HMMWV electrical help needed

[17 Legion]

I put some new guages in the HMMWV. The old ones were hard to read especially at night so these new ones went in and I lost some of that "been in a war zone" pantina. My old voltometer guage only had one connection in use, the new one has two. I reconnected every wire correctly and still have the same "yellow" reading. The reading was the same on both old and new guages. I've never had to charge the batteries. Am I missing a connector? This reading seems low. First picture shows guages at idle engine speed. Thank you for all the help in advance.

 

[emmado22]

Check the generator output. Perhaps the gauge is correct, with a low readign due to low input.

 

[deuceaid]

its hard to see in the picture, but I am guessing the one on the right is the old one, does it have some kind of grounding bar going from the far right terminal to the mounting screws?

 

[17 Legion]

Yes. In the original post, the one on the right is the old one. Here's a better picture. Is this the way all voltmeters are wired on 24 volt military systems? How are other members guages on this board connected. Any HMMWV owners with low volt readings?

 

[jwaller]

I'm a v owner but never had that issue. Does your truck have the aux grounding harness? if not you need to make/install one.
Have you used a real voltmeter to check what your getting to see if it's a gauge error or an alt issue?

 

[deuceaid]

I think Your missing a ground wire.... a safe way to check would be to place a piece of wire on that bare terminal... run it out to a 24 volt light bulb, and then ground the other lead of the light bulb....... either the bulb lights up and/or the meter swings a little. (just think of it as grounding the meter,,, but the bulb acts as a current limiting safety) if you have a test light probe that you can put a 24v bulb in that would be perfect.

 

[nattieleather]

do you have the -20 manual? Read the troubleshooting section for low read on the altinator gauge and follow the steps to find the problem. If charging correctly the needle should be hitting the white line in the middle of the green section. Also the manual will show you how many wires are suppose to be going to the gauge and where that wire goes. I.e. to ground or to a voltage source etc.

 

[sandcobra164]

I noticed the temp gauge is bottomed out, my work truck drops in the yellow when the glow plugs kick back in after a cold start. It'll jump back up to green when they release and then jump back to yellow when they engage again. After all that, it'll jump just to the right of the line in the green. If the truck is not driven much and does this while warmed up, I'll check the alternator and especially the voltage regulator on top of the alternator. It's got 2 wires going to terminals on the side of it and a connector with several wires that plugs into the end of it. Be sure to get one for a HMMWV, the ones for the MRAP Caiman's, Buffulo's and the FMTV are a different NSN, they look about the same but are slightly different from what I've been told.

 

[17 Legion]

Update:

I checked the voltage at the alternator with the engine running and read the first picture. Then with the engine not running and the ingition on.
I got the same reading both times so that means the reading is for the batteries. Alternator was the taken off to be diagnosed.

 

[17 Legion]

I also discovered this loose wire. The number on this tag is 568. Any idea were this should be attached? The only two wires not connected are this number 568 and the hard wired connection off the alternator.

 

[Warthog]

According to the Universal Wiring Numbering Guide, 568 is the Ignition Switch to Alternator wire.

I haven't found the HMMWV wiring diagram yet but will keep looking.

 

[Warthog]

Found the wiring diagram. It is in the back of TM 9-2320-280-20-3.

Can't tell by the pictures but it looks like the loose wire is suppost to plug into the male connector.

VERIFY all the wire numbers before proceeding.

 

[nf6x]

A reading of 23.2 volts while the engine is running indicates that the alternator is not charging; it'd be up around 27.6 volts if charging correctly. A broken ignition-to-alternator wire would certainly cause that symptom, so that might be your whole problem. Consult the TMs and study the pictures carefully to make sure you correctly identified both ends of the correct circuit. It looks to me like your dash voltmeter is correctly indicating a problem, which you have verified with a multimeter and visual inspection.

Good luck! I hope that the broken wire is the whole problem.

 

[jwaller]

as others have said 568 needs to be connected and is in fact the wire we discussed on the phone. that is the wire that tells your alt it's time to start charging.

