Long story/ amp lite on

[jlwoods99]

Okay, so today I took the alternator off the truck and took it to Advance Auto, the guy their couldn't figure out how to hook it up took him about 15 minutes to get it to test. Came back ok. So since he had such a hard time I went to another place and he tested it and said nope its definitly bad. So... of to the 3rd parts store and had it retested, I wanted 2 out of 3 voting. A mechanic at the tire store ran it on their machine and told me absolutly its fine. So My batteries are charged to about 14.8 volts but the amp lite comes on still and the volt meter climbs to around 16 volts, what should be my next course of action.

thanks for any suggestions.

jim

 

[jwalterus]

load test while running woulda been my first stop

 

[OLDBULL8]

You can't get 14.8 volts out of a 12 volt battery, unless your charging them with an alternator. Good batteries with no load on them will check 12.5 or 12.6 with a accurate VOM.

You more than likely have an open or shorted diode in the alternator. Alternators are three phase AC volts, diodes change the current to DC voltage, the regulator, regulates between 12.5 to 14.8 VDC.

 

[dgr]

The warning lamp on a ford sits between positive from the alternator and positive from the battery. When the key is on but the engine is not running, power flows from the battery (actually the battery cable), through the lamp to the alternator. Once the engine is running and the alternator field is excited, there should be the same voltage on each side of the lamp. Voltage then stops flowing and the lamp goes out.

The ignition on wire was also used to excite the alternator. They put a resistor in parallel to the lamp so the alternator would still get excited if the bulb went out. This is just noise for the problem you seem to be having.

If you have a warning lamp turning on, power must be flowing through it. I would assume it's the alt/reg combo most of the time.

How long did it take you to go to three parts stores and get your alternator tested? I think that 3G regulator is about $20 at any part store.

 

[jlwoods99]

45 minutes at the most. I'll get the son in law on this as he understands the electrical stuff ya'll mentioned. So with that being said we'll perform some tests and I'll be back!

jim