79 with zero voltage from alterator?
Melting Slicks
Joined: Oct 2006
Posts: 2,417
Likes: 336
From: Texas
looks like it originates at the (batt. light) , its a brown wire on my 79, you can see it in this diag. on the right.
http://www.corvetteforum.net/c3/tune...l/index8.shtml
http://www.corvetteforum.net/c3/tune...l/index8.shtml
Team Owner
Joined: Aug 2006
Posts: 24,125
Likes: 15
From: Columbia Missouri
Correct, three wires with same voltage with car running-key on. Turn off and no volts on third wire. Voltage on fusable links on starter. Still alt not performing-zero. Electrically whole car works. It has got to be something with that signal wire. how can I mimic the signal to turn on the alt? Where actually does that signal wire originate?
Thanks
Thanks
I have a feeling the problem is going to be in the heavy gauge red wire that runs from the BAT terminal of the alternator to the starter. In your first post you say you get 0 voltage at the BAT lug. That lug should ALWAYS have the same voltage as the battery. Test that BAT lug at the alternator and run that number against the voltage at both the starter and at the battery. They are all connected. If it truly has 0 voltage then the problem would be that heavy gauge red wire, which is also a fusible link.
Team Owner
Joined: Aug 2006
Posts: 24,125
Likes: 15
From: Columbia Missouri
Best I can determine, the brown wire traces from the alternator plug, to through the bulkhead connector, and into the gauge cluster harness, where it meets the GEN light bulb. The other side of that bulb gets the same switched 12V source that all the other gauges get, from the main harness.
I'm getting confused looking at the wiring to see where the gauge cluster gets it's source, which would be the fuse panel. The problem is I am looking at a '77 AIM, and my fuse panel is different than yours. I have glass fuses and you should have plastic.
Thread Starter
Racer
Joined: Mar 2005
Posts: 285
Likes: 0
From: Keller Texas
Took bottom of wire harness by starter off to check fusable links-no resistance.
Took light bulb connected to brown wire and hot on fuse box trying to start alt-no go
Took alt back to autozone-alt passed twice
Took light bulb connected to brown wire and hot on fuse box trying to start alt-no go
Took alt back to autozone-alt passed twice
Team Owner
Joined: Aug 2006
Posts: 24,125
Likes: 15
From: Columbia Missouri
Thread Starter
Racer
Joined: Mar 2005
Posts: 285
Likes: 0
From: Keller Texas
What does the alt resister wire do-cut down volts or ohms?-took ohm reading on my wire-500ohms-is this correct? heard there should be only 3 v going to alt from Street and Performance?
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Team Owner
Joined: Aug 2006
Posts: 24,125
Likes: 15
From: Columbia Missouri
The resistance should be between 35 and 350 OHMs if I recall correctly. I think 500 is too high, and that might be part of your problem.
Having 3V would be far too low. The 12V to the alt via the brown wire is simply just a switched 12V from the IGN circuit.
Racer
Joined: Feb 2009
Posts: 427
Likes: 49
From: Pgh. Pa.
DB is right about the alt bat post. Must have battery voltage there with key on or off. This still sounds like the problem to me and not the lite wire. Is the alt grounded? You can get a deceptive reading using an ohm meter to test the fuse link. They often break inside the insulation and if they are even barely touching inside the wire you will still get a good read with a ohm or even a volt test but it won't carry amperage. Just moving it is enough to make a contact. Pull on the fuse link and if it stretches it is bad. To test if the bat wire is the problem run a jumper wire from alt bat post to starter post or battery pos terminal and see if voltage increases when car is running. Make sure alt is grounded even if you have to run a jumper there too, just to be sure.
