84 3+3 454 sm465 - No power, fusible link?

Affende said:

got the truck fired up and back home. No idea what is going on with it. There was ZERO power anywhere on the truck (checked the alternator, starter, and junction block) except right at the battery and at the battery isolator.

I piddled with it poking and prodding around trying to try to make sense of what was going on.

yesterday i measured almost 20V on the primary battery and 13V on the auxiliary battery .... went back today and had 1V on the primary and 13V on the aux. I trust the meter, its a nice klein meter so i think the isolator is doing some funky stuff and letting voltage bleed back and forth depending on its mood.

so without going any further, i jumped the positive aux battery over to the positive primary battery and lights and blower motor kicked on (thanks to Dougnsalem for the idea to leave the key on and blower on to help find an intermittent connection).

after that it was a simple jump start (a truck hooked to the primary battery and a jump box hooked to the aux, just the truck on the primary batter wouldnt even try to turn it over).

let it idle 15 minutes to charge the batteries, shut it off and it fired right back up. turned it off, let it sit for 5 hours while i went home and got the wife (to play musical cars) came back and it fired right off.

so ... best i can figure ... there is either a problem with the dual battery isolator or there is a angry ex with a hoodoo doll poking it with a stick.

Im open to ideas and how to proceed from here.

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The best part is, I didn't get a phone call. Probably better for you too. I forgot to mention my "Over the phone diagnostic fee".... Lol

That's cool you got it home! I'd like to hear any thoughts on how you got that 20 volt reading. Especially without it running. That's a weird one there....

OkieFishMan said:

I tell you a story I had with mine, a damn weird one at that. I once went out to start the square. Opened the door and the dome light came on, turned the key the seat belt light lit, went to fire it off and it just barely barked the starter, and everything went dark. No more dome light, not a damn thing. Went to the battery figuring it had bit it. It showed 12.5 volts, so it was good. So I started tracing things backwards from the fuse block. Everywhere but the battery would only show about a volt. I could even put my meter on the terminals and it only show one volt. So I took both terminals off, cleaned the hell out of them and the posts (they were already spotless), put them back on. So now its showing 12.5 volts everywhere, so I figure its fixed and go to start it. It barely barks the starter and BAM everything goes dark again. So I am like what the hell??!! I repeat this process about 3 times and then I replace the battery terminals terminals. I went ahead and cleaned all the wires that connected to the new terminals (they all looked fine) and put it all together. Worked fine. Never did it again. I figure it had to be a bad terminal (never even heard of that) or one of my wires to the terminal wasn't making a good connection. This was on a square I used to have that had been converted to top post. So you might want to make sure that your connections at the battery are all clean and in good shape.

Glad you got it home!

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That is definitely on the list. I plan on rewiring this truck 100% (Hoping to wait until summer) so get rid of the hacked up rats nest that is the current wiring. When i do that, all the ground straps and battery cables will be replaced and or upgraded.

Hell, when i rewired my welder (1968 Lincoln Electric SA200, which are notorious for grounding issues) i ran a marine bus bar as a common ground for everything. I might do the same for the truck. $40 and a couple extra feet of wire is nothing compared to tracing bad connections.

Dougnsalem said:

The best part is, I didn't get a phone call. Probably better for you too. I forgot to mention my "Over the phone diagnostic fee".... Lol

That's cool you got it home! I'd like to hear any thoughts on how you got that 20 volt reading. Especially without it running. That's a weird one there....

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yup ... it has me stumped. The only thing i can think of is that the isolator was some how letting voltage bleed back so the meter was measuring both batteries.

like i said ... electrical work is wizardry to me ... i just dont understand it all that well.

Affende said:

yup ... it has me stumped. The only thing i can think of is that the isolator was some how letting voltage bleed back so the meter was measuring both batteries.

like i said ... electrical work is wizardry to me ... i just dont understand it all that well.

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I had hoped that someone would toss out some ideas on that. I have seen bad alternators put out more, but they were running. Gotta be that isolator....

I'm in the same boat as you with the wiring mess. I've been slowly going through and getting crap ripped out, and put back to stock. Didn't help that I had a wire melt behind my fuse block too. I'll get it straightened out, but its gonna take a long time.... Lol

Dougnsalem said:

I had hoped that someone would toss out some ideas on that. I have seen bad alternators put out more, but they were running. Gotta be that isolator....

