Dim alternator #1

[carctruck]

So Here I am yet again with alternator questions (sorry guys). In the process of rebuilding my #1 alt (as the #1 gen light was dimly lit and getting brighter as I increased the load) I noticed that the case to my alternator was cracked pretty severely, so I put in on my shelf as benchstock parts and bought another alternator (1975 caddy deville alternator) I crosschecked the part numbers and its the correct alternator, however I still get a #1gen light dimly lit and brighter as I increase the load, any thoughts?

 

[lnnayers]

a dim light is usually indicative of a bad diode, either in the diode trio or the rectifier bridge. [alternators generate ac voltage and the diodes correct or alter the output to be dc voltage]

 

[Barrman]

Since you have evidence of a bad alternator, swapped in a good one and the problem is the same. Maybe you have a short on the truck side of the system and it is causing your alternators to go bad. Check your voltage at the plug with the engine off and on.

 

[carctruck]

Thats what I thought but I checked all grounds (to the best of my knowledge) voltage seems to be good on/off, Im planning on tracing hot wires tonight for shorts.

 

[Barrman]

There are several threads about what to do. Basically, unplug the alternator, check the voltage at the plug with the key off and on. If they all have 12 volts with the key on and the plug off, then the truck side is probably good and you are back to testing the alternator.

 

[68impalass]

I would check the heater fuse circuit. does the light get brighter with the fan on?

 

[carctruck]

actually yes, is the primary load that brightens the light, it would make sense if there were a short somewhere before the fan on/off switch.

 

[68impalass]

it could be a bad connection at the heater fuse. Check the contacts at that point.