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Old 06-25-2009, 08:10 PM   #1
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Re: Electical questions?

Is that an alarm wire, or the switch to make the School lights up top work when the door is opened? I have a dash switch that can power or defeat those lights...

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Old 06-25-2009, 10:17 PM   #2
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Re: Electical questions?

I am 99.9% positive those wires and that switch are for activating the flashing red lights. A driver would arm the 8 ways with a master switch. Then they push a button prior to a stop which activates the flashing amber lights. At the stop they would open the door, activating a third switch which would kill the amber lights and turn on the flashing red lights.

Could you use that wiring? I suppose assuming it is of an appropriate gauge, but I'm fairly certain that wiring just operated relays so it's likely that it's of a smaller gauge making it unsuitable for any sort of current draw. It also would most likely only work with the key on and the master switch armed. Go buy a test light and a cheap meter.
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Old 06-25-2009, 10:19 PM   #3
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Re: Electical questions?

Quote:
Originally Posted by vanguy67
Have you bought a test light yet?? Best 5 bucks you'll spend! Using your new test light you can find out what's hot (key on AND key off) and what's not.
Just a word of warning about those test lights. If you have *any* air circuits (small plastic tubes for air that look like really nice thick wires), do NOT puncture them. I offer this advice because I just barely prevented someone from doing that to my fast idle control o my bus.

If you don't have any air operated options on your bus, then ignore this.

I use my multi-meter instead of a test light, but it isn't as convenient as a test light. I really should spring for the right tool.

hope this helps,
jim
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Old 06-25-2009, 11:08 PM   #4
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Re: Electical questions?

Quote:
Originally Posted by baadpuppy
Quote:
Originally Posted by vanguy67
I use my multi-meter instead of a test light, but it isn't as convenient as a test light. I really should spring for the right tool.
Really a person needs both. There are times when one is appropriate and times when the other is appropriate. I used to use my meter all the time...until I got my ass burnt a few times. Meters are great because you can use them on an active circuit, they do more than just check for voltage, and they're accurate. Unfortunately, they really place no load on a circuit.

How did I get my ass burnt you might ask? I was checking a fuel pump. I had no fuel pressure and the pump wasn't running. I put my meter to the wires and had 12 volts at the pump. I figured I had a slam dunk and proceded to drop the tank and replace the pump. I got the job all done and turned the key only to get the same results. I thought I had a bunk pump off the shelf so I dropped the tank again and jumped 12 volts to it from a jumper pack and it spun right up. The problem? I had a broken wire. The meter registered 12 volts, but the resistance was excessive and as soon as a real load was placed on the circuit I lost all my power. Of course only having 10 volts at a fuel pump can cause low pressure and excessive current draw, but 10 volts is hardly discernible from 12 volts with a test light. Therefore I now use BOTH a test light and meter to check fuel pumps.
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Old 06-29-2009, 10:32 PM   #5
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Re: Electical questions?

Quote:
Just a word of warning about those test lights. If you have *any* air circuits (small plastic tubes for air that look like really nice thick wires), do NOT puncture them. I offer this advice because I just barely prevented someone from doing that to my fast idle control o my bus.
You really shouldn't puncture ANY wire insulation with test leads, especially in a vehicle. All it takes is a pinhole, and condensation will get in and turn your wires to green powder. Sometimes you can't even find the hole, but when you feel along the wire you'll find a place where it is stiff and resists bending, cut it open and there's your powder. Even worse, the powder will show 12 volts through the wire when there is no load.

Do yourself a favor, and get in the habit of measuring at the terminals. Make sure your mechanics do, too.

If the power in the wire seems good, do as The Experience says and measure across the load with the power on. If the voltage is low, measure battery to hot, or hot to the frame, and ground to the frame. If you have voltage between battery hot and load hot, or if load hot to frame is much less than battery hot to frame, then there is resistance in the hot side. If you have voltage between the load ground and the frame, there is a high resistance (bad) ground.

And yes, I agree the handle switch starts and stops the red lights if armed at the beginning of a run. When I was in school, there were no yellow "Jersey" lights to trigger, but there were door handle switches on the reds.
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Old 06-29-2009, 10:52 PM   #6
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Re: Electical questions?

Sometimes you can't help but puncture the wire because a terminal end is impossible to find. In those rare instances I've found this stuff to be invaluable.

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Old 06-29-2009, 11:32 PM   #7
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Re: Electical questions?

Quote:
Sometimes you can't help but puncture the wire because a terminal end is impossible to find.
Agreed, but I've seen too many cases where puncturing the insulation is the first thing, not the last thing done. When I see someone doing it on exposed trailer wiring, and not repairing it, I believe they are setting you up for repeat business. These people lose my trust.

Quote:
In those rare instances I've found this stuff to be invaluable.
I like the stuff for waterproofing antenna connections. Go up 100+ feet, and after you connect your cable to your antenna, wrap a couple of layers of electricians' rubber tape, followed by a couple of layers of 89-cent plastic electric tape, and then goop it with the liquid. It lasts for decades. It works much better than the 'taffy' some antenna people sell. Ive found water inside 'taffy', but never under rubber tape. And it cuts off cleaner, too. Just wear old pants and shoes when daubing it on in the wind. But I digress . . . . .
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