 

[17 Legion]

Warthog, and others, thank you for the reply. That's the same information I just now found. We just relocated so finding all my docs can be a challenge.
As always I knew this board and it's members would be reliable help.
I'm having the alternator rebuilt and will reinstall it later this week.
I'll post who re-built it for me after success. Maybe someone else will need alternator help in the future.

 

[17 Legion]

Well guys, I'm going to pick-up the still busted alternator. It charges without the regulator, but the guys who have it can not figure out how to get it to work with the regulator in place.
They even talked to the Prestolite rep. Still nothing.
Any ideas? I need to get this one working and not buy a new one. I'm in NC,
so any locals get their alternator rebuilt please chime in with who does it. Really helps if they work on 28 volt alt.

 

[emmado22]

There has got to be some auto electrical shop around Ft Bragg that deals with these on a daily basis. Google it and then call them!

 

[17 Legion]

I'm on that already. Just trying to avoid shipping a forty pound unit. Good tip and thank you for the quick reply.

 

[Army Kid]

Warthog, and others, thank you for the reply. That's the same information I just now found. We just relocated so finding all my docs can be a challenge.
As always I knew this board and it's members would be reliable help.
I'm having the alternator rebuilt and will reinstall it later this week.
I'll post who re-built it for me after success. Maybe someone else will need alternator help in the future.

Just an FYI, I had the exact same issue.. volt gauge always in the yellow.
I started the truck, warmed it up, turned the headlights on, engaged the accelerator 'cruise control' handle to keep it just above idle, removed the set-screw next to the wire terminals on my prestolite alternator, plugged my Fluke meter from ground to hot, and spent about 20 mins trying to 'breathe' on the adjustment screw with my screw driver to adjust the voltage to within spec. (28V)
(Just followed the TM below) & now i'm in the green & everything is perfect.
1. Using hex-head driver, remove pipe plug (12).
2. Connect battery ground cable (para. 4-73).
3. Start engine (TM 9-2320-280-10).
4. Raise engine speed above idle.
5. Put a load on the alternator by operating driving lights (TM 9-2320-280-10).
6. Using a multimeter, check alternator (15) output voltage. Connect black test lead to ground
lead 3B (1. Connect red test lead to lead 5A (16). Output voltage should be 28 volts ± 0.5 volts. If
adjustment is required, go to step 7. If no adjustment is required, go to step 11.
7. Turn adjusting screw (17) counterclockwise to increase voltage or clockwise to decrease voltage.
8. Turn off driving lights (TM 9-2320-280-10).
9. Return engine to idle.
10. Stop engine (TM 9-2320-280-10).
11. Apply sealing compound to pipe plug (12) threads. Using hex-head driver, install pipe plug (12) and
tighten to 30-40 lb-in. (3-4 N•m).
12. Remove battery ground cable (para. 4-73).
13. Seal terminal connections using adhesive sealant.
14. Install terminal cover (7) on alternator (15) with two lockwashers (5) and screws (6).

 

[Retiredwarhorses]

As Army pointed, the adjustment to the Gen output is easy....A good way to see what going on is to take voltage measurement at the batteries first with engine off, you should have 25-26volts pos of battery one to Negative of battery 2. Start the truck and take same measurement...you should be getting 27.5 volts or so....if nothing...you have no Gen Output, if you see that you are getting Gen output but your gauge is not on the in the Green on the white line, go to the Gen,take of the wire cover off, unscrew the Hex cap, clamp your leads on the Groung lug and Pos Lug of the Gen output with your Meter, you should see the same voltage as you did at the Batteries with engine running, put a phillips head into the hole where you removed the Hex cap, slowey...and i mean slowly turn it till you see the voltage go up...have your kid or wife errr whatever sit in the cab and tell you when the needle is in line with the white line....done.
Also, the 60amp Gen is the easiest and carefree of the Generators...if you have the 100 or 200amp...get rid of them. you will need a new Gen bracket for the 60amp and rear Gen support bracket....Just MHO.