alternator test?.... without ER visit

[74w300uteline]

74 360 4 speed has been having starting problems. I'm constantly charging and swapping batteries. is it possible to verify a running alernator output without killing/electrocuting my self. I tested wiring for a batterydrain/leak none found.

[712edf]

Yes. It involves having a multimeter & possibly a manual telling you what to test. I off hand don't know the exact procedures.
Bucky

[QuantumJo]

I would think all that you have to do is get it running, turn on everything that is electric (lights, blower motor, wipers ect...) then put a volt meter across the batt. you should see about 14v if it is working properly.

[OLD DODGE]

QJo is right. You should see close to 13 volts at the battery when the engine is not running, and close to 14 volts when it is.

[Andyp]

I was told once that, get it running,turn everything on, disconect 1 battery lead and if it dies, it's your altenator that's the problem.
just my 2 cents

[712edf]

I was told once that, get it running,turn everything on, disconect 1 battery lead and if it dies, it's your altenator that's the problem.
just my 2 cents

I do it the same way, but have everything OFF! Even if it dies that doesn't isolate the alternator itself as the problem. Still could be regulator or wiring.

Bucky

[74w300uteline]

thanks all

I like the Idea of testing across the batt terminals, looking for a difference running/ nonrunning. I can wrap my head around the theory behind it.
The reason i asked was for safety. I have no automotive background but I'm becoming more involved as time goes on. safety things you all take for granted, I may not know. loose sleeves around fans, opening radiator caps hot, and I thought i remembered something about not touching wires.
Maybe it was spark plug wires?

[712edf]

Definately don't mess with spark plug wires.....that's secondary voltage from coil, much higher.
bucky

[Don Williams]

The surest way to test the alternator output is to measure the current with a DC ammeter. Test the big wire (not the small field wires) where it comes out of the alternator before any splices/branches in the circuit. That way you are reading the full output of the alternator as the current will divide between the different paths depending on what loads are turned on. Have the truck running and turn on the headlights and heater blower motor to put a good load on the system. I would expect to read around 20-30 amps on the meter. You can also increase and decrease the engine speed and you should see a change in the alternator output.

A clamp-on style meter is the easiest to use but they are expensive so do that only if you can borrow one. Remember it must read DC amperes. Harbor Freight sells an in dash ammeter for about $5 and that could be spliced into the line temporarily to read the current.

You could also remove the alternator and take it to a parts store to have them bench test it. I did have one alternator check good on two different bench machines and still not work in the truck. Put on a new regulator and it still wouldn't work in the truck. Put in a new alternator and its been working for 2 years. Can't explain that one.

[KRB64]

...You could also remove the alternator and take it to a parts store to have them bench test it. I did have one alternator check good on two different bench machines and still not work in the truck. Put on a new regulator and it still wouldn't work in the truck. Put in a new alternator and its been working for 2 years. Can't explain that one.

With no automotive background, this is the simplist and easiest but make sure the bench guy knows what he is doing. Preferably find one with gray hair and bifocals.

On the other hand this is a good place to start your shadetree mechanicing. Get a service manual and some basic tools and start trouble shooting. Will make you feel more secure when driving (knowing you can fix on the fly if necessary).

But like stated before, stay away from the plug wires and coil - that stuff will hurt unless done correctly... so I've heard... :) Another caution is to be aware of sparking near the battery - especially if its charging or recently been charged...

[Gordon Maney]

If you have a battery charger, charge your battery completely, or as best as you can determine.

Do not disconnect the battery with the engine running. You are running the alternator on an open circuit and that is bad for it.

Connect a voltmeter, as an earlier post said, to the battery terminals as the engine is running. Take your reading with no accessories on at idle, and a bit above, to see if voltage rises appreciably.

As stated earlier, it should be about 14 volts. The manufacturer's spec on a Chrysler product historically was 13.5 to 14.5 volts.

[74w300uteline]

results

12.06 running 12.25 off... 12.36 after 3 min off.

[OLD DODGE]

12.06 running 12.25 off... 12.36 after 3 min off.

NOT charging!

[712edf]

NOT charging!

Yep......if runnnig voltage is lower than static voltage than there is an issue. Welcome to the world of Dodge electric mayhem.

Bucky

[74w300uteline]

4 wires leaving Alternator

1- black thick, ground to alternator/block bracket
2- red thin, to borg warner voltage regulator on center firewall
3- lime green thin, to borg warner voltage regulator on center firewall
4- black thick, connects to alt with right angle boot type connector.
I'm wondering if during my Dilectric grease binge (2 months ago) i reversed the red and green slide on connectors. I tried to stare and compare with my other 74 360 but the fire truck has a much bigger alternator and the connection points are not similarly located. perhaps i fried the voltage regulator? what symptoms would result from reversing the red and green wires? instant failure (smoke and sparks ) or ?