viper 5704 comm issue

Are those measurments in the key off position with the battery connected? Also check for key off voltage on the outputs from the key switch. Based on the Ohms on the Ingition and ACC posts would lead me to believe one or both has a ground issue. AKA common ground.

What is the battery voltage when the car is running?Kevin Pierson

KPierson wrote: What is the battery voltage when the car is running?

Yes, that is with key off and battery connected. This is Factory Five MK4 roadster (65 cobra. I am running a Ron Francis harness + EFI harness for engine. The vehicle is charging properly and I have tested comm with and without alternator connected during engine ON. Thanks guys

I am going to start by pulling fuses and retesting continuity to see if I can narrow down the leak.

The higher resistence on the ingnition and ACC would be a poor connection on the (+) or bad ground. As you increase flow or load the resistence will go up. Try checking the resistence under load on the circuits. But I would start with the ground side of the Ron Francis harness. As the higher ohms on both circuits has to be a common issue.

I don't think you have an issue with your ignition wiring. If you connected the alarm directly to the battery like you stated you did and the system didn't work while the car was running the ignition switch would be ruled out. I'm not sure how the +12 is measuring 0 ohms to ground, but I wouldn't be surprised to see the ACC or IGN within 20 ohms to ground with the key off - these wires typically rest at ground when the key is off. At this point I would expect a voltage level issue (ie too much voltage or too little voltage while the car is running) or a very noisy DC ground level that may be impossible to diagnose without an oscilloscope. The ignition system would still be my #1 suspect for noise as the high voltage and high frequency can create all sorts of noise issues. It may be beneficial to put a very large cap (like a 1F) right at the alarm and see if anything changes. This will level voltage and can smooth out any ripple. However, it won't fix voltage level issues. What is the battery voltage while the car is running? Kevin Pierson

KPierson wrote: I don't think you have an issue with your ignition wiring. If you connected the alarm directly to the battery like you stated you did and the system didn't work while the car was running the ignition switch would be ruled out. I'm not sure how the +12 is measuring 0 ohms to ground, but I wouldn't be surprised to see the ACC or IGN within 20 ohms to ground with the key off - these wires typically rest at ground when the key is off. At this point I would expect a voltage level issue (ie too much voltage or too little voltage while the car is running) or a very noisy DC ground level that may be impossible to diagnose without an oscilloscope. The ignition system would still be my #1 suspect for noise as the high voltage and high frequency can create all sorts of noise issues. It may be beneficial to put a very large cap (like a 1F) right at the alarm and see if anything changes. This will level voltage and can smooth out any ripple. However, it won't fix voltage level issues. What is the battery voltage while the car is running?

He has tried 2 different ignitions systems and the same issue. He has checked the voltage when running and it tested good. The number 1 cause of noisy grounds is a poor connection to ground. If you have a poor connection on ground you will loose amps/current not volts under load, due to resistence which can cause a noisy dc system. Can even cause noise in radio reception, like whine. 20 ohms no load will multiply as load increases on a poor connection. I have never seen a Ignition or ACC have that high of resistence and work properly. They usually have 3 to 4 ohms max on feed circuit wires of this kind.

Poor RFI shielding on the ignition/injection system? Bad alternator ground? Bad, poor or lack of engine to body work to battery grounds?

lurch228 wrote: KPierson wrote: I don't think you have an issue with your ignition wiring. If you connected the alarm directly to the battery like you stated you did and the system didn't work while the car was running the ignition switch would be ruled out. I'm not sure how the +12 is measuring 0 ohms to ground, but I wouldn't be surprised to see the ACC or IGN within 20 ohms to ground with the key off - these wires typically rest at ground when the key is off. At this point I would expect a voltage level issue (ie too much voltage or too little voltage while the car is running) or a very noisy DC ground level that may be impossible to diagnose without an oscilloscope. The ignition system would still be my #1 suspect for noise as the high voltage and high frequency can create all sorts of noise issues. It may be beneficial to put a very large cap (like a 1F) right at the alarm and see if anything changes. This will level voltage and can smooth out any ripple. However, it won't fix voltage level issues. What is the battery voltage while the car is running? He has tried 2 different ignitions systems and the same issue. He has checked the voltage when running and it tested good. The number 1 cause of noisy grounds is a poor connection to ground. If you have a poor connection on ground you will loose amps/current not volts under load, due to resistence which can cause a noisy dc system. Can even cause noise in radio reception, like whine. 20 ohms no load will multiply as load increases on a poor connection. I have never seen a Ignition or ACC have that high of resistence and work properly. They usually have 3 to 4 ohms max on feed circuit wires of this kind.

But if he connected the system directly to the battery that would rule out a bad in car ground. If the poor ground was a chassis ground and he chassis grounded the system I could see there being a problem. But, if he connected the system directly to the battery a poor chassis ground shouldn't affect anything. It's definitely an interesting case and something I've never seen or heard of before. Also, he has not posted what the voltage is at running, just that he checked it. I am curious if the voltage is right at 14.4vdc or higher or lower.Kevin Pierson

KPierson wrote: lurch228 wrote: KPierson wrote: I don't think you have an issue with your ignition wiring. If you connected the alarm directly to the battery like you stated you did and the system didn't work while the car was running the ignition switch would be ruled out. I'm not sure how the +12 is measuring 0 ohms to ground, but I wouldn't be surprised to see the ACC or IGN within 20 ohms to ground with the key off - these wires typically rest at ground when the key is off. At this point I would expect a voltage level issue (ie too much voltage or too little voltage while the car is running) or a very noisy DC ground level that may be impossible to diagnose without an oscilloscope. The ignition system would still be my #1 suspect for noise as the high voltage and high frequency can create all sorts of noise issues. It may be beneficial to put a very large cap (like a 1F) right at the alarm and see if anything changes. This will level voltage and can smooth out any ripple. However, it won't fix voltage level issues. What is the battery voltage while the car is running? He has tried 2 different ignitions systems and the same issue. He has checked the voltage when running and it tested good. The number 1 cause of noisy grounds is a poor connection to ground. If you have a poor connection on ground you will loose amps/current not volts under load, due to resistence which can cause a noisy dc system. Can even cause noise in radio reception, like whine. 20 ohms no load will multiply as load increases on a poor connection. I have never seen a Ignition or ACC have that high of resistence and work properly. They usually have 3 to 4 ohms max on feed circuit wires of this kind. But if he connected the system directly to the battery that would rule out a bad in car ground. If the poor ground was a chassis ground and he chassis grounded the system I could see there being a problem. But, if he connected the system directly to the battery a poor chassis ground shouldn't affect anything. It's definitely an interesting case and something I've never seen or heard of before. Also, he has not posted what the voltage is at running, just that he checked it. I am curious if the voltage is right at 14.4vdc or higher or lower.

Guys thanks for yalls help. Though I know it is an interesting case, that may not be my first choice of words for this road block.    I will put the DMM on the battery while running and off and post results. I know the gauge was reading right around 14, but the precision of that is purely for go/no go on charging. The ground for the alternator is created by the mounting bolt, there is no cable or strap to engine. I will post some pictures today of the overall set up so everyone can visualize a little better what I am working with.