This winter I pulled the original AM/FM radio out of my 1970 Roadster. Got the radio back and installed it back into the car. The process required me to pull out the instrument panel (I did not disconnect it just moved it out and to the side) so I could get the radio out. Now that I have it all back together I was driving the other night and when I turned my headlights on I noticed that my turn signals started cycling real slow. Also the head lights started to dim and once I stopped the car and shut it off I could not get the car started. I used a jump box, got it going and brought in home to the garage. It runs great without the headlight on but once I turn them on I get the same results. I have removed the alternator, had it tested and it tested good. I removed the battery and had it tested and it is good (they do a very simple test now that does not include a load test). The car starts fine and runs great. Any thoughts on what I might have disturbed when working on the radio or what else I might check?

 

The first thing I'd check is the battery g
round cable that goes to the frame. Those things are notorious for cause
Ing trouble. Even though you didn't mess with it it is a problem area that should be checked.

 

Make sure your battery cable connections at the battery are CLEAN and TIGHT!!!

I would check and see what the load test on the battery is.

I would then make sure that all connections and terminals at the alternator are GOOD!

I would then test the voltage at the battery when it is running and make sure that it is at least 13.6 volts BUT not more than 16.0 volts 16.0 volts is NOT good and the battery can swell and pop along with destroy electrical components./wiring.

Is your ammeter moving to the (+) side when it is running????....and STAYING on the (+) side when you turn on your headlights, etc.

DUB

 

7t9l82 and DUB,

Thanks for your replies. Last night I got under the car and cleaned up the ground to frame connection. It was already in good condition but I removed the bolt, cleaned the surface and reattached. No change in the situation.

I pulled the starting battery from our boat and tried it in place of my current battery (which is less than one year old) and got the same results. I'm confident the connections to the battery are good (new battery bolts, clean connectors). So I feel I have ruled out the battery being bad.

When I put my volt meter on the battery without the car running it sits at about ~12.8 volts (I keep the battery on a tender when it sits in the garage). Measurement is with the tender disconnected. When I start the car the running battery voltage is ~12.4 volts. That is the same voltage as I get at the terminals of the alternator output (red and ground lug on alternator). When I turn the headlights on the voltage at the alternator drops to ~11.95 V. It went back up to ~12.7 V when I turn the headlights off.

I did a voltage drop measurement between the alternator case and the neg terminal on the battery. It was ~.02 V. I did a voltage drop on measurement between the alternator plus output and the pos terminal on the battery and it was ~.05 V. I concluded from this that the charging path to the battery was good. With this information I was convinced that the alternator was bad so I bought a replacement and installed it. The situation did not change! Ahhhhh.

So any other ideas from the forum?

 

you may have created a short somewhere in your wiring either by pinching a wire or crossing a ground somewhere or you pulled a wire apart when you moved it to the side.

I would try taking apart what you just assemble and try the lights intermittently as you pull wiring apart. Its something that you just did, I doubt it is a coincedence. It could be a ground in your light switch path isnt connected correctly.

the dash/ console lights could be the culprit, just pull the light switch out halfway and see if you have the voltage drop without the headlights.

The radio has a light in it as well thats on your lighting circuit. you could disconnect the readio fully and see what happens, maybe whoever worked on it messed it up internally

 

Your alternator is NOT charging- as Dub said- you should see at least 13.6V when the car is running.

The alternator(s) might not be bad- more than likely it's the wiring TO the alternator.

 

What about the alternator sensing and indicator connections? This is the two wire connection to the alternator and as I understand, the sensing circuit feeds back voltage from the battery positive supply to increase or decrease the charging rate. This should be a red wire going to terminal 2 or F on the alternator. Then there is the monitor circuit connection that as I understand energizes when the ignition switch is turned on does two things, excites the alternator and if you have a warning light (which I don't think is in the car) will light this up if the alternator is not charging. I pulled this off last night and measured 12 volts to ground on one and 0 Volts on the other. Seems there should be 12 Volts on both. Does anybody have any insight on what I should measure here? Thanks.

 

Are the two wires at the alternator inserted correctly and are the connections good?

 

I'm sure they are connected properly as they the connector is keyed and I have not messed with the connector. I'm pretty sure the connections are good. I have moved them around and did not see any change in the alternator output. What should I read for voltage on these two wires. I assume 12 volts on both when running and 12 volts on sensing and 0 volts on field #1 when off?

 

Take it out and have it tested. Cost you zip.

 

Yes! That is correct.
What are your readings?

 

You are on the right track I believe. One wire (red) is the sense wire. the other wire (brown IIRC) is the field wire. Both should have 12 volts with the key on.
Here is a picture of the approx wiring. Check that the alternator light is good. I should be glowing when key is on before you start.

http://www.chargerr.com/Alternators/ALT.HTM

 

This is a 1970 and does not have a GEN light that lights up.

