Battery light on

[verotik]

We have a 2001 E450 with the 7.3L. We've been doing our buildout and are almost done and getting ready for a trip in about a month. So we hadn't started it in about 2 weeks, but before everything had ran fine. Went to start the bus and it was turning over real slow and then battery was dead. No big deal, put it on the charger overnight and go to start it in the morning, still acting like the battery is dead, so i got out the multimeter and the battery is showing 12.8V. I get under the bus to look at the starter and notice that the solinoid on the starter is missing one screw and the other one is in there but not screwed in, so the solinoid is just kinda hanging there. I tighten the one screw and go to start it and it starts up fairly easily, but still a little sluggish, so i went ahead and ordered a new starter that will be here in a few days, but the battery light is on now. The terminals were pretty corroded, so i went and bought new terminals and put them on with the anti-corrosion gel, still starts up, but battery light stays on. It was a handicap wheelchair bus, so it has a high output alternator. There is a shunt on the drivers side by the power distribution panel where the alternator output goes and i checked the voltage there and it is only putting out about 12.2V. That doesnt seem like near enough for me. Would that be causing the battery light? I've googled and havent come up with much other than moving the pigtail around and such.

[Twigg]

With the engine running, the voltage in the system should be 14.2 to 14.4V.

If you are not getting that something is wrong.

As a new alternator is coming I'd fit it, check all the cables and grounds (esp. the grounds), and probably replace that shunt too. You can decide once the alternator is replaced.

[verotik]

Originally Posted by Twigg

With the engine running, the voltage in the system should be 14.2 to 14.4V.

If you are not getting that something is wrong.

As a new alternator is coming I'd fit it, check all the cables and grounds (esp. the grounds), and probably replace that shunt too. You can decide once the alternator is replaced.

I havent ordered a new alternator, i've just ordered a new starter. One thing i did notice is that there are 2 posts on top of the alternator, one is a ground and one is hot. The ground cable, the visable copper wire coming out of the crimped lug is pretty green, but i tested the resistance on the wire going to the battery and its around .5Ohm. I wouldn't think that would cause it, but i went ahead and ordered a new cable for that to replace it. So maybe it is a ground.

[Booyah45828]

Originally Posted by verotik

I havent ordered a new alternator, i've just ordered a new starter. One thing i did notice is that there are 2 posts on top of the alternator, one is a ground and one is hot. The ground cable, the visable copper wire coming out of the crimped lug is pretty green, but i tested the resistance on the wire going to the battery and its around .5Ohm. I wouldn't think that would cause it, but i went ahead and ordered a new cable for that to replace it. So maybe it is a ground.

An ohm reading really won't tell you much on thicker cables like that. The test to do is a voltage drop test. With the engine running and the alternator loaded as much as you can, measure the voltage between where that lug connects and the negative terminal on the battery. In this situation it's important to have the leads touching clean, corrosion free metal in order to get an accurate reading. I think the spec is something like .2 volts or less, with less being better. You can do a similar thing for the positive cable going from it's lug on the alternator to the battery. You can also do the same thing with the starter motor as well.

That's really the only way to test cables like that.

[roach711]

Check alternator output right at the (clean) alt terminals. If you're getting good voltage there it's time to give the cables a good cleaning. It's a good idea to do that anyway. Look for cables with swelled insulation near the lugs. They can corrode there and the wires get eaten away.

You may also have a weak battery. Most parts stores will do a load test for free but you can check for high battery drain by charging it overnight then disconnecting the charger (and the cables) and letting it sit for a few hours to let it "rest" and lose it's float charge. A fully charged, rested battery should read 12.7v. Then check it again a day later. If you see anything under 12.6v the battery may be going south and need to be replaced.

[Rivetboy]

When replacing a ground cable to the frame, the frame needs to be shiny bare metal between it and the terminal lug and should have an external tooth star washer between them for the best long term conductivity. Then paint the connection with your choice of a corrosion inhibitor.
This is a zero cost solution that works well.
(IMHO)

[verotik]

perfect. I will try these things. Just a weird problem.

[verotik]

So, just a follow up to this problem. I replaced cables and tried everything i could, i was showing 12.2v at the alternator, i gave up and took it to a mechanic. It was equipped with a Penntex 200A alternator. The mechanic had it for a week and never really even looked at it. I have a trip coming up and i need it working, so i got it and took it back home and started thinking about the Penntex sticker, so i googled and within 20 seconds found the Penntex troubleshooting guide. Found the voltage regulator under the air bag blank just where they said it would be, and within just a couple minutes, diagnosed my own problem on the 2nd step as the alternator having a diode problem. Got on ebay, found a new one for $400 and ordered it. That seems pretty damn expensive, but if you get one from an online store, the cheapest i found was $800, and this is one some guy just bought and never used. Put it on and replaced the tensioner at the same time and fired it up, battery light gone and getting 14v off the alternator and at the battery.