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Old 01-20-2005, 02:17 PM
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Grounding Cans?

I'm a noob so please be gentle

I have a 58 Chevy Apache. I'm having problems with my brake lights and rear park lights.

The parking lights coming on is hit and miss. The passenger rear would light up most of the time, and the driver rear would light up less than the other. Both lighting up is really rare.

So I decided to take the cans out and look at what was goin on in there. Everything was hooked up (I didn't have a voltage tester to check that out tho), except for the ground.

Now the question I have is... the driver's side can has a ground coming out of it, but the passenger's side doesn't. Is that the way it's supposed to be? Also, where do I hook the ground wire up to? I didn't see anywhere to put the ground wire into or onto.

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Old 01-20-2005, 02:52 PM
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Not familiar with the Apache buckets but older cars like that usually had stamped steel or pot metal tail lights as opposed to the plastic thingies they use now. They normally depended on those metal bodies to ground to the metal of the fenders which in turn grounds to the frame. Break this secondary ground circuit anywhere along the line and no lights!

If you have the light units out of the truck, can you use your battery charger to put +12V to the light lead wire and -12V to the light socket and see if the light works? If it does, move the -12V lead to the body of the light housing and see if it lights. Keep following this trail back to the frame which should be a universal ground 'til you find the weak link. There should be a heavy copper strap from the "-" side of the battery to the frame so it is a good ground.

In the final analysis, you need a solid ground to the little metal socket that the light bulbs screw into. If the grounding trail isn't working due to corrosion, loose rivets, etc., run a ground wire from the frame to the socket. Solder the wire to the socket and screw it to a bare metal spot on the frame with a star washer.
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Old 01-20-2005, 03:28 PM
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Thanks for the reply sir

Well that makes 'some' sense. I don't have a battery charger so, unfortunately, I can't do that suggestion.

I do have a voltimeter now tho... can I use that for anything smart?

Whats that 3rd wire coming out of the apparatus that the lightbulb fits into, anyone? The brake wires go in one hole and the parking wires go in another, one of the holes has a collar that sticks out a little farther than the other (so you can tell which is which I guess, but I don't know) Can't remember which one of the slots (brake or parking) the 3rd wires comes out, since I put it all back together.

Think I should just replace my Turn Signal Relay or go fishing with the voltimeter?

As for that strap from the battery... hrmm. I don't think I have one of those. I have something coming off the negative post, I'll go look and see where it goes. I'm pretty sure it's not the strap you speak of tho. I've seen those in a catalog and know exactly what you're talking about. Does that certain strap make a difference opposed to just a regular ground type wire?
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Old 01-20-2005, 03:48 PM
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I assume your 'voltmeter' is actually a multi meter with volt, amp, and resistance circuits. You can use that to do the same tests I suggested for the current tests. Set the meter to the lowest resistance (ohm) setting and read the resistance between the lightbulb lead and the various ground points I mentioned. You should get a reading of the resistance of the light bulb with no wavering. If the meter bounces to an extremely high number then down to to the baseline number or stays at the very high number, that is the source of your open circuit and no light.

Most old cars use a bare flat braided cable to ground to the frame but it can be any heavy wire. You should be able to follow a wire path from the "-" post on the battery to the engine near the starter (very heavy wire here), to the frame, to the body, to the fenders, etc. There must be a positive, solid connection path from anything that uses electrical power to the ground post on the battery. If you can't find that link, add it. Don't depend on body bolts and fender bolts to complete the circuit. The best way to do this is go to the remote device and imagine yourself as an electron trying to get back to the negative battery post. If you can't find a positive, solid, metal-to-metal path, that is a potential problem. Add a ground wire across any poor grounding path you find. Almost all the electrical problems you run into, and the most experienced rodder has the problem at times, are due to bad grounds.

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Old 01-20-2005, 08:13 PM
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Multimeter, haha. Told ya I was noob

Thanks again, I'm sure learning alot from this community and I really really appreciate it!

The wire from the negative terminal goes to a bolt on the engine, so that should be okay.

Sorry to ask for reiteration, but I'm not quite sure on the flow of current here. Starting from the turn signal relay, it passes through a wire, into the light, then I get slighty unsure... does it then go into the can, then through the screws that hold the can in place, then into the fender, then makes it way back to the "-" post?

Could rust on the screws that hold the can in place cause an open circuit? My truck was painted as well, so there may be paint in there. I'm guessing paint is a poor conducter as well, correct?

By the way, do the problems this truck is having (ie one rear parking light coming on sometimes, then the other, now niether, and no brake lights) sound specifically like a ground problem? And also, do the brake lights require a better circuit than the parking lights?
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Old 01-20-2005, 10:25 PM
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That sounds exactly like an intermittent grounding problem probably caused by a rusty screw or some such 'almost' circuit. Current come from the "+" side of the circuit through the lead wires which is pretty easy for everyone to understand. The current enters the bulb through the lead button on the bottom of the lamp that is in contact with the positive lead wire attached to the bottom of the socket or your 'can'. From there the current passes through the filament, heating it white hot ad generating light.

Of course, this doesn't happen unless the circuit is closed and the current can make its way back to the "-" side of the battery and this is where we all start to get into trouble.

Everyone understands a wiring harness and that you have to have a lead wire to a device for it to work. However, we get really fuzzy on how the ground system is supposed to work. It would be very easy to understand if we installed a parallel 'negative' wiring harness that mirrored the positive one we all install now. If we ran a lead wire from the negative battery terminal to the ground side of each device, it would all make sense.

That is in fact what we do except instead of an individual ground wire we make every metal part of the car part of the ground system by attaching a ground lead wire from that metal part to another metal part that is for sure grounded to the negative battery post. This concept it referred to as a 'buss' in the electrical world. Once a metal part is grounded, you can attach the ground lead from an electrical device to it anywhere and it will deliver the current home.

Two obvious buses on a car are the engine/transmission and the frame. Unfortunately, those two systems are isolated from each other electrically by rubber motor mounts so you need to overtly attach ground wires to make sure they are connected. Less obvious but just as important is the body of the car. It too is mounted using rubber pads and isn't necessarily solidly grounded to the chassis or the engine. You must run a grounding wire to it also.

Finally, bolted-on fenders on older cars are not necessarily in electrical contact with any of the other components so again, a jumper wire is in order. This is what I meant when I gave the analogy of thinking yourself an electron and imagining yourself finding a solid metal-to-metal way home to the battery ground. The guys with fiberglass bodied cars can understand this concept better than the steel body guys because the must run a ground lead and a hot lead to every device. They can't depend on the body being a grounding buss so they avoid that confusing concept.

Back to your bulb, the current flows out of the filament through an internal lead that is attached to the brass base of the bulb. That brass base is in contact with your 'can' which must be in contact with the metal light housing which must be in contact with the fender and so on, clear back to the "-" post on the battery. Your intermittent lights are suffering from a broken circuit in the 'buss' system on your car. You need to track down the reason for that break.
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Old 01-21-2005, 07:12 PM
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Had a similar problem with a utility trailer a couple years ago, after scratching our heads for a few hours and rewiring the entire trailer the problem turned out to be a bad ground from the frame to the box lesson learned, check your grounds twice for good measure.

And yeah, everything willys said
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