I'm in the same boat as you with the wiring mess. I've been slowly going through and getting crap ripped out, and put back to stock. Didn't help that I had a wire melt behind my fuse block too. I'll get it straightened out, but its gonna take a long time.... Lol

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yep ... My 83 C 1500 is the same way. 35 years of rats and farm hands cutting splicing and gluing wires together ... NOTHING works on that truck. Im not even going to bother trying to fix anything on that one until the wiring is replaced 100% ... melted and burnt wires all over the place.

Had that problem with mine. I put a ground wire from the block to the firewall. No problems since. Go figure.

Affende said:

yup ... it has me stumped. The only thing i can think of is that the isolator was some how letting voltage bleed back so the meter was measuring both batteries.

like i said ... electrical work is wizardry to me ... i just dont understand it all that well.

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To get an increase in voltage - as measured at the positive post on the main battery - would require that the auxiliary battery was effectively wired in series with it. That can only be done by the positive side of one battery (the aux in this case) having a conductive path for current to flow over to the negative of the other battery (the main). If the positive sides of both batteries were connected, you would not see an increase in voltage - you would only get an increase in current capacity.

It's not something you'd ever see with only a single battery setup. But - with a dual battery system - it is easily explained.

Say the positive cable coming from the auxiliary had a ground fault (IOW not a dead short - because if that were the case, your fusible links would be burning and the underside of your hood would look like the 4th of July - bad medicine) but just a minor leakage of current into the frame. With a single battery system, that would be no different than leaving your dome light on overnight. It would drain the battery down - to some extent.

But things are different with the other battery in the picture. Now, with the 2 batteries, the current flows out of the one battery - the one that has a ground fault into the sheet metal/frame - doesn't all return to the negative post of the "donor" battery. Some percentage of electrons will migrate over to negative post of the 'recipient" battery (i.e. the one that is well insulated from the frame). That is probably what is going on here. And that is why you saw 20 - and not 24 volts at the main's positive.

That is not to say that you don't possibly have an issue with the relay - the short to ground might be in that relay. But as noted above, even if both positive sides connected together, that would not affect the total system voltage or the voltage of either battery. As a matter of fact that is exactly how the circuit works. What is being referred to as an isolation relay is more correctly called a replenishment relay. I am not too articulate today, maybe the description and wiring dwg below will make things more clear.




The auxiliary battery has no direct connection to the rest of the charging system. It is dependent on the alternator to be recharged - as is the main battery. The difference is, the main and the alternator are always connected and help each other out with carrying the vehicle's electrical load.

The main battery (of any car) only pitches in at the beginning (i.e. when it supplies the power to the starter). After the engine is running, it just sits back and lets the alternator do the bulk of the work. There are times when demand exceeds the alternator's capacity - like if you are running every electrical component in the truck and playing the radio wicked loud - then the battery has to get off its lazy ass and help out. But that can't last long, because the battery is only a storage device and cannot recharge itself.

Without being there with my Fluke, I can only speculate that the situation described above is accurate. What I would do if it were my truck - and you had no immediate need for the extra battery - would be take it out of the equation and see what happens. To do that is as simple as disconnecting the lead that is bolted to the auxiliary JB and the positive cable from the aux battery positive. The relay itself will still operate - and the contacts will close - but no with no cross connection from the main to the auxiliary, no current will flow.

Then, if things clear up, you can assume there is a problem in the aux positive wiring (read, ground fault). If the main continues to struggle, disconnect it from the main JB. Be sure you disco the load side, not the line side. The rest of the system will still need to be fed with power and that is how it gets it.

If you still have charging problems, disable the relay itself - by yanking the radio fuse - that will cut control power to the coil.

I also have one of the Klein VOMs and was recently using it to check voltages on an old radio. Voltage ranged from 400/800 volts AC to 300 volts DC, to about 5 volts DC, so it varied a lot as I checked out the system.

I had problems with the meter auto-setting (or me pushing the wrong button) and it was on AC vs. DC sometimes, which meant I first thought I was getting really screwy voltages. Then I checked the meter reading and found the little squiggle sign instead of a line, which meant I was in AC mode instead of DC.

For car voltage troubleshooting its probably easier to use one of the cheap VOMs from Radio Shack or Walmart. They are so simple that its really hard to set them wrong, and if you happen to wreck it, you just go back and spend $20 to replace it. The only catch is that to measure resistance you usually need to have good batteries, and you must zero it before you start, since the drop in battery voltage is used to "calculate" resistance.

Bruce