Positive ground

[hicrop10]

As many of you may be aware that I’m restoring my 1964 B87 tractor.This positive ground is giving me a run for the money.When I use my test light to check things I’m finding everything to be hot,even the steering column is hot.My truck has a Cummins motor it’s a dt335,which has a fuel shut off solinord, that doesn’t seems to be working right,the motor runs fine if I use the manual shutoff. Any help would be greatly appreciated.

[Geoff Weeks]

At that vintage polarity only matters with some gauges, alternator (but not generator) and any radio with transistors.

What type of test light are you using? If you are using a non powered one like pictured, normally the end with the alligator clip gets hooked to ground (positive in your case) and the item being tested wire will supply the negative.

Cummins solenoid doesn't care about polarity, it will work just fine on positive ground.

[hicrop10]

6 minutes ago, Geoff Weeks said:

At that vintage polarity only matters with some gauges, alternator (but not generator) and any radio with transistors.

What type of test light are you using? If you are using a non powered one like pictured, normally the end with the alligator clip gets hooked to ground (positive in your case) and the item being tested wire will supply the negative.

Cummins solenoid doesn't care about polarity, it will work just fine on positive ground.

I am using the type pictured,and I had the clip on the negative post I have 2 12 volt batteries 

[Geoff Weeks]

Ok, then anything that is ground, the frame, the steering column, etc will light the light. Anything that has "hot" power will not. 

Move the clip to the positive (ground side) and the light will light when the probe touches something that is "live".

I think what is confusing you is you are so used to positive being "hot" and negative being "ground", but your system is the reverse.

Edited 4 hours ago by Geoff Weeks

[hicrop10]

What’s the difference between hot and live,aren’t they the same?

[Geoff Weeks]

yes, just different terms. It refers to the the wire that is carrying the current when one side of the circuit is grounded to the frame or surrounding metal. 

 Look at it this way:

 You could run two wires from the battery (positive and negative) to every device and the surrounding metal could be "neutral" neither + or -. Instead of doing that you tie one side (either positive or negative) to the metal and eliminate one of the two wires.

 Ships  houses, many things use the two wire method so any metal you touch is not a part of the circuit. 

Low voltage vehicles they cut the wiring in 1/2 by using the body for one of the wires. 

It makes no difference from an operational stand point which polarity  is tied to the chassie. Positive or negative, it makes no difference,  Light bulbs, most motor, many gauges, will function without any changes. Volt meters and some designs of temp and fuel gauges, you have to have the + lead connect to "ground" and - lead goes to feed (hot, live, whatever term you use).   

Edited 2 hours ago by Geoff Weeks

[hicrop10]

Tks

[Geoff Weeks]

Another way to look at it that may help:

If you had a "normal" truck and wanted to see why the Cummins fuel solenoid wasn't working and what to check to see if there was power there with the key on, you would clip one end of the test light to either the frame or engine block and use the pointy end to the stud with the wire from the ignition switch, and if the light lit, you would know you had power to the solenoid. Nothing is different when the truck is positive ground, you hook the test light up exactly the same and the results you see are exactly those of a "normal" truck.

[hicrop10]

Will check it out tomorrow morning Tks again