Gen 2 light (again)

[sarge62]

I have been fighting the gen 2 light all day. Thought I had a bad diode trio but it tested good when I pulled the alternator apart. What didn't test good was the rotor windings so i got a new one and put it in along with the new diode trio i already had. The local starter/alternator repair guy actually put it in and he tested it too. Working well but still not charging in the truck. Tested the batteries and they are charged (new red tops) Truck starts fine as long as I keep the rear battery charged. Tested the little red wire on the alt 2 and it had 12.3 volts with the key on and off. The little brown wire had 24v with the key on and nothing with the key off. Took the dash apart and found the gen 2 light was not touching the brass socket because some of the brass had torn off. I got a piece of brass from a old dash board and soldered it in place. got continuity but the light won't come on. Search the schematics (tm-34 p954) and started checking the gen 2 relay. The dash is getting 3.5v at the bulb. Just enough to make it glow like others have talked about. I decided to touch the brown/red -920 wire to ground and the bulb lit up and stayed on till I shut the truck off. Did the same thing to the brown-25z wire. Same thing. But neither time did the alt 2 charge. Tried to clean the alt 2 relay socket but that is tough to do. Any ideas would be great. I'm spent the last 8hrs on this. I tried to attach a diagram but couldn't figure it out.

 

[Corvette1974]

If you are sure that the bulb holders are corrosion free and both working properly (take one and switch it from a known good one), then I'd just rebuild the alternator/s. My gen 2 wasnt charging and I rebuilt both...good thing I did because during the rebuild I checked the rotor from gen 2 and it had open windings. I had to get a parts alternator and take the rotor from that.

Rebuilding the alternators is extremely easy, you just need the kits, simple sockets/tools and a multimeter to test the rotor/stator. Follow the TM guide and the other guides on this site and you can do it. CUCVElectric is where I got my kits from.

Will

 

[sarge62]

thanks will,

I replaced the rotor too because I had a winding that was shorting to ground. I replaced the diode trio too because I had it ordered already. The alt was tested afterward and it charged well. Can I switch the alternators from left to right and see what happens?

The bulbs are good. I found I can get it to light if I ground the brown wire. So the dash is good from the relay up to the bulb.

 

[mistaken1]

thanks will,

Can I switch the alternators from left to right and see what happens?

If the drivers side is an isolated ground unit then yes.

Isolated ground is stock so unless someone changed the drivers side unit to a civilian case ground unit you will be okay.

If you are not sure use your meter to check that the ground terminal is not bonded to the case.

 

[blackhueys]

I had a smiler issues as you. I had both alts rebuilt twice at 2 different shops where I told them i want everything inside tested and replaced if needed. Well I still had the light on. I finally said screw it and opened them up what I found was that not everything was new the internal voltage regulators where factory fro 1986 still I replaced both with brand new American made ones and viola not an issue since. Both alts where showing 12 to 13 volts before but after they were at 13 to 14 volts hope this helps you out as I know it drove me crazy

 

[sarge62]

That is soemthing I thought about. Replacing what is left inside. I this case I can't get the light to come on. If I ground the brown/red wire on the gen 2 relay the gen 2 light will come on. Does that mean I have a bad ground? Where should I look? The relay ground (black wire) is good. If I jump the pink/blk wire to the brown/red wire on the relay the light comes on.

 

[sarge62]

Well, if everything is testing good at the on the truck (brown, red wires at the plug) it must be the alt even it was tested and put out power at the shop. I just ordered the bridge rectifier and the other parts from CUCV Electrics. I will put them in and try again.

 

[mistaken1]

If I jump the pink/blk wire to the brown/red wire on the relay the light comes on.

Right at the relay, what voltages do you read on the brown, brown/red and pink/black wires with the key on and again with the key off? (measure terminal to ground)

 

[sarge62]

wire off on
pnk/blk 0 11.2
brn/red 24.6 24.2
brn/wht 0 0
blkl 0 (good ground)

2 plug alt key off
brn 0
red 12.4 front bat, 24.8 rear bat, 24.8 grd
big red wire key off -12.4 front bat, 24.8 rear bat, 24.8 grd
other post key off -0 front bat, 11.8 rear bat, continuity w/grd

2 plug alt key on
brn 24.8 front bat, 12.0 rear bat, 24.8 grd
red 12.4 front bat, 24.8 rear bat, 24.8 grd
big red wire key on- 12.4 front bat, 24.8 rear bat, 24.8 grd
other post key on- continuity w/grd



The light glows now. The dash gen 2 light was measuring 3.5v. I ordered the CUCV Electric alt rebuild kit because the truck wires are testing good at the alt. So if it is not the truck it must be the alt. I opened that alt up to put I a new diode trio but that was not the problem. The problem was a bad rotor winding so I replaced that and the rebuild I bought the rotor from tested it with the ociliscope and it tested good. So I have seen the alt make power but the light won't come on and The truck wires test good.

 

[sarge62]

wire test numbers

wire off on
pnk/blk 0 11.2
brn/red 24.6 24.2
brn/wht 0 0
blkl 0 (good ground)

2 plug alt key off
brn 0
red 12.4 front bat, 24.8 rear bat, 24.8 grd
big red wire key off -12.4 front bat, 24.8 rear bat, 24.8 grd
other post key off -0 front bat, 11.8 rear bat, continuity w/grd

2 plug alt key on
brn 24.8 front bat, 12.0 rear bat, 24.8 grd
red 12.4 front bat, 24.8 rear bat, 24.8 grd
big red wire key on- 12.4 front bat, 24.8 rear bat, 24.8 grd
other post key on- continuity w/grd



The light glows now. The dash gen 2 light was measuring 3.5v. I ordered the CUCV Electric alt rebuild kit because the truck wires are testing good at the alt. So if it is not the truck it must be the alt. I opened that alt up to put I a new diode trio but that was not the problem. The problem was a bad rotor winding so I replaced that and the rebuild I bought the rotor from tested it with the ociliscope and it tested good. So I have seen the alt make power but the light won't come on and The truck wires test good.

 

[sarge62]

when i said the light glows i meant dimly glows with 3.5v, not brightly as with 24v.

 

[mistaken1]

Shouldn't that brown wire (at the relay) have 24V on it with the key on?

The point is you should see 24V to ground at the gen 2 lamp.

Perhaps your dash circuit board is bad?

 

[sarge62]

So, you think that the brown wire (brn/wht on mine) should have 24v at the relay with the key on. Makes sense coming from the brown wire off the alternator. Which way does the electricity flow? From the alt 2 to the dash relay? Thats what it looks like the way the diode is drawn. I guess that it the possible that I am loosing power through the firewall junction box. I will have to run a wire from the brown alt 2 wire to the relay inside and see if I get any continuity.

 

[mistaken1]

Doesn't the 24V come from the 24V on the fuse panel?

Through the orange wire to the gen 2 lamp on the instrument panel.

Through the lamp then on the brown/red wire to one of the power contacts (not coil contacts) on the gen 2 relay.

Then when the key is on the gen 2 relay is energized so the 24V then travels on the brown wire through the diode, through the firewall connector and on to the terminal on the passenger alternator.

You said you were reading only 3.5V at the gen 2 lamp socket?