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Gen 1 light never comes on

Stagg

Member
109
0
16
Location
Kansas City, KS
Yes I replaced the bulb(s)...

So, after many days of wandering the SS site looking at Alternator threads, and studying the TMs and FMs.
What exactly is happening if the GEN 1 light doesn't come on at start up (or ever for that matter) I'm curious since I roughly understand how to fix the problem but not necessarily what is causing it.

Gen 2 comes on and goes out like it should. And the voltmeter in the dash is reading low green/high yellow. So one of the alternators is probably bad for some reason.

I've replaced the bulbs and cleaned the contacts on the "circuit board" and have new 6TN batteries.
Am I reading it correctly in assuming then that the driver side (gen 1) alternator is bad for some reason?
Or is there a simpler wiring type problem that could be the cause?
 

maybefixit

New member
106
1
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Location
Hamilton, Ohio
First a little disclaimer:
I've never worked on a CUCV. I'm offering some general advice, but it's in the dark, and please use all this with a nice dessert and your TM's open.
Apologies in advance if you already know / have tried the following items.

I'd recommend checking the exciter wire (small wire) on each alternator, with the key 'on' and engine not running, with a voltmeter. Check for ~12v relative to alternator body. Check the (working) 2nd alternator first, then the (broken) one.

I have noted a lot of cases where the grounding of an alternator can cause these type issues. A 1986 Olds I sold to a neighbor was doing a weird thing, where the alternator would clearly not charge, but would test fine, and would work after reinstallation for a couple days. Adding a #8 ground wire from the alternator body to engine case cleared it up. That was on a 12v system, Not A 24V Military System.

I was going to say that you could add a ground wire, but that may be a mistake, if the alternator in question is purposely made to have a negative side that is not at engine or vehicle frame ground. Check to see if one alternator body is at +12v relative to engine or frame, maybe there is a dedicated ground connection direct to one of the batteries. (I've never read the TM's for your vehicle).

As a side note, I've noted that on 10+ year old fuel injected cars, a good cleaning of any ground wires I can find (with the car Off) really helps idle and engine smoothness. Just disconnect the wire, use some sandpaper on the connection to brighten it at the frame, bolt, and wire connector, and reconnect. Some sensors only have a 1v potential, so a rusty ground can make a difference. To keep them from re-rusting, a little petroleum jelly will keep them fresh.
The safest way to do a ground cleanup is to have the battery ground disconnected when you pull ground connections, and remove/clean/reinstall one at a time.

Hopefully the guys with hands on experience can help with more specific info. :)
 

emmado22

Moderator
Super Moderator
Steel Soldiers Supporter
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Mid Hudson Valley NY
I was going to say that you could add a ground wire, but that may be a mistake, if the alternator in question is purposely made to have a negative side that is not at engine or vehicle frame ground. Check to see if one alternator body is at +12v relative to engine or frame, maybe there is a dedicated ground connection direct to one of the batteries. (I've never read the TM's for your vehicle).
IF YOU ADD A GROUND WIRE TO THE PASS SIDE ALT, YOU WILL GET A SPARK SHOW LIKE YOU HAVE NEVER SEEN BEFORE... IT HAS AN ISOLATED GROUND..

The advice on making sure that the correct grounds are making a good connection, thats EXCELLENT advice...
 

Croatan_Kid

Member
691
2
18
Location
New Bern, NC
Neither of my Gen lights ever come on, never have. Both bulbs are new, both alternators have always charged. It doesn't bother me one bit.

Is it right? Well, maybe not.

Does it still work? Yessir!
 

HikerLT

New member
32
0
0
Location
brookline, nh
I have the same issue on the Gen 1 light never coming on. Is there any thread or details that outline the expected sequence of Generator lights, Voltage Meter measurement, etc. that you should expect on a normal start sequence.

To the original Poster - did you ever get the problem fixed, and what was the root cause ?
 

Stagg

Member
109
0
16
Location
Kansas City, KS
I was just looking for this thread... solved the problem. Actually solved two problems at once!
The Gen 1 light runs through the heater fuse, when I fixed the heater (and stopped blowing fuses) the gen 1 light started working again, along with most of the dash lights.

So after all the hassle it turns out to be a fuse :roll:
Actually figured it out as I was solving the problem when I found the PS article, here on SS, about alternators. Its a good trouble shooting guide.

Now that my batteries charge, I can reconnect my glowplugs and start enjoying my truck!
 

BobM

Member
598
6
18
Location
Fillmore, Indiana
OK. My gen 1 light does not come on PART of the time. I have cleaned all the connections, put a new end on the ground wire and it worked, but the light glowed dim with heat and lights. I replaced the heater blower that was dragging and the light would not come on at startup. This lead to a flat battery. I cleaned all the connections again and the light came back on, but still glowed dim with heat and lights. My cheap voltmeter showed no difference between the volts with or without the heat and lights on. It showed 11 volts with engine off and 11-12 volts with the engine running. I tested two other trucks and the meter showed the same info on them.
I decided to pull the alt and have it tested. When I did I found that I had left the brown wire off that is normally on the post with the red wire. I put that wire back on and now the gen 1 light will not come on.So I again cleaned all the connections, replaced gen 1 lightbulb and even shined up the contacts on the heater fuse. But still no light.
My heater motor works fine, so the fuse must be okay, right? Can the alt being bad cause the gen 1 light to stay off?
 

jwaller

Active member
3,724
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38
Location
Columbia, SC
I would bet that when running you should be seeing ~14V to each battery. 12 is simple batt voltage and your not getting a proper charge.
 

BobM

Member
598
6
18
Location
Fillmore, Indiana
I would bet that when running you should be seeing ~14V to each battery. 12 is simple batt voltage and your not getting a proper charge.
You are probably right. But this cheap multi meter that I have may not be reading exactly right either. I found that the small wire that goes into the plastic clip on the driver's side alt was still dirty. When I cleaned it (AGAIN!) the gen 1 light came on before starting. I drove it to work tonight and no gen 1 light even with heat and lights.
I'm not saying it is fixed yet. But maybe.....;-)
 
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