03' 7.3 No Electrical Power

[clicker44]

Hello! I have a new to me 2003 7.3 EB. The van is cherry but had been sitting for a while when I purchased it. I bought the van, drove home 14 hours (slept overnight as well) with no issues (ie...van started the next day).

The only thing I noticed on that drive was when I put the key into the ignition and then did the requisite half-turn for the diesel, the van gauges and lights would do their normal thing (ie...lights light up and gauges move) and then I would hear a sort of click and they would do it again. The second time they would act normally and the van started fine.

Fast forward a few weeks and the van has been dying if I do not keep it on a charger (haven't been driving it at all). I had the battery under the hood load tested (Interstate AGM 850 CCA) and it came back good. The battery on the frame rail was toast (led acid. Completely dry. 7 volts), and the house battery is toast as well.

I replaced the battery on the frame rail with an exact match to the one under the hood (Interstate AGM 850CCA), cleaned all of the connections (lots of corrosion) and reinstalled everything. I am getting 13V at the terminals.

Once I was finished, I put the key in the ignition and got a nice "ding ding ding" sound and when I went to my half turn the dash lights and gauges went haywire then all electric died. Now I have no electric anywhere in the cab (no locks, no dome lights etc...).

When I did the aforementioned start, I had the isolator CLOSED so that (at least in my head) I would be only using the starting batteries to start the truck.

I re-attached the house battery and opened the isolator and tried again....nothing. But...all of the house items work (ie...fridge and sink pump turn on etc...). I know the house battery is bad (already have a replacement on the way) but there is enough juice to turn on the fridge etc.

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I un-did all of my work to make sure 100000% the cables were going to the correct terminals (they were correct).

On my van I have a house battery (4D) ---> frame rail battery (AGM 850CCA ---> and a terminal next to the frame rail battery where the POSITIVE cable from the house battery, the frame rail battery and the engine battery meet.

I cleaned the hell out of that terminal and even removed the house battery positive cable to see if perhaps that was the issue. No luck.

The weird part is after removing the house battery POSITIVE cable from the mid-ship terminal, I was able to put the key in and get a weak "ding ding ding" but this time I turned on my fog lights (no ignition turn at all) and they turned on very weakly, but after 30 seconds the van went completely dead again.

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The internet is telling me it is potentially a bad ground somewhere? I was thinking fuse? PCM? Relays? Maybe a rodent chewed a wire over the course of the last few weeks when she was parked? Not even the key FOB responds. 100% dead.

Thank you in advance if anyone can help!

[REF]

Your toasted house battery is most likely drawing your starter batteries down, the original battery isolators that they used to install are prone to go bad as well, which may be causing an open circuit from your house to your starters, it’s the blue aluminum finned brick under the hood, normally found on the drivers side near or under the coolant reservoir.
Many have replaced with a blue sea separator, I replaced mine with a sure power separator that’s held up so far but are not as good as the blue sea.
Also check the output voltage of your alternator

[clicker44]

@REF -- Thank you very much for the reply! Is it safe to assume that my van would not start without a charged house battery if the isolator is bad? Hypothetically speaking, if the isolator was good, would I be able to turn it off to isolate the house battery and starter batteries and then start the van with no house battery attached?

Also, so strange....I stopped working on this and when I went out to the van this morning the key FOB worked to unlock the doors. I am sure if I put the key in the ignition that the van would die again....but its almost as if something is charging up? Right now I have only 1 battery connected (under the hood) as well.

The van has a Blue Sea isolator mounted near the inverter. Any easy way I can check if the solenoid is good? I out a multimeter on it and its showing good voltage at the isolator.

My new house battery arrives today so hoping connecting all the batteries does the trick!

[REF]

Others might chime in with more intell, but your van will certainly start without the house battery hooked up, keep in mind that it takes a lot to crank over a diesel, especially the 7.3, so while it’ll crank and start up on only 1 of the starter batteries, if it’s fully charged, it’ll be less stress and better once both starters are hooked up.
If in fact you’ve got a blue sea separator, I doubt that’s the issue. Often times, and I don’t know if this is a function of the blue sea unit, a separator or isolator will not function or remain in an open or default position if there’s low voltage on one or both sides of the batteries, so having a toasted house battery might be part of the issue. I’d wait to do anything else until you’ve got all your new batteries hooked up.

[clicker44]

Great knowledge! Thank you.

