My son's 75 is showing a constant 12volt (or amp, I'm not sure which he said) draw on the battery (according to a mechanic friend). Here's the symptoms:

- When the battery was checked, it shows 12v, but it does not have the amps to start the car. What would cause the amps to drain but not the volts?
- Speedometer lights don't work and needle stays at about 20 mph until you get above 40-45 mph, then will go up.
- Tach doesn't work - stuck at about 2300 rpm but will move some when at higher rpms.
- The left turn signal light stays on until I move the lever to the left (for a left turn), then it goes out - no blinking.
- The center gauges were working, but now don't. The fuse was blown and I replaced it, but no help.
- Can start the engine with the battery charged up, but when shut off, usually will not start again; sometimes the ignition just clicks and other times it doesn't make any noise. Changed out the starter - no help.

We did install a SPAL dual fan with a controller which we wired to the hot terminal on the starter and the alternator (per the directions). It is working properly when the engine is running.

I was told it was either a shorted wire or a missing ground. Any ideas what it might be or where I should start looking? I am afraid to take it out since I've had to have it towed back home twice now. I'm not very knowledgeable when it comes to the electrical system, so any help is greatly appreciated.

 

Check EVERY ground you have. Start at the battery, go from there. You can also put a test light between the negative battery terminal and cable. If it lights up, you have a draw, somewhere. Keep the light hooked up, and pull one fuse at a time, until the light goes out. That will, at least, isolate your system that has the draw. Work on that system to find the draw. This will take some time, more than likely, stick with it if it does. You'll find the problem.

 

1 Check and lube cable but could be more than that but this is the first thing to try. Speedo lights - get a test light and see if there is power at the bulb and work backwards from there checkng for power and ground

2 Not sure if 75 a cablt tach? if so, lube cable if electronic may need new board

3 I would check bulb and connector for contact.

4 Use test light and check power and ground

5 check ignition wires at column and make sure they are doing what they need to do with the key. Ignition switch maybe bad. Check grounds also.

My 2 cents worth

 

I'm going to guess that the added current draw from the fans burned out a fuse-link somewhere and the electrical system is back-feeding through some odd feed paths...which is causing your problems. But, that's just a guess....

 

I like the fuse check. Picked up a test light tonight and will give it a try. Hopefully I can narrow down the problem.

 

It won't fix the problem, but it will narrow down to 1 system that you can inspect. That being said, I would also agree with 7T1vette's comments. I think he's on to something that I didn't even think about, good call, 7T1vette.
Your tach is cable driven, your speedo is electronic, You can also disconnect the power and ground to the new SPAL fans you just installed to work backwards.

Good luck, and keep us posted.
BBTank

 

when the switch is on - not the starter or alternator. Then you're on your on from there.

 

I thought 74 was the last year for a cable driven tach and 75 was 1st year for electronic.

 

A possible cause may be the ground strap from the battery to the chassis , if I recall these were made of aluminum wire and corrode internally. Look to see if it's swollen and split, usually under the battery box going to the chassis. It's a quick check .

 

Yes, he just got the two reversed. My speedo is cable and tach is electronic.

 

Question - when I open the door the courtesy lights come on like they should (battery connected). When I put the test light between the negative terminal and the negative cable, the test light comes on, but the courtesy light go out. Shouldn't there still be power going to the lights? Does the tester stop the power going to the system? If so, how will pulling the fuses change anything?

Thanks.

 

The PO replaced the original cable with a new one so it looks good.

 

Also, forgot to mention that when the battery was checked, it shows 12v, but it does not have the amps to start the car. What would cause the amps to drain but not the volts?

 

Now, Thats funny.

 

Now, think about it. Its a 12V battery. It has a certain amount of energy stored in it. It can supply lots of energy in the form of electrical current, at those 12 Volts, for a period of time. That's the definition of power. So just bleeding off some of that power doesn't change the fact that it is a 12V battery. It will still hold that voltage until it is not capable of doing it anymore. But it will still be at 12V, just have no stored energy left. When it is nearly completely depleted, it will start losing the voltage potential.

 

OK, Electrics 101 here, how do the amps come in to play?

 

I thought I just explained it, but lets try something different that you might relate to.

Think about your water hose at your house. It has a certain pressure that it operates at. (Volts). Voltage, is electrical pressure. Now you turn the spigot on. If you just turn it a little there is high resistance to the flow. This is comparable to electrical (resistance). There is little flow (Amps) with high resistance. Amps is the amount of flow. Now you turn it on full blast. The pressure is the same but the resistance is low, so you get a high rate of flow. ( Increased Amps). It will fill your bucket up in a certain amount of time. (Power). That is the measurement of power P= VoltsXAmps.

Most cars are 12V systems. When you operate a device, it is effectively plugged in between the positive post of the battery to ground and introduces a resistance into the circuit that it makes. According to the resistance it has, it will draw a certain amount of current. A starter, by nature draws a bunch of current. It has a low resistance. A battery has to be able to deliver the amps to get that starter to turn the motor. Automotive starters are activated my another device called a solinoid. The solinoid draws a small amount of current to activate the starter. By nature this solinoid will not kick in, if it sees a weak battery. This is what you are experiencing with your car. The battery has been discharged by something else to the point that it is not capable of kicking off the solinoid. Thus the starter seems not to do anything when you turn the key. You need to find what is causing the current draw from the battery. If it is fully charged, It will kick the starter and start the car.

 

Just take it somewhere that has a "Vat40" or comparable tester.
Takes 10 minutes and it will show the state of the alternator, starter and if the battery is still good enough to use. The later units will even give you a printout tape with the specs of each test.

Your battery may well be on it's last legs.

 

That is the clearest explanation anyone has ever given to me. It makes sense now. Thanks for the lesson.

 

Replaced the battery. Just need to find out what is causing the draw on the battery.