Low voltage to both exciter wires

[MTMUDRUNNER]

I have been searching through old posts and have come up with a few answers that might be right. Here is my situation

Gen 1 light comes on when I turn the key on and after started it dims a little, when I am driving and the rpms are higher it dims to the point you cant see it in the day time. If I turn the heater on the light gets even dimmer yet. This has been happening for a long time and I can't seem to figure out what is causing it, this is what I have checked

Gen 1
key off red wire 12.8V
Key on brn wire 9.47v
Running large red wire 14.12v

Gen 2
key off red wire 25.5v
key on brn wire 14.3v
Running large red wire 29.0v

Battery 1
idol 14.42v
high rpms 15.4v

Battery 2
idol 14.63
high rpms 14.65

24v check
idol 29v
high rpms 30.1v

 

[markg]

I have been searching through old posts and have come up with a few answers that might be right. Here is my situation

Gen 1 light comes on when I turn the key on and after started it dims a little, when I am driving and the rpms are higher it dims to the point you cant see it in the day time. If I turn the heater on the light gets even dimmer yet. This has been happening for a long time and I can't seem to figure out what is causing it, this is what I have checked

Gen 1
key off red wire 12.8V
Key on brn wire 9.47v
Running large red wire 14.12v

Gen 2
key off red wire 25.5v
key on brn wire 14.3v
Running large red wire 29.0v

Battery 1
idol 14.42v
high rpms 15.4v

Battery 2
idol 14.63
high rpms 14.65

24v check
idol 29v
high rpms 30.1v

generator one regulator is bad, overcharging.

 

[scottladdy]

Gen 1 circuit is shared with the blower circuit. Something else to consider is replacing the blower motor, switch, and resistor mounted on the firewall. Clean your contacts while you are at it. If you shop well, it is less than $50 for all 3 parts and, like the headlight circuit harness upgrade, should save you hours of issues down the road. While you are in there, check the "ribbon" cable for shorts, especially where it passes through the firewall.

 

[Warthog]

Have you ever taken the firewall plug apart? Sometimes a low voltage situation occurs because of dirty contacts with the plug.

From the engine side unscrew the center bolt and pull the plug apart. Use some Electrical Contact Cleaner and an old tootbrush and go to town cleaning both parts.

GM used some type of grease (I don't know what it is) on the plug and over the years between the heat, oxidation and dirt, the grease has turned into a black goo.

I have seen on more than one occasion the GEN1 issues have been because of the dirty firewall plug.

Of course YMMV.

 

[doghead]

I always suggest rebuilding the alts, on a new to you CUCV.

 

[markg]

for my 1028 you see to the left, gen 1 light was not working, ended up being the bulb socket , easy to reach laying on your back. pulled it out, bulb ohmed ok but no continuity across the socket with bulb intact. replaced socket and bulb, light comes on with switch, energizes without high idle. thanks. mark

 

[MTMUDRUNNER]

Have you ever taken the firewall plug apart? Sometimes a low voltage situation occurs because of dirty contacts with the plug.

From the engine side unscrew the center bolt and pull the plug apart. Use some Electrical Contact Cleaner and an old tootbrush and go to town cleaning both parts.

GM used some type of grease (I don't know what it is) on the plug and over the years between the heat, oxidation and dirt, the grease has turned into a black goo.

I have seen on more than one occasion the GEN1 issues have been because of the dirty firewall plug.

Of course YMMV.

View attachment 450678View attachment 450680

When I first got my 08 I went through tons of info on the site and that was one of the many things I did to her to get pointed in the right direction, maybe I will take it apart again and see what kind of job I did.

 

[MTMUDRUNNER]

I always suggest rebuilding the alts, on a new to you CUCV.

I agree, when I first bought her both gen lights were faults one way or another, I fixed gen2 with a rebuilt one but gen 1 is kicking my butt. I ordered a used but working unit from HBW and I could not get it to charge the batt at all, next I ordered a new one from rare electrical and same problem no gen 1 light at all so I think both are good alts just don't know what the problem is. When I but the old alt back on it charges but like markg says it is over charging. I bought a rebuild kit but it only has some of the parts, I seem to be having a problem finding a complete rebuild kit. If anyone has recently purchased a kit that has all the internals I would like to part #'s and where to go. I will get new heater blower motor, switch, and resistor to el imitate that.
thanks

 

[Warthog]

If you are up to some wiring diagnoses I will walk you thru some tests for the GEN1 exciter low voltage.

It involves some jumper wires and a multimeter.

www.aspwholesale.com has one of the most complete kits for the 27si alternator. Reasonably priced also. I have bought a "few" kits from them.

http://www.aspwholesale.com/index.php?act=viewProd&productId=5137

 

[MTMUDRUNNER]

If you are up to some wiring diagnoses I will walk you thru some tests for the GEN1 exciter low voltage.