[arctictraveller]

If your house battery is dead, and the separator is closed (ie, connecting all batteries together) it would most definitely kill your start batteries. There's really no reason to have the house connected to the start's until the engine is running unless it's an emergency and the starts are discharged. Make sure the starts and house batteries are not connected together and then put a charger on the start batteries. Once fully charged, you will quickly see if that's your issue. Also, if your frame battery is new, but the under hood battery is not, the older battery can discharge the newer one, unless the older one is in really good shape. Batteries connected in parallel should always be the same type and age.

[Glenn P.]

I've owned diesel trucks or had them in the family for the last 40 years. One thing I was always told is that you ALWAYS replace BOTH batteries (talking about the starter batteries here, not the house battery) at the same time. If you had a completely dead battery reading 7 volts on the frame rail, and both starting batteries are tied together via a substantial cable, the bad battery will suck the life out of the "good" battery until it too is compromised. Now I understand you had your battery up top "checked" but I find it very hard to believe that one battery tied to another in parallel would still be good with the other so bad. The good one would constantly be trying to charge the dead one. Lets go back to the rule of you always replace diesel batteries as a set and stick with that. Maybe the one up top is good enough for regular car use but I seriously doubt after what you have described that is a solid battery any longer, and definitely not one I would trust when traveling the back roads where you will be way out there and all by yourself.


Just my thoughts here. I do not have any experience with house batteries and isolators on these trucks but 40 years of diesel experience leads me to trust the old adage of always replace the batteries in pairs. Cleaning up those grounds is also an excellent plan, corrosion can get the best of you. The 7.3L has multiple grounds, check them all. I also might suggest the use of a conductive battery grease/dielectric grease on the terminals as well as on all the grounds.

[winnievan]

Yup -- always replace your batteries in pairs... even if the other one is in good shape -- it won't be as strong as the new one and it'll bring it down and shorten it's life.

Also -- check that the connection to your fuse box is solid. There is a busbar style connection there that when it comes loose can cause a non-start condition.

I'd remove your house battery and drive the vehicle for awhile... if there isn't any problems.. then you probably have found the culprit.

Don't cheap out on batteries for the 7.3 -- they need lots of power to turn over properly.

[clicker44]

Thanks everybody for responding...much appreciated.

Update:

I now have (3) brand new batteries:

- (2) brand new matching Interstate AGM's for under the engine and on the frame rail.

- (1) brand new Lifeline AGM 4D for the house battery.

- I cleaned the ground by the battery under the hood and replaced the frame to body ground on the frame rail.

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I hooked everything up today and still had the exact same problem. After connecting everything I clicked the key FOB and heard the locks unlock and lock (good sign) then I stuck the key in the ignition and got a ding ding ding (good sign) then I went for the half turn and the dash lights lit up and then everything died. Now no power at all again anywhere in the cab of the van (no headlights, fog lights, radio, dome lights, fog lights etc...) absolutely nothing.

The house items work! The fridge turns on and the water pump turns on amongst all the other various house items.

I tested the isolator which is mounted near the inverter by turning it "on" (vertical position) and then trying to turn on the fridge, water pump etc....nothing. When I turned it "off" (horizontal position) all the house items work. So I am thinking that isolator is good.

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Any ideas of a fuse or anything that would be the all controlling fail point for all power to the cab? I tried the isolator "off" (ie...adding the house battery into the starting circuit) and still no change.

The strangest thing is if I let the van sit for a few hours, I will be able to click the key FOB, and turn on headlights for a moment etc...before the cab goes completely dead.

Adding to the mystery is that this exact situation happened BEFORE I went to replace all the batteries....I knew I needed batteries but have been so busy I just left my NOCO Genius charger on the battery under the hood and then when I needed to start the van it started....until finally it did not start (did the exact same thing) and since then I now have 3 new batteries and am dealing with the same issue.

The only thing I can think of that I did was do a half-turn on the ignition with the charger attached (this was when the issue started). Not sure if that is coincidence or if I did something bad by doing that. The charger I am using is a NOCO Genius GB50 (it has a JUMP START feature on it so one would assume it is OK to turn the ignition on with the charger attached).

Any ideas? --- THANK YOU!!!!

[Scalf77]

It does not sound to me like the item you think is an isolator is actually the isolator. A 7.3 probably started it's life with a diode based isolator that would generally be installed in the engine compartment (right side)

-greg