74 Electrical Problem
Thread Starter
Burning Brakes
Joined: Mar 2010
Posts: 803
Likes: 4
From: Christchurch, New Zealand
74 Electrical Problem
So anyway, driving home at night, and the tach instrument lights dim, and the right turn indicator light glows. The indicators won't work. As I keep driving, the headlights get dimmer, and the car starts to die. First time it happened, I had just pulled into the garage. I got lucky. It happened a few other times, and I could fix it by dimming the instrument lights and bringing them up again, and once, I stopped it by using the indicators. But last night, I had to pick my daughter up, and it started to happen again. The only way I could keep the car going to get home, was to shut the lights off. All of them, as I tried to drive with just the park lights only. No good.
I pulled the drivers side lower dash to see what was happening back there, and I'm not 100% sure, but it looked like the ground plug for the tach was off, and the arch shaped connector between the two gauges was only held on with one screw on the speedo side. The headlight switch is brand new, fwiw. The quake damaged roads are pretty tough on the old girl, but I really enjoy driving her! Anybody have any ideas why the battery would be draining so badly?
I pulled the drivers side lower dash to see what was happening back there, and I'm not 100% sure, but it looked like the ground plug for the tach was off, and the arch shaped connector between the two gauges was only held on with one screw on the speedo side. The headlight switch is brand new, fwiw. The quake damaged roads are pretty tough on the old girl, but I really enjoy driving her! Anybody have any ideas why the battery would be draining so badly?
Thread Starter
Burning Brakes
Joined: Mar 2010
Posts: 803
Likes: 4
From: Christchurch, New Zealand
Will do. Thanks Scott.
But if it's the alternator, why would it only be an issue when the lights are on? Lights drawing too much current for the reduced alternator output? Heater and radio work fine. And wipers. I would have thought it would be a short somewhere. I'll test the alternator when I get home tonight.
But if it's the alternator, why would it only be an issue when the lights are on? Lights drawing too much current for the reduced alternator output? Heater and radio work fine. And wipers. I would have thought it would be a short somewhere. I'll test the alternator when I get home tonight.
Last edited by mrmagrath; Jul 29, 2013 at 09:29 PM.
Le Mans Master
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From: mount holly NC
2025 c3 ('74-'82) of the Year Finalist - Unmodified
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I agree, start with checking the alternator and fully charge the battery.
Did the alternator put out so much power that it killed the battery?
After that you might want to look at the new light switch.
Did the alternator put out so much power that it killed the battery?
After that you might want to look at the new light switch.
Thread Starter
Burning Brakes
Joined: Mar 2010
Posts: 803
Likes: 4
From: Christchurch, New Zealand
Battery is charged. I'll test the alternator output tonight. Thanks Pete. How do you explain the tach lights dimming, and the right indicator arrow light glowing? And the indicators not working when that happens? It's got me beat for the time being!!!
Le Mans Master
Joined: Aug 2006
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From: mount holly NC
2025 c3 ('74-'82) of the Year Finalist - Unmodified
2019 C3 of Year Finalist (appearance mods)
What was the reason you changed the light switch?
Take a close look at the rheostat in the new headlight switch.
I'm sure others will help too.
Thread Starter
Burning Brakes
Joined: Mar 2010
Posts: 803
Likes: 4
From: Christchurch, New Zealand
Cheers Pete.
The reason I changed out the switch, was that I lost the instrument lights, and the rheostat never worked on the old switch as well. The instrument lights would work with the park lights but not the headlights. I've just been searching the forum for any clues. It's about all I can do right now (I'm at work! Shhh!).
As an aside, the original radio keeps blowing fuses too.
The reason I changed out the switch, was that I lost the instrument lights, and the rheostat never worked on the old switch as well. The instrument lights would work with the park lights but not the headlights. I've just been searching the forum for any clues. It's about all I can do right now (I'm at work! Shhh!).
As an aside, the original radio keeps blowing fuses too.
Thread Starter
Burning Brakes
Joined: Mar 2010
Posts: 803
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From: Christchurch, New Zealand
http://forums.corvetteforum.com/c3-t...lights-on.html
This pretty much explains the weird indicator light issue. As I said above, the tach ground was hanging off, and the arch one between the two gauges at the top was loose.
Now, to find out why the battery's draining when the lights are on. Or maybe that's it?
This pretty much explains the weird indicator light issue. As I said above, the tach ground was hanging off, and the arch one between the two gauges at the top was loose.
Now, to find out why the battery's draining when the lights are on. Or maybe that's it?
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Le Mans Master
Joined: Aug 2006
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From: mount holly NC
2025 c3 ('74-'82) of the Year Finalist - Unmodified
2019 C3 of Year Finalist (appearance mods)
The link you posted has some good suggestions. try that .
Here's the ground connections for the tach - speedometer and the harness.
I don't see the "Arch" but if you have it, connect it.
Here's the ground connections for the tach - speedometer and the harness.
I don't see the "Arch" but if you have it, connect it.
Thread Starter
Burning Brakes
Joined: Mar 2010
Posts: 803
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From: Christchurch, New Zealand
I really appreciate your help Pete!
The "arch" is an arc shaped piece of steel that goes between the two gauge bezel screws at the top of the gauges. Got it from either my 75 or 76 parts car. I guess it's a backup ground. The grounds were connected, but with the bumpy roads here, I reckon the tach one must have vibrated off. I'll reassemble everything, making sure the grounds are on good, and see what happens. I'll still test the alternator as well. While I'm at it, I'll put the tach cable on, ready for when I get a tach drive HEI. My birthday's coming up!!
The "arch" is an arc shaped piece of steel that goes between the two gauge bezel screws at the top of the gauges. Got it from either my 75 or 76 parts car. I guess it's a backup ground. The grounds were connected, but with the bumpy roads here, I reckon the tach one must have vibrated off. I'll reassemble everything, making sure the grounds are on good, and see what happens. I'll still test the alternator as well. While I'm at it, I'll put the tach cable on, ready for when I get a tach drive HEI. My birthday's coming up!!
Thread Starter
Burning Brakes
Joined: Mar 2010
Posts: 803
Likes: 4
From: Christchurch, New Zealand
Put the multimeter across the alternator. Got about 12.4-6v. Turned lights on, and that dropped to 11.5v. Tested the battery with engine off. 13v. Turned lights on, and watched the voltage drop rapidly. So, short in the light circuit somewhere?
Last edited by mrmagrath; Jul 30, 2013 at 05:10 PM.
Melting Slicks
Joined: Mar 2007
Posts: 2,520
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From: Hinckley OH
The alternator output should be 14 volts or somewhere close to that. I would take it off and have it tested at a parts store just to confirm that it's bad. I think you just solved your problem. I just had mine fail and the gauge in the car didn't show a discharge unless I turned the lights on ... you would think it would show a discharge with the engine running but it doesn't.
Last edited by my 76 ray; Jul 30, 2013 at 08:20 PM.
Thread Starter
Burning Brakes
Joined: Mar 2010
Posts: 803
Likes: 4
From: Christchurch, New Zealand
The alternator output should be 14 volts or somewhere close to that. I would take it off and have it tested at a parts store just to confirm that it's bad. I think you just solved your problem. I just had mine fail and the gauge in the car didn't show a discharge unless I turned the lights on ... you would think it would show a discharge with the engine running but it doesn't.