The Stovebolt Site Forums The Shop Area The Electrical Bay negative current?

OK, so I'm working on my headlights again, long story short I have no dims, no front marker lights, and only one headlight works on brights. Replaced dimmer switch and headlight switch today, no go on either.

I decided to check the headlight sockets with my meter, on the passenger side I have 12v on brights, nothing at all on dims. Pass. marker light no current at all. Both blinkers work, but the pass. one is dim, only powers up to 6v on blink.

Here's the kicker, and danged if I can understand it: Driver's side headlight socket reads -11v on brights, nothing on dims. No typo, that's NEGATIVE 11 volts. I don't understand, I don't think I've ever seen negative volts on a car. Does this mean there's a short? Although I can't understand how there could be one, power for the pass. light comes from the driver's side from what I can tell, no?

I thought maybe it was my relay, haven't checked it yet but it's on the inside of the radiator support, and that wouldn't explain why the marker lights have no power, as they don't go thru the relay.

I really need some help understanding this, I have to drive the truck 700-plus miles on Wednesday, and I'd love to have headlights before I go.
Thanks,

Tony

Well, I hate to be the one to tell you but current is electron flow. Electrons carry a negative charge. In other words, if your system has the negative side of the battery to ground or frame, then the current flow is out the negative side of your battery through the various systems and ends up at the positive side of the battery. This ain't no big deal. What I think the guys will want to know is...where did this all start? Did you change some wire or component, or did it just happen. These guys here are really shape, so give them as much infor as you can and they will give you back the things to check and possible causes and effects. Good luck

original wiring, 44 years old? the only place to start with that mess of malfunctions is a whole new harness, including all plug connectors .... want the meter to read + instead of - switch the meter leads

Bill

I understand that current is electrons, but that theory or answer doesn't seem to be correct, as it would seem that if it were true, then all of the readings would have the negative sign in front of them, and in my 16-ish years of working on vehicles, I've never seen it.
As far as what happened, I couldn't tell you, they worked fine, then I changed the gas tank (only touched one wire, the one for the sending unit) and the next time I turned on the lights, this problem popped up. I've checked all the wires that I can see for cracks/shorts/missing insulation, and they all appear to be in good shape. No blown fuses, nothing.

I don't mean to sound disrespectful, I appreciate the reply, but it just doesn't make sense to me. I checked grounds, they seem to be fine, so what I plan for tomorrow is to run a ground wire from the battery and use my meter on all the wires in the circuit, starting at the fuse block, and out until I have a loss of current, or negative reading again.

Any other ideas are always appreciated
Thanks again,

Tony

Like I said, it ain't no big deal. You must remember, you are reading volts, not amps or current. If you have your meter's black lead to the negative side of the battery or frame then the readings will be positive (or should be) on the meter. I would start with the feed side of the headlight switch. Is it 12 volts? Output side of the switch, both headlights and markers...12 volts? Dimmer switch input...12 volts? Output of dimmer switch both hi and low...12 volts? Move on the the light sockets. What do they read? If as you stated, you are ging to use a lead for your meter to ground and you see 12 volts all the way along then I think you have a bad ground in your headlight housings somewhere. It's a pain but I run all grounds from the lights to the frame. BTW, you do have a strap between the cab and frame and frame to battery, right? Good luck.

As stated the bad ground issue can make you crazy. Understand that all the tin on you truck is part of the circuit, so between a headlight bucket and the frame there are lots of places to get an open circuit. Extra ground straps from body to frame is also something to check.
Hang in there a keep checking you'll find the problem.

I'm not sure about a strap from the body to the frame, I'll have to look at that. I know at the battery, it's main cable to the header bolt on the head, and also a small wire to the radiator support. Not sure as how the body is grounded to the frame, but it makes sense for it to need that.

I don't believe I've ever seen a battery grounded to the frame as well as the body and engine, but is it something I should look into for better grounds? I'm not saying they don't do it, but I just don't remember ever seeing it.
Bad news for troubleshooting today, though... The wife wants to go for a ride instead of working on the Chevy, so I'm stuck thinking about it for another few hours until we get back from wherever we go...

Thanks again, and looking forward to a simple solution,
Tony

The only way you could get a negative voltage is if the point that you are using to measure the voltage is more negative than what you have your negative meter lead hooked to. Since the only source of a negative voltage is the battery you can't have less negative voltage than that. I have seen weird reading when the meter battery is low. Try another meter or buy a test light they are cheap and all you really want to know is will it light the bulb. Even if you had a -11 volts on the bulb it wouldn't care if current is moving through the filament it will generate heat and light no matter which direction it is going.

Thanks for clearing that up, Neil. I don't know if the meter's bad, I just picked it up the other day, $20 cheapy from Orielly. Not sure if I'm going to get on it tonight, we're supposed to be under a severe weather warning until 11 tonight, maybe tornadoes so I don't want to start, get looking, and lose power in the garage. Plus I like watching storms I'll be getting on it in the morning.

OK, so I have headlights now, but my parking lights only work when the switch is half-pulled. Is this normal? I don't believe so, I think they worked before. Any suggestions? I can't find any wires that don't appear to be working, test light says they have current except when the switch is all the way out. I'm doing a bulb run, just throwing this question out there before I go, I'll give a complete update what I found when I get done.

Thanks,
Tony

I would think that the parking lights should be on if the headlights are on. It may be a switch problem. Glad to know the headlight are working. At least you are making progress.

I believe headlights on, park lights off is normal on a '64. I know its normal on a '54.

I'm not sure when that was changed, but I suspect it was a 70's or 80's thing.

Parklights are not on when headlights are on. There is a way to get them to come on, but it is not factory and you don't need it to drive your 700 miles. Check back after you're done!

That makes me feel better. I thought I remembered them on, but I guess maybe I was wrong. Thanks for putting a smile on my face, all

I'll update tomorrow, wife says it's time for bed.

Thanks again,
Tony