Charging System Question

[1badTTA]

This isn't TR specific but it is the same setup as a TR. What are proper readings for Ohms and voltages for the Alternator to function correctly. The alt light is sighting up all the time and the alternator checks fine on a bench but isn't putting out much of anything in the car. I get 12.00v with the engine running and when I unplug the alternator it drops to 11.8v and slowly drops as it drains the battery. I know there is something to do with a resistance in a wire and the Alt light but don't know which wires to check and what the readings should be. Someone has had this problem before so please help me out as it is driving me nuts!!

[HairDrier]

I dont know the proper readings but it just sounds like a regulator problem to me

[zbuickman]

Yes if your alt light burns out you will lose the stator field, rendoring the alt useless. how ever that does not seem to be the case with yours. it sounds as though the regulator took a :as:

[1badTTA]

I dont know the proper readings but it just sounds like a regulator problem to me
Well I wish it was that simple, but the alternator works fine on the test bench and a different alternator also did the same thing on the car. Also, the Volt light has always been on rather dim and lately it has gotton brighter. That is why I am almost positive it has to do with the wiring. Basically what I need is a caspers "Field Fix" kit that will plug into a '78 Olds Starfire and I would be in bussiness:deal:

[HairDrier]

First thing I would do is check all grounds make sure they are clean and tight. If you have a hotwire check that connection also, maybe it is corroded

[Steve Hughes]

First thing to check is the voltage at the alternator. If it's higher than the battery voltage the battery feed wire probably has a problem. If that's the case put one lead of your volt meter on the hot terminal on the alt and the other on the positive battery post with the car running. What is the voltage drop? Shouldn't be much over about .4 volts. If that checks ok do the same on the ground side. From the alt case to the negetive battery post. What's the voltage drop there? If voltage is the same at the alt as it is at the battery then unplug the connector at the alt and run a wire directly from the battery to the terminal on the alt.

[TurboJim]

Actually, the first thing to check is that the batt light in the dash works. Then we check for voltage drop from the lug on back of the alt to the pos batt terminal, then from alt case to neg batt term. All voltage drops should be under .1v with the circuit LOADED (ie: engine running) Any circuit with .5 volts or more is considered BAD. If all circuits check out, its alternator time.

[1badTTA]

Actually, the first thing to check is that the batt light in the dash works. Then we check for voltage drop from the lug on back of the alt to the pos batt terminal, then from alt case to neg batt term. All voltage drops should be under .1v with the circuit LOADED (ie: engine running) Any circuit with .5 volts or more is considered BAD. If all circuits check out, its alternator time.
Thanks Jim, all the voltage drop checks turned out to be less than .1vdc so either the field isn't completeing the circuit or the alternator is bad (actually both are). I will probably just run out and buy a rebuilt one and return it if it doesn't work.