Humvee won’t start, no wait light

[bercler]

Quick background: 1986 Humvee made some starter noises the last few start ups, the last time I drove it all the electronics started working sporadically while driving, coming in and out. I assumed it was a bad ground and added a supplemental ground harness. Next attempted start, no wait light and no crank, nothing from the ignition. Now I assumed it was a control box issue, ordered up a smart box, new glow plugs, and a new keyed ignition. Next attempted start up, same results…nothing. Pulled my batteries (blue top Optima’s ) did a thorough exam of them, load tested, charged and re-installed. Next guess was neutral safety switch, pulled the shifter (5 months old) and everything looked good and functional, re-installed, same results. Hooked up my old neutral safety switch to double check, same results. Tried to bypass the smart box on startup and put a jumper between terminals S & T on the diagnostic plug, same results. Any insight or ideas would be highly appreciated.

Thanks

 

[Mogman]

Welcome to the SS forums!

 

[Mogman]

First IMHO the supplemental grounding kit is a "patch" that does not cure bad grounds, because you must disturb some of the original grounds to install the kit some may inadvertently stumble across the real problem they are having and think the kit fixed the problem.

The kit can also cause unintended ground loops that can actually be dangerous, if it were up to me the sticky would be removed to avoid having it be the first thing a newbie sees.

Every device on a HMMWV has a ground path from the factory and none depend on the aluminum body which is one of the excuses I hear over and over to justify the "kit"
So the first thing you should do is clean and check all the grounding points.
The second thing is to actually troubleshoot each problem as you come to it and not just throw parts at it, doing that can cause more issues that will make troubleshooting the original problems much harder.
You can "jump" the starter at the diag port that does not depend on anything else but good battery connections (positive and ground) to the starter, the starter and the batteries and the two wires from the solenoid/battery to the diag port.
If you cannot get the starter to operate it is one of those few items.

 

[bercler]

Thanks for the advice, I will revisit and clean up all the grounds and go from there.

 

[Mogman]

Remember to disconnect the batteries any time you are doing electrical work.

It is also a good idea to pull the harness from the TSU (temp sending unit) on the right side of the water cross over to disable the glow plugs while working on electrical problems until you are actually going to try and start the truck. otherwise ANY time you turn the ign switch to off you must wait at least 90 seconds to go back to run or you can fry the glow plugs.

The keyed switch is usually a really bad idea and has caused many expensive failures on Humvees the switch is subject to more voltage and current than most switches can handle and can even lead to fires.

The main battery cables have connections on both the inside and outside (in the tunnel) of the battery box

 

[Mrgior31513]

So the first thing you should do is clean and check all the grounding points.

The keyed switch is usually a really bad idea and has caused many expensive failures on Humvees the switch is subject to more voltage and current than most switches can handle and can even lead to fires.

I don't know anything about HMMWVs, but Mogman is on point IMHO.

I will say that every vehicle that I own I add my own additional grounding points. NOT replace, I actually always add them to engine, transmission, transfer case, etc. I've seen people fry brand new transmissions on full sized trucks from poor grounding. Poor grounds can create both arcing and electrolysis and do very weird things. With intermittent electrical issues: it's my first go to.

Switches are best used in conjunction with relays, I don't even put 5 amps through a switch. Relays are relatively cheap, and electrical fires are not. A 120 amp relay is about $12. A higher quality 200 amp relay is about $40.

 

[TOBASH]

Get rid of the keyed ignition!

Make sure you get power at the ignition wires.

Clean and check your battery connections.

 

[Mogman]

S and T at the diag port should activate the starter, if not it is the batteries, the starter or the cables.
Check the voltage at T using the block as a ground for the meter while connecting to S if it stays at 24V and the starter does not activate then it is likely a starter/solenoid issue or the connection to the solenoid on the starter, wire number 74.
Be careful when tightening the battery cable nut on the solenoid as if you over torque it you can break the solenoid

 

[Mogman]

Also remember the shunt that is mounted in the battery box is in the negative lead, sometimes folks assume it is positive, it also has connections inside and outside of the battery box.

 

[bercler]

Found the issue, bad connection and arching on the shunt. Cleaned it up, put a new bolt in and it fired right up. Thank you for the responses and tips.

 

[Mogman]

Believe me I am not trying to be harsh but we see this type of thing happen all the time to folks new to the HMMWV world, too bad you did not come here first, you spent allot of money getting to that $.50 fix.

Keyed Switch

I have read alot about the keyed ignition switches not being any good. Do they know make one that is any good?

www.steelsoldiers.com

Please look at post #18, this is one of the very common issues with the keyed switches, there are MANY stories like this up to and including burning trucks to the ground.
If you are bound and determined to have a keyed switch post #17 would be a good option.

 

[bercler]

Believe me I am not trying to be harsh be we see this type of thing happen all the time to folks new to the HMMWV world, too bad you did not come here first, you spent allot of money getting to that $.50 fix.

Keyed Switch

I have read alot about the keyed ignition switches not being any good. Do they know make one that is any good?

www.steelsoldiers.com

Please look at post #18, this is one of the very common issues with the keyed switches, there are MANY stories like this up to and including burning trucks to the ground.
If you are bound and determined to have a keyed switch post #17 would be a good option.

Im ok with it, I upgraded my control box so I don’t have the start up voltage cycling which would sometimes trigger my push button light switch to not work, new glow plugs and a new ignition switch from MME. I’ve ran an ignition switch for 3 years with no issues and this one is definitely an upgrade to the one I had. I made my own supplemental grounding harness for about $30. I like the keyed ignition and also have a hidden kill switch for extra security since I drive into town often. I’ve upgraded almost all of the electrical components minus the harness.