Expert: Kevin Pilotte - 7/29/2009

Question
QUESTION: Hi Kevin,

Had a couple of interesting problems yesterday upon driving my car (’68 AMX) and wondered what your thoughts were.

First, I have a rebuilt alternator installed, belt tension is good, and trickle-charger charges the battery when the car isn’t being driven.

Yesterday, upon running the engine, alt. light came on (bright alt. light) and gas gauge dropped to ½ full (tank was previously full).  So, I checked alt. connections  and one wire was off—reconnected and tried again to run the engine. Alt. light on again and gas gauge needle again dropped to ½.  I checked my TSM and there’s no wire connection at all bet. the alt. and gas gauge—that’s puzzling!

After driving away, alt. light goes out and gas gauge returns to normal.  Now, I can’t turn the engine off, no matter which way the key is turned.

Arrived at cruise night and parked the car.  Later on in the evening, started the vehicle.  Alt. light comes on (bright alt. light), gas gauge needle drops below gas level once again, and after driving the vehicle away, alt. light goes off.  Still wasn’t able to turn engine off with ignition key.  So, do I have a defective ignition switch? What about the alt. light?

Thanks,

Steve

ANSWER: Some possible areas that might cause this:
1) Alternator diode trio
2) CVR on speedo circuit board
3) Shorted ignition switch.
4) defective alternator

---------- FOLLOW-UP ----------

QUESTION: Kevin,

What is "CVR?"

Answer
Sorry,
Constant Voltage Regulator. It's a small component plugged into the back of the printed circuit board. It controls tha voltage to the gauges. It can cause the gauges to act up or not work at all.
Go to page 34:
http://www.oldcarmanualproject.com/manuals/AMC/1973/Service/Part1/Chapter3html/b