It involves some jumper wires and a multimeter.

www.aspwholesale.com has one of the most complete kits for the 27si alternator. Reasonably priced also. I have bought a "few" kits from them.

http://www.aspwholesale.com/index.php?act=viewProd&productId=5137

Sounds good to me on the walk through thanks

 

[Warthog]

It will be tomorrow morning before I can start the walk thru. Please stand by.....

 

[Warthog]

Today we will be working with the GEN1 exciter circuit. First I'll explain the circuit and then move on to some tests.

The GEN1 exciter circuit is on the 12v side of the CUCV system It gets its power from the 12v Terminal block on the firewall and "turns on" when the key is in the run position. Follow along as we trace each leg of the circuit.

1 - From the battery to the 12v Terminal Block





2 - From the 12v Terminal Block to the engine side firewall plug



3 - From the inside firewall plug to the ignition switch

4 - From the ignition switch to the Blower/Heater fuse (The heater fuse controls the blower, GEN1, Oil Pressure light and the 4x4 light)



5 - Heater fuse to the instrument cluster circuit board (ICCB) PIN#5

6 - ICCB to the GEN1 Bulb

7 - GEN1 Bulb to the ICCB pin #8



8 - ICCB Pin #8 to the firewall plug

9 - firewall plug to pin#1 of the two pin exciter plug at GEN1 (brown wire)





10 - Pin #2 (the red wire) at the two pin exciter plug will be hot at all times. It should read battery voltage.

 

[Warthog]

Now for some testing of the GEN1 circuit. We are trying to find the cause of the low voltage on the GEN1 brown exciter wire.

You will need some wire, aligator clips and some male spade connectors.

1 - Separate the firewall wiring harness connection. There is a single screw in the center



2 - Using you multimeter, check the resistance of the brown wire going to the alternator. It should read zero ohms. Attach you meter to the brown wire at the alternator and the labeled terminal of the firewall plug.

What is your reading?



3 - build a jumper wire to go from the 12v terminal block to the in-cab firewall plug. It will plug in to the marked terminal. What we are doing is energizing the 12v system.



4 - Turn on the key and check the voltage reading for the GEN1 exciter circuit. Check the voltage at the marked terminal.



5 - you should be reading 12v (or battery voltage). If not then there is a resistance build up inside the dash wiring.



Have you checked the GEN1 bulb? It needs to be a #168 bulb which is 5watt.

Report your findings.

 

[MTMUDRUNNER]

Warthog, Thanks for the walk through, give me the weekend and I'll report back.

 

[MTMUDRUNNER]

Update, it was cold the other morning and I took her to work so I could work on it in the shop. The heater was not working very good so when I had a chance I pulled the resistor and holy cow was there a mouse nest in there. I ended up pulling the blower motor and cleaned out the houseing on the fire wall. I am currently waiting on parts, resistor and motor which should be here tues. I will see if this changes anything.

 

[markg]

Update, it was cold the other morning and I took her to work so I could work on it in the shop. The heater was not working very good so when I had a chance I pulled the resistor and holy cow was there a mouse nest in there. I ended up pulling the blower motor and cleaned out the houseing on the fire wall. I am currently waiting on parts, resistor and motor which should be here tues. I will see if this changes anything.

you can clean the old motor up, put 12v to it, bet it works fine. use as a backup. thanks. mark

 

[PyroJoe]

A follow up would be nice. I'm having the same exact symptoms. My heater works fine. But the GEN1 light dims the more heater/headlights I use. I rebuilt GEN1 and it changed nothing. My brown exciter wire seems to be functioning properly. But the red exciter wire shows a lot lower voltage than the battery when the truck is running. With the key off, it reads true battery voltage. I believe this is causing my 15.3V overcharge. (Shouldn't a voltage regulator prevent more than 14.6V regardless?)

 

[PyroJoe]

After fiddling with this truck way more than I wanted to, here are the things I've found:

Rebuilt alternator 1 - No results
Cleaned blower motor connection - No results
Cleaned firewall main harness connector - No results
Cleaned 12V firewall block terminals - No results
Pulled 20A Heater fuse - Still get 15V out of the alternator once I rev the motor up

Isn't the exciter wire's voltage supposed to be required to 'turn on' the alternator? Does it mean my alternator is simply shot if it turns on to without the exciter wire? I've seen other alternators that could be triggered with exciter voltage, or a certain high RPM (whichever came first). The only other thing worth mentioning is that I see a significant voltage drop at the #2 exciter wire (red) on the alternator of about 0.4V. Should I run a wire straight from the battery to the alternator and bypass the 12V firewall block to remove that voltage drop?

 

[Tinstar]

I had a similar issue

Turned out to be the large plug on the back of the instrument cluster.
The brown exciter wire end wasn't making contact.
Cleaned and tweaked it.
All fixed and that was a year ago. Still working great !

May or may not be relevant to yours but worth looking at.

 

[PyroJoe]

Swapped alternators and all problems went away. Take my advice and don't use the Amazon alternator rebuild kits.