So checking for a dim light is not required on this year model. On that side of the gauge cluster is a HEADLAMP warning light and the DOOR AJAR...BUT this does apply on the later year models that DO have a GEN light.




Red wires at the alternator should be battery voltage when the engine is NOT running and the ignition key does not even need to be in the ignition...and the voltage on these wires should go up IF the alternator is doing its job when it is running.

Keep in mind that these wires (red) do connect to your horn relay on the buss bar that is a part of the horn relay.

The brown wire is 12 volts when the key is ON

I feel your alternator is bad and I know you had it checked.,..but I swear it seems that is is not correct...UNLESS you find a problem in a fusible link somewhere in your wiring.

I DO KNOW that the large 12 gauge RED wire that has the eyelet terminal on it and it is nutted to the alternator stud. You DO want to be careful when messing with that terminal and NOT allow it to spin or rotate due to it can effect the connection INSIDE the alternator.

DUB

 

Yep your right, didn't note the year. Then the amp meter should replace the light in the circuit. Negative before start and positive immediately after if the alternator is functioning.
I'm not sure in what year the voltage regulator became internal in the Corvette. Is the 1970 still externally regulated?

If it's internal and either the sense or the field wire are broken then you should, for testing purposes, be able to attatch the sense to the charge wire (jumper) if that is the one broken and basically make it a one wire ish generator.
Or if it's the field wire that is not live then you should be able to use a jumper and touch the field to the charge wire briefly just to energize the field to get the generator working once the engine is running.

From his testing it appears as if one of those two is not seeing the battery voltage. Seems likely the field wire.

You could also measure the battery voltage at the battery with the lights on. If it's the same or nearly so as at the alternator lug and that is below 12 volts then I would suspect the field wire is not energizing the alternator field and the alternator is not functioning due to this.

 

Thanks for all the help! I'm getting closer. With the key on the field wire does does not have any voltage. I started the car and jumped the field wire to the sense wire and the alternator is putting out 14.6 Volts. So the problem is with the field wire. Now I need to trace it back. Does the field wire go anywhere near the instrument panel? That is what I had move out to remove the radio. Does it connect to the amp meter? I may have knocked the wire loose when messing with the cluster. I have the electrical diagrams but I'm not sure the location of the components in the circuit. You guys are doing great! Thanks for help!

 

Yes, it originates at the ignition switch. Perhaps the connector got knocked loose.

Does your radio work? They are on the same circuit.

 

OK. Lets see if you guys can follow this one. I bought the car last year and shortly after I was experiencing problems starting the car. I diagnosed that the alternator was bad and changed it out. Also all the discharging of the battery killed the battery so I replaced it as well. My view was that I missed diagnosed the alternator when the battery was the problem. I only really drove the car during the day so only on rare occasions did I use the headlights and that was on for a very short period of time. To night when checking the voltages on the sensing and field lines I noticed that the sensing line (per the connection to the alternator) was switching with the ignition switch. Per the wiring diagram this should be connected directly to the battery charging line that is always energized and should not be effected by the ignition switch. That got me curious so I took out the old alternator (I kept it as I think it is the original and I wanted to keep all the original parts) and checked the configuration of the terminals for the sensing and field. They are opposite of that for my new alternator! So, the sensing and field lines were reversed. As it turns out, I have the sensing line that does not have power and that connects direct to the output of the alternator. This is an easy fix as it connect just down stream from the alternator primary output. I now need to decide if I should rewire the connector to work with the new alternator or get an alternator with the right configuration of the terminals. In any case, it appears this problem has been with me for some time, I just have not noticed as I only drove during the day (until this last weekend) and always kept the battery on a battery tender while sitting in the garage. Wow, what a trail of errors. I'm good. Thanks for all your help in leading me with clues to the solution.

 

Yes the amp meter is part of the circuit. It's just above the radio so maybe it got snagged and yanked loose during the radio removal. Either that or it just broke when you moved the panel to the side. Wires do get crispy with age.

 

congrats on figuring it out, that would have been a nightmare if you hadn't kept the original. Good Job!!!

 

Really, the new alternator doesn't have the terminals labelled 1 and 2 in that order (left to right) when looking at it from the back with the terminals facing up? If it doesn't, then that has got to be one crappy knock-off alternator.

Was the connector replaced? I have seen replacement alternator connectors with the 2 wires backwards. Heck, on a similar note I've seen replacement light sockets backwards too, with the brown running the signal filament instead of the tail light filament. Just a lot of shoddy design and product QA these days.

On another note, if you did have the wires reversed and applied constant power to the field (or light or relay) terminal then that would discharge the battery fairly quickly. I wouldn't be surprised if the PO replaces the connector and then had battery draining issues so cut the sense wire wrongly going to the field terminal to stop it from draining the battery.