i have been dealing with charging system issues on my 780 with a B280. Its obvious that the alternator isn't delivering a charge so just in case,i've ordered a new set of brushes and voltage regulator. However there are a couple of things that have me wondering if it's somthing more simple then that.

First, even with the battery fully charged the gauge on the dash barely climbs out of the red,doesnt seem to be indicating the 13+/- volts that a voltmeter accross the terminals confirms. I assuemd that the gauge was just at fault. However, even when the battery gets REALLY low, 11.5+/- volts, the battery light on the dash NEVER comes on.

When looking though my books, i have found a grounding wire/strap referenced, but i dont see one anywhere near the alternator, so i assume that it grounds through the block? or is this wrong on this motor? Also, i must confess that i can't tell which wire goes to the dash. There are two there, one goes to the oil pressure gauge and one goes to the alternator. Any ideas on how i could test which is which? I have assumed that i have them reversed and swapped them around, but the only difference i can see in the operation of the idiot lights is that with one wire ALL the lights come on, the other way none come on.

Thank you all AGAIN,
Jesse Erickson

My experience is with the 240s, but an alternator is an alternator, methinks.

In the 240s with internal voltage regulator, three wires are necessary:

One large gauge to carry the charging current to the battery, usually via the starter.

One to ground the alternator frame to the block. One the 240 it is black.

One to bring an exitation voltage to the rotor to get charging started. On the 240 this one is red, and is the usual suspect for no-charge situations and warning light problems.

As Mapleleafer said, check the ground wire, as the rubber mount bushings isolate the alternator frame from the block.

Also the belt, an easy check and embarassing when your shop finds it.

The then red wire. It serves several functions.

When the key is on, voltage travels to the instrument cluster warning lights, then to the alternator where it goes through one brush to the rotor windings, then out the other brush to ground. So the warning lights come on, and there is a small current through the rotor windings.

As the alternator begins turning, it begins charging and the charge causes the red wire to get positive polarity. It is the negative polarity that allows the warning lights to come on, so when it is positive the lights go out.

The alt or batt light comes on when the red wire has negative polarity, usually because the alternator has stopped turning.

BUT it can go negative if the red wire is grounded some other way. Such as damaged insulation somewhere, or the attaching terminal falling off. In the case of this illegal grounding, you get a red light that stays on after engine starting, and NO charging.

If the drive belts are OK, trace that red wire. With key on and engine stopped, check for 12 volts at the alternator end. If yes, check the brushes. If no, look for the illegal ground.

Good Luck,

Bob

:>)

Somthing that has me a bit confused is the rubber bushings that both you and Maple mentioned. I dont see any bushings and as fas as i can see there is no room for bushings. I also cant see where a negative terminal might be.

Still stumped,
Jesse

Hey Jesse -

The rubber bushings, on a 240 anyway, are inside the mounting "ears" on the afternator. The long bolt on which the alternator pivots when adjusting the belt tension goes through the bushings, usually called accessory bushings.

On a 240 the same accessory bushings are used on the power steering pump mount and the a/c compressor mounts.

They are hard to see on the alternator, look at the other uses.

Some alternators have a terminal for the ground connection wire some don't, I have seen both ways. Often the alternator end of the wire is connected under one of the alternator frame bolt nuts. The other end is often connected by being caught under one of the bolts holding the alterbator mount onto the block.

I don't know how the B280 alternator mounts, or where. It must be grounded to work.

Hope this helps.

Good Luck,

Bob

:>)

The dash gauge and the warning light are completely separate. You need to check the voltage at the battery. The alternator is mounted on rubberized bushings. There needs to be a ground wire between the alternotor housing and the block.
The wire that triggered all the dash lights is for the alternator.

If you find the charging voltage low at the battery, and the alternator to block ground wire is intact, suspect a loose belt before all else.