Took my car out to top up the fuel for winter storage and was greeted by a dim generator lamp. That's new.

This is the work of others so may have complications? The car has a single-wire alternator installed where the other connections (Blue/Wht.) have been rolled off. The firewall has a newer looking, 4-wire regulator still connected.

The battery voltage is near 13V off and 14.5V when running. Batt. voltage may be read at the alt. wire as in parallel. Looks like it's tied to the horn relay block's positive lug. I disconnected the alt wire and the gen lamp didn't change but of course the batt voltage dropped to 13V. Now the lamp always burns bright when the key is turned on, then goes out on start and comes back dimly within a couple seconds when idling. RPM doesn't affect it.

Okay, after reading about these single wire beasts, I discovered the V-regulator isn't even used. I disconnected the regulator's 4-wire plug and tested her to discover - no change with the lamp behavior. I thought the gen light might remain bright with the reg out of circuit? Nope, seems the reg doesn't play into this. The brown lamp wire on the reg connector was open when testing yet the lamp still came on. What!

So, what is controlling the Gen lamp? I know I can probably just yank the Gen dash lamp but it bugs me something is hiding somewhere controlling it. What else is there besides the reg? It really bugs me that something changed! The lamp used to go out on start so I thought the thing was functional. Now I'm thinking it was a trick not even monitoring the Alt output?

 

Here's a post from Joe_p that might help

"It's no different than on earlier cars. The alternator light circuit doesn't rely on any instrument panel ground. The GEN light has key-switched +12V applied on one side of the lamp. The other side of the lamp is connected to the field terminal on the alternator. When the alternator is not charging, that terminal is grounded in the alternator, causing the light to be on. When the alternator is charging, the terminal also sees +12V (actually, 13.8 in both cases) and the light is off. Now, a dirty or loose connector somewhere in that light wiring can cause a problem, though usually it manifests itself as a dim light.

Now, all of this is moot if the O.P. really is getting less than 13.8V directly out of the alternator."


__________________
Joe Padavano


Then here's a link to the complete thread:

https://classicoldsmobile.com/forums...uestion-2.html

I'm a klutz with electrical stuff, but I hope this helps. John

 

Bad diode trio will cause that also. I found a local alternator shop and got the part for less them $10. Hope that helps.

 

First, a one-wire alternator doesn't connect to the GEN light at all, so unless the two-wire plug was incorrectly connected to the new alternator, any activity from the GEN lamp is meaningless. Pull the bulb and don't look back. My guess is that if the two-wire connector is not plugged into anything, it is probably making a poor ground somewhere, causing the lamp to glow dimly.

Of course, the right answer is to dump the crappy one-wire alternator and get a proper three wire unit like GM and God intended.

Seriously, you can get a 94 amp 12SI as used in the mid-1980s Caddy Fleetwoods with the 307 Olds motor ($93 for a rebuilt AC Delco unit from RockAuto). This bolts directly in place of any GM external regulator or SI-family internal regulator alternator, plugging right in to place (with an adapter harness from NAPA if you're replacing an external unit).

Once again, ask yourself - if GM is trying to save every penny in the manufacture of a new car, why did they never use a one-wire alternator from the factory?

 

Amen!

 

Interesting and thanks to all for the replies!

4-speed455 > yes, a blown rectifier diode will create this issue when used with a conventional Alt but not my 1-wire flavor missing the external reg.

Seems the prior owner stuffed in this 100-150 Amp, chrome special to run his "killer stereo" which has been deleted including his door panel and rear deck butchery. I do intend to upgrade the headlamps to H7 quartz with local relays. They'll create additional load but not crazy stuff here.

To go back to 3-wire, I have a fresh solid-state regulator ready to rock. The two needed wires (with connector) have been taped off at the Alt. harness. Easy swap. I thought the single-wire Alt. was a bonus as internally regulated. I assumed they were more expensive and seem popular with the hotrod crowd, so they must have great magic? Not so much as Joe P. and apparently God points out. The Gen lamp is vintage "cool" where installing a Volt gauge was not my favorite choice. So what's the deal?

Well, after digging a bit, the 3-wire is indeed a better solution. Basically, the "sense" input detects a lower system voltage due to the voltage drop from the sense wire length. Seeing this lower input allows the Alt to produce higher V output which may boost headlamp brightness for example. For the H7 lamps I intend to run, bigger is better. A common complaint with the single wire Alt is lower output voltage and dim lights. However, they are good for farm tractors. Doh!

 

By george, I think he's got it...

 

I have a chrome 100 amp internally regulated alternator. It was advertised as a 1 wire/3 wire. I have it installed with the three wire configuration with an adapter harness on the alternator and a jumper on the regulator harness. That way my idiot light will still work. When my diode trio failed my gen light came on faintly. So if the OP has the same 1 wire/3 wire alternator installed with the adapter the diode trio is probably bad. If the OP truly only has one wire going to the alternator it's probably a bad ground in the gauge.

Now I'm no expert by any means but you got me thinking, should I have any issues with my current configuration? If I swap to a differnt internally regulated 3 wire alternator would that change anything? Thanks.

 

Mine is truly a single-wire flavor. The dim light is a symptom of diode failure but not in my case. The phantom ground is suspicious but I opened the GEN "send" connection to the external regulator and it remained dim. Thus an "idiot" light 'cause I'm an idiot for chasing this!

4speed455, your config. sounds fine as your reg is doing the magic. You have it wired in a conventional manner. If you have the old-school, mechanical firewall mounted regulator, I'd ditch it for a solid-state version. This link was very helpful to understand what's going on here.

http://bob_skelly.home.comcast.net/~...ternator1.html

 

There are different ways to make a 1 wire alternator. The 1wire/3wire will allow for a light function. Other 1 wire designs will not allow the light function. If you have both alternator wires jumped at the reg going to the 2 alt wires, then a 3 wire will work as intended.