine compartment.

It's inside the alternator. Test your alternator while the engine is running and like dependable said it should show 14V+. If it shows less it is going bad.

 

[Mainsail]

13.98v on the front battery and 14.77v at the rear.

 

[dependable]

At 13.9, is either under charging, or battery is run down and pulling current. If battery is low, voltage should creep up in a couple of minutes.

Like curtisje said, diode is an internal component of alternator, if you are not into going that far into it, just get it rebuilt (or buy a rebuilt and then rebuild and have a spare). If you replace or have refurbished, make sure vendor knows it should be isloated ground. If they do not know what that is, go somewhere else.

One other thing to check, seems obvious, but still gets me once in a while; make sure belt is not slipping, a lot of times they get thin and look pretty tight, but are worn narrow and slip under load.

 

[Tow4]

The regulator set point is 14.8 volts. If the battery is good, you should read this voltage less than 5 minutes after starting the engine. Battery voltage before you start the engine should be about 12.7.

If the belt is slipping, the pulley will be hot.

 

[TheMountainCalls]

Yeah I'd get your alternator looked at. Had to rebuild mine after a few connections inside melted.

 

[Mainsail]

EDIT to correct:

Gen 1 is making 13.98v

Gen 2 is making just barely under 14.77v

The volt meter rides about 1/3rd in the green, and always has. Since the Gen 1 light, it goes to the high side of green, touches yellow, then corrects back to green when the engine RPM goes up.

With the plug pulled off the (left) alternator the light is out in Run.

 

[Curtisje]

Gen 1 is making 14.77v so it seems counter intuitive that it's going bad when it's rocking the voltage.

Gen 2 is making just barely under 12v but it's been that way for years and not causing any problems.

The volt meter rides about 1/3rd in the green, and always has. Since the Gen 1 light, it goes to the high side of green, touches yellow, then corrects back to green when the engine RPM goes up.

With the plug pulled off the (left) alternator the light is out in Run.

Well I'm confused. Gen1 on both my CUCVs is the drivers side alternator and it powers the front battery. Gen2 is passesnger side and it powers the rear battery. Either you got post #6 backwards or??????

 

[Mainsail]

Well I'm confused. Gen1 on both my CUCVs is the drivers side alternator and it powers the front battery. Gen2 is passesnger side and it powers the rear battery. Either you got post #6 backwards or??????

Oops, yes. Engine running voltage at the front battery (gen1) is 13.98 and the back battery is 14.77.

 

[Curtisje]

I think you need to have Gen1 rebuilt.

 

[Mainsail]

Hit another snag- nobody locally rebuilds alternators anymore.

Is there a reasonable rebuilder I can ship to, or can I just do it myself with a kit?

Wait, since this is the driver's side alternator, it's NOT isolated ground? I can replace with an off the shelf alternator then?

 

[Curtisje]

Hit another snag- nobody locally rebuilds alternators anymore.

Is there a reasonable rebuilder I can ship to, or can I just do it myself with a kit?

Wait, since this is the driver's side alternator, it's NOT isolated ground? I can replace with an off the shelf alternator then?

Yes you can use an off the shelf alternator. Drivers side does not have to be isolated ground.

The website below is the shop in Yucca Valley, CA, that rebuilds my alternators. 2 year warranty. I know they have work shipped to them as well. It may be worth a call.

Premier Power Welder, LLC

premierpowerwelder.com

 

[dependable]

If you are fairly mechanical, it is not hard to "rebuild" them either.

Usually I don't replace the bearings unless they need it, just the diodes, voltage regulator, and sometimes the rectifier. I think forum member Tow4 (in post #8 on this thread) may still sell kits. If not search parts for 100 Amp 27 SI alternator.

Attached is manual for the alternator. The isloated ground is only thing not covered, but is pretty self explanitory if you look inside alt.

 

[Tow4]

I'm not selling rebuild kits anymore but they are available. Search Delco 27SI on your favorite auction site. If you have an original isolated ground unit, don't give it away as a core. They are different from the current production units and can be rebuilt as a spare for the passenger side because they are isolated ground.

There is a link to my rebuild thread in my signature below. It's easy to do.

 

[panama]

I'm not selling rebuild kits anymore but they are available. Search Delco 27SI on your favorite auction site. If you have an original isolated ground unit, don't give it away as a core. They are different from the current production units and can be rebuilt as a spare for the passenger side because they are isolated ground.

There is a link to my rebuild thread in my signature below. It's easy to do.

Ray, how can you tell if you have the original isolated ground unit still?

 

[Tow4]

Ray, how can you tell if you have the original isolated ground unit still?

It will have the insulated ground terminal/post on the back. There are pictures in the rebuild thread in my signature. Non-isolated ground units will have a bolt that screws directly into the case if there is a ground connection.

 

[Mainsail]

I think I read in the stickies that the '75 Cadillac is a good replacement.

The K5 isn't?