Low voltage from lighter
 

I got one of those volt meters that plugs into the lighter. It reads low, 10.5 or 11.0 when I rev the engine past 2K rpm. Using a volt meter, the battery reads 12.76 and the lighter voltmeter reads 12.8. I also ran the meter in my other car and get the same 12.1 and around 14 when I rev the engine. I just reinstalled a nos lighter and cleaned all the contacts. In the springtime I removed all of the fuses and cleaned all the contacts so I bet they are ok. Any ideas about this low voltage? Where does the power for the lighter come from? BTW, I don't have any issues with my charging system, it was checked at my last oil change about a month ago and the charging light goes off when I start the car.
thanks

http://forums.pelicanparts.com/uploa...1535734075.JPG
http://forums.pelicanparts.com/uploa...1535734075.JPG
http://forums.pelicanparts.com/uploa...1535734075.JPG

Was the battery voltage measured with the engine running? If the engine was off, 12.8 volts is good. With the engine running, 12.8 volts means your charging system needs repair. Normal engine running voltage should be around 14 volts.

If you test at the battery terminals with the engine running what how many volts do you get? That should confirm the condition of your alternator. I'd check the big grounds too to make sure they are clean and tight.

check the resistance from the lighter hot wire to where ever it terminates, removing the connection first, the wire might be the problem (providing the battery is good and the alt. is charging to 14 volts) there might be other issues with the alt. Also, check that the lighter gage is reading correct voltage vs a calibrated meter.

Maybe your voltmeter is inaccurate. Take a multimeter and test the cigarette lighter receptacle itself... I think the plug in voltmeter is inaccurate or the connection to the receptacle is faulty. Don't short the line when checking the receptacle...

I used a multimeter and I got 12.6 volts from the battery and 14.2 volts with the car running at about 2400 rpm. I hooked up the voltmeter to the battery and got roughly the same as my multimeter. Last winter I redid all of the grounds so I know those are good. Now I guess I have to check out the lighter and the wiring. Grr that probably means pulling the blower assembly again....

Check voltage drop across the fuse before pulling anything apart.

You have a voltmeter so use it to measure the voltage drop. Eg one probe on lighter+ and the other on battery+. You can also do this for the grounds. Work your way along the line back to the battery noting where the largest drop is. This is a better test than measuring two voltages with different ground references.

Probably a mixture of poor earth and terminal resistance. The spring terminal in the lighter socket isn’t the best connection method either.

I lose about half a volt on mine.

Yeah those bullet fuses and holders are notorious.

After reading another thread I installed one of these as well. Works great and I don't experience the voltage drop as mentioned by Johnny H.

http://forums.pelicanparts.com/porsche-911-technical-forum/989425-replaced-cigarette-lighter-socket-dual-usb-power-outlet-socket.html

http://forums.pelicanparts.com/uploa...1535903989.jpg

Across the fuse is the easiest place to start.
The power flow from the battery to the top of the switched fuses is from battery to dash 6 pin connector, then to ignition switch, then back to 6 pin connector and then to top fuse bank of switched power.
If the full 12 volts (same as at the battery) reaches the top of the fuses, then the problem is downstream.
Measuring a voltage drop from top to bottom fuse post on the lighter circuit tells you if the fuse or holder is the high resistance problem.
Or measure top fuse post voltage to ground and then bottom fuse post voltage to ground and see if there is a difference.
If you aren’t seeing full battery voltage on the top fuse posts (switched power) the problem is at the 6 pin connector or the ignition switch.

Great instructions from timmy2. I measured around 9 volts at the top fuse post. Looking underneath the dash, I found 3 plugs. Not really knowing which plug was for the ignition switch, I pulled all of them and cleaned them with contact cleaner and Deoxit. Going upside down under the dash I figured out which plug was ignition. After the cleaning I now get the same 10 volts at the lighter. I guess that means the ignition switch. Even at reduced voltage the lighter still powers my GPS and my USB charger. I would rather not mess with the ignition switch.....

You’re not done yet.... :)
Check the voltage to ground on the battery positive terminal post and then again at the back of the two red wires going to the clamp in one connector. (That pair feeds the ignition switch, the single feeds the fuse panel)
I’m thinking you may have a bad or corroded terminal connection at the battery as I wouldn’t expect a 2 volt drop across the ignition switch would hold up for too long. (Heat)

Even better, disconnect battery positive clamp, then with ignition switch turned on to run,measure resistance from battery positive red cables to the switched fuse position. Try different spots on the connector or even get to the wire at the battery connection end and see if the resistance value changes.

check your alternator warning light to make sure its correct too..it can affect exciter circuit

According to first post, its charging correctly. He is getting full 14 volts charging at battery. It is the secondary circuits seeing a voltage that is lower.

Ok, followed the second instructions and measured infinite resistance when the key was off and around .1 ohm with the key on. The battery connections are clean, I redid all the grounds in the spring time. The one between the transmission and the engine was a filthy job. Anyways, I put everything back together and tried the multimeter on the lighter itself. 12 volts! I tried one of my lighter volt meters and 12.1! I think I am going to redo the single hot cable between the battery and the fuse block, it didn't feel good. I wonder if taking the hot cables off and reinstalling cleaned up something?
Thanks timmy2

http://forums.pelicanparts.com/uploa...1536197612.JPG
http://forums.pelicanparts.com/uploa...1536197612.JPG
http://forums.pelicanparts.com/uploa...1536197612.JPG

New battery ground when I put in my Odyssey PC925
http://forums.pelicanparts.com/uploa...1536197612.JPG

You likely knocked off some corrosion moving them. Or they are simply tighter now.
Sounds like you now have a much better reading than before.
Throw a little no-ox or similar treatment on the terminals to keep them free from corrosion.

Everyone talks about cleaning grounds but seldom mention the power and signal wires other than the fuses.