1980 battery light
Burning Brakes
Joined: Jan 2012
Posts: 943
Likes: 73
Burning Brakes
Joined: Jan 2012
Posts: 943
Likes: 73
While your checking, see what the voltage is to the brown wire on the alternator plug. It will be the wire from the ignition switch with the battery light in the circuit. Check it with the key on. There are only 2 wires in the plug, the smaller diameter wire is from the ignition. I am at work now so I can't run out to the garage to check the color.
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Thread Starter
Racer
Joined: Mar 2012
Posts: 353
Likes: 3
From: cincinnati oh
well, the alternator voltage reads at 14 at the battery. the voltage at the alternator reads 14. ran a ground from alternator to frame, light stays on more dim now. could it be a bad ground from battery to frame?
Burning Brakes
Joined: Jan 2012
Posts: 943
Likes: 73
With 14volts, the alternator is putting out pressure, it would be nice to know how much amperage was flowing. Any chance to borrow a clamp type ampmeter?
Did this problem just start?
It would be nice if some other members jumped in with troubleshooting suggestions.
Le Mans Master
Joined: Mar 2004
Posts: 7,454
Likes: 1,480
From: Little Rock AR
I would tear down alternator to check "diode trio" with ohm meter. Small chip looking thing. Needs to have continuity in only one direction. If continuity flows both ways, you need to replace diode trio. Cheap and easy fix.
Diode bridge is different and is used to generate power to recharge battery. Diode bridge is larger rectangular heat sink looking thing with 3 studs wires and nuts... but I bet it is working fine as you have plenty of running voltage.
Diode trio only functions to light the dash light when alternator is not charging... and yours IS charging when engine is running so it works fine.
You have current flowing thru that circuit one way or another.
Diode bridge is different and is used to generate power to recharge battery. Diode bridge is larger rectangular heat sink looking thing with 3 studs wires and nuts... but I bet it is working fine as you have plenty of running voltage.
Diode trio only functions to light the dash light when alternator is not charging... and yours IS charging when engine is running so it works fine.
You have current flowing thru that circuit one way or another.
Le Mans Master
Joined: Jan 2006
Posts: 9,192
Likes: 27
From: Boca Raton Florida
So you changed the underhood wiring....first clue
unplug the 2 wire connector from the alternator, does the light still come on? If so you ave a wiring issue. The light is powered in the dash circuit and the ground side of the lamp provides voltage sensing. If the sense side of the alternator fails it will turn on the light.
unplug the 2 wire connector from the alternator, does the light still come on? If so you ave a wiring issue. The light is powered in the dash circuit and the ground side of the lamp provides voltage sensing. If the sense side of the alternator fails it will turn on the light.