So, electrical gurus how are we?

So just noticed this last night after doing a glow plug and relay change - however, that's not to say it hasn't been happening before.

2001 F250 7.3L diesel 280k miles

So the large gauge wire on the back of the alternator (assuming it goes to the battery) - was dark and didn't have time to trace last night) was smoking and super hot after start up - didn't run the engine for long enough to see if it cooled and was therefore maybe a starter related issue.

Whats the relay in front of the glow plug relay? There seemed to be a small gauge (1-2mm thick) wire connecting the two that had pulled out and we re-connected last night - not sure of its purpose - could be a red herring.

Bunch of random power wires for amps radio etc that the truck no longer has running from passenger side battery.

Thoughts - process for eliminating and fault finding this issue? Could it just be its not grounded somewhere correctly??

Cheers

Simon

 

With everything off and the truck just sitting there, pull the battery cable off one battery and check both batteries with a good digital meter. They should be in the neighborhood of 12v or a little higher. If you find one is 10v, you have a dead cell and that would overwork the alternator.

 

Could also be, The alternator is OVER charging. How is your battery health? What loads do you have when key hot? Could also be what Franklin2 said, Bad battery.

 

That's true, with both batteries hooked up and the engine running, again with a good digital meter read the battery voltage, one battery will do. It should be 13.5-14.5 volts. If it's 15v or higher, the alternator is overcharging the batteries.

 

Overcharging alt. Could be killing the battery which is pulling an intense load causing the alt. to overcharge, etc etc. You get the idea. Start the truck then pull them off and let it run. It won't damage anything. Do as frank said but check the alt. output with no batts. Best option is to pull the thing off and have it tested on a bench.

 

Think we nailed it, the nut looked like it came loose attaching the wire and there was some serious asking going on. Pulled everything off took the alternator inside and cleaned everything up and re attached - seems to be good so far touch wood!!

 

No, never do that. Never take the battery or batteries loose with the engine running. If the alternator is running away, it can damage a lot of stuff. Been there, done that.

I had a old GMC pickup that I was having problems with, and I had swapped in a later engine with a HEI ignition. I pulled the battery cable off while it was running, it kept running for about 10 more seconds and then quit, never to run again till I replace the ignition module.

If there is a problem with the charging system, the battery acts like a storage tank and gets hot and boils, but it helps keep the voltage down to a reasonable level. You can actually get over 100v out of a alternator with no battery on it if it's wide open full charge.

 

The battery always acts as a filter and prevents the spikes and sags, and smooths the DC waveform, not just if there's a problem. You couldn't pay me to pull off the cables while running, at least on anything made this century. Maybe nothing bad will happen, but that's not the way to bet.

Battery charging voltages are also temperature dependent as well. In extreme cold the internal resistance of a battery is a lot higher and so takes a higher voltage to reach full charge. The charge tables run a little above 15 volts at sub zero temps. Keep this in mind before condemning an alternator or voltage regulator.

 

So there's a bit more to this issue.

The alternator is throwing out 13.6v at idle no extras running like lights blower and such.
About 4 days ago discovered passenger side battery bad after battery light flashing and had the batts tested. Replaced with new motor craft under warranty - couldn't afford to do both. Now Have older battery passenger side, new battery driver side.

Yesterday drove 5 hours and about hour 3.5 battery light starts flashing again - only power draw for drive was radio, no lights etc

Stopped for the night and jumped into local autozone and can't get reading on new battery and older one is barely charging and alternator test says alternator bad? I borrowed their machine and got the 13.6v testing off the back of the alternator to engine block

I will test the grounds etc on the batteries today but I was hoping people could follow my thought process for a second...

Electrics isn't my strong suit but i sort of understand the parallel battery bit and it seems odd that the drivers side is draining/ not charging new out the box and likely dragging down the passenger side and maybe giving the flashing battery light. Things must have been OK the last four days while the new battery had charge?? As no flashing battery light

So anyway amongst other things, when we fixed the glow plugs and gpr there was a wire between the gpr and the relay in front aih? And it was broken - I made an assumption it should be fixed and I'm thinking that's not the case now - pic is below but could this be the cause of my battery issues?? I had this eureka moment at 0135 this morning and got up and took the picture, hoping it's a eureka moment or I got out of bed for nothing ����

 

Can't think of a reason why you would have a small wire connecting the two relays. You would have a large heavy wire connecting the two, or large wires going to the same place, this is the supply for the glowplugs. But not the small wires.

If you still have fairly warm weather outside, your truck should be able to start on one good battery if you suspect the other old battery is bad. I did it all summer on my diesel with one good old battery I had laying around till I saved enough money to buy two new ones from Walmart.

 

If you can't afford a battery, can you afford what an alternator or other electrical parts cost? Not trying to beat up on you, but recall two batteries in parallel is just (electrically) a larger ampere capacity battery.

Both "cells" have to be the same voltage and internal resistance or one battery will hog the charge current and outgas excessively. While mismatched cells will work i.e. It will start, it's going to cause problems, as you've discovered.

 

I'm hearing ya, both were still under warranty just one was bad and the other was tested good, so I agree while not the best option, at the time it was my most financially efficient . So I ran a couple of checks this morning, both batteries test 12-5V still connected to the truck but across the stubs on each battery - just thought should I test disconnected? Checked continuity across alternator to passenger battery 0.5 ohms. Will check driver one later. Ground on passenger appears all good but will remove and clean, ground on drivers covered in oil and dirt so I'll remove and clean. Need to flash up truck and check double wires out the back of the alternator to check for 12v on each?? Double check alt output standard and fully loaded. Anything else I should look at???

 

Replace the other battery with a new one identical to the installation 4 days ago. Same date code.

Replacing just half of a battery won't work very well. Charge each one up thoroughly with an outboard charger for 12 hours, say. Install. Done. Otherwise.. not so much. Can you say "continuing saga"? Maybe that's not what you want to hear, but.

 

So voltage regulator was toast, $35 off eBay with new bushes etc, then found new alternator for less than $80 from a US aftermarket place so went with that. Batteries on charge whilst alternator arrives in the post. Interesting FYI for you all, at 5000ft no battery light flicker at all, but problem obviously still there. Over 6500ft elevation and battery light flicker is there - totally wierd!!

 

Just an FYI, overcharging wouldn't cause the alternator wire to get hot enough to melt the insulation, assuming it hadn't been replaced with one too small. Higher voltage (which overcharging is) would mean you could even get away with a smaller cable.

While sorting charging issues, NEVER disconnect a battery or alternator cable when the vehicle is running, you're very likely to fry your diodes.