Four electrical questions

Because anything electrical will already be earthed back to the battery via a connection to the chassis or else it wouldn't run in normal operation. If you connect a direct positive feed and the device runs it tells you that both the device and the earth side is ok. If the device still doesn't run it could either be broken or the earth side is not making contact. In that case you need to add a negative feed to check the device fully.

-- Dave Baker

Thanks Dave! Ok, this makes sense, as the blower motor is mounted in a metal duct whihc is connected to the firewall. And it did test ok (it was brand new--it better have :) ).

But when I tired the same test with just one positive wire for my radiator fan, it did not work, not until I also connected the negative wire. Maybe because the fan motor is encased in a plastic support frame?

Julie

You can probably clip the aligator to a nail and stick that in the socket. I use a piece of thick heavy bared copper wire.

As for the radiator fan motor not comming on when you probe it, that might be due to the location of the thermal switch which only completes the circuit when the rad heats up. I don't know enough about them to say for sure.

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------------------------------------------------------------------------------ William R Watt National Capital FreeNet Ottawa's free community network homepage:

Many auto items even lamps have both a positive drive wire and a (Often black) ground wire thei ensures the ground stays good even in old age when the mounting frame connection has rusted.

If you only use it for testing and stop when it burns your fingers it will be fairly safe.

For a permanent rewire you should use wire as thick as was there from the factory.

An inline fuse right close to the battery connection could save you from connecting to a wrong pin and starting a fire in the test lead.

I've only got one question. :)

Why not use a test lamp (low wattage bulb with earth lead attached) rather than jumper leads? In most cases it'll tell you as much, and more, with a lot less risk of setting your car alight. Or worse still, providing a path for the smoke to escape from delicate electronic components -- around which an LED is an even safer option.

Jumper leads can be fine for bench testing but need to be used with extreme caution for in car diagnostics.

-- John H

Thanks William. What I meant was is there a way to get a secure connection, so I can free up my hands and body to do something else if need be? Right now, I use a paper clip, which works, but it won't stay in place if need be.

Oh, the fan comes on ok, when both positive and negative are jumpered. I am just trying to find a way to test my coolant temperature sensor now. My manual has some instructions, so I will have to check there. :)

Julie

Usually a test lamp will only tell you if you have voltage present, not if the motor will run when connected to the electrical source. Test lamps are handy items, but not necessarily for this.

By the way, Julie, you can get in inline fuse holder at Autozone for a couple of bucks. Maybe that is more than you would like to spend.

Thanks. They were $11.49 each at Radio shack, and I had been considering making 6-8 jumper wires, necessitating spending $75-$95, which seemed a bit much. So the AZ one sounds like a better deal. Anyway, I have to save money, in case I end up having to do costly engine repairs due to the low oil pressure problem. :)

Julie

Ok, nice redundancy feature I guess. Surprising for a Chevy Cavalier though.

My fear is I am always tempted to grap the paper clips stuck in the alligator clips, which are long and wobbly, so I can stick them more easily into male terminals. But if the wires are live, I could be in for quite shock.

Thanks John,

Julie

Not likely.

I have some old harnesses around and have taken some of their plugs to make ends for my jumper cables. I have a spade and a pole one so far. The rest have been ok with needles or paper clips.

You might want to go to a wrecker and tell them you want some old plug pigtails. (plug/socket and 3" or so of wire) They should be cheap.

You also can get the plastic holders for inline glass fuses for about a buck or so. The kind they use on radios or CB's.

Mike

Very correct on the shock aspect , John.

One of my instructors, Carl Roemer, taught all his classes to always remove our rings (wedding bands and ornamental jewelry). Get a battery discharge through a wedding ring, and you can well lose that finger.