Ammeter & Alternator wiring questions

snakebyt · #1 (**permalink**) 08-29-2003, 08:21 AM

I have a Contemporary with a Ford 351W that the ammeter has never worked on. In their instructions they said to bridge the A & S terminals on the voltage regulator. Would that prevent the gauge and warning light from working? I do have the alternator stator connected to the S terminal on the regulator. There are no other charging issues; the car cranks well and starts whenever I get in to it.

TIA

Tom

Clois Harlan · #2 (**permalink**) 08-29-2003, 09:46 AM

Tom,

I had a similar problem about 4 years ago when I built my Cobra. After becomming completely frustrated I took my alternator back to AutoZone and traded it for one with a built in regulator (I think it cost about $50 for a 70 amp). Now everything works great.

Good luck,

Clois

Bob Putnam · #3 (**permalink**) 08-29-2003, 10:12 AM

The warning light will only work with the layout on the right. If the basic wiring layout is OK, the ammeter should work with either regulator setup.

If you disconnect the wires at the ammeter, everything should be dead.

snakebyt · #4 (**permalink**) 08-29-2003, 05:13 PM

Thanks for the info Bob. Is there any way to test the ammeter at home?

TIA
Tom

Bob Putnam · #5 (**permalink**) 08-30-2003, 04:32 AM

Tom,

If you're not getting any reaction when you turn the headlights on (or better still, the fan), either the ammeter is defective or it's wired incorrectly.

PatBuckley · #6 (**permalink**) 08-30-2003, 05:43 AM

A simple test I have been told about is to put a screwdriver to the back center of the alternator - if it is magnetic the alternator is working.

I have yet to run into a bad alternator so I have never been able to "prove" this.

Steve R · #7 (**permalink**) 08-31-2003, 08:04 PM

Pat,
Damn, I never thought of that. Makes perfect sense as an energized field winding is a big magnet.
I'm gonna go out and try it.

Steve

snakebyt · #8 (**permalink**) 09-04-2003, 07:04 PM

Bob,

You've been so helpful about this. Can I ask you for more troubleshooting advice? I have the warning light wired as you described but it still doesn't light up when I turn the key. I can get it to light up if I connect my test light to the I terminal on the voltage regulator plug and ground it. I also have 12v at the A terminal. So it seems like I'm missing a ground connection somewhere. There are 2 terminals on the back of my alternator that have no markings. Do these need to be grounded?

Thanks
Tom

Bob Putnam · #9 (**permalink**) 09-05-2003, 04:02 AM

Snakebyt,

The alternator needs to be grounded some way, but this is usually done automatically if it's mounted to the engine without insulators. I use a "redundant" ground wire to an alternator stud just in case other grounds have corrosion.

Make sure that the voltage regulator is grounded too.

snakebyt · #10 (**permalink**) 09-25-2003, 05:16 PM

The problem turned out to be the voltage regulator. $9.95 (+ $8 Shipping and Handling!) to JC Whitney fixed it all. The light lights, the needle moves, it's a beautiful thing. Thanks to everyone who answered.

Tom