There are times I see the TL being connected to batt (+) and/or batt (-).
1. to energize GROUNDSIDE switch solenoid using a test light, solenoid plugged in; KOEO - TL to batt (-) touching control wire and when commanded ON/OFF, TL flickers; wiring integrity is assumed ok.
2. to test for OPEN on the same groundside circuit, solenoid is unplugged and TL connected to batt (+)...
I watched 2012 Chevy Cruze where testing was being done on the groundside elec. thermostat and TL was used connected to batt (+) and the circuit PLUGGED IN.
Is there a rule of thumb when to connect to batt (+) or batt (-), circuit plugged in or unplugged or does it depend on the amp rate of the TL and the amp rate of component tested.
When testing a ground-side switched circuit, connecting the test light to ground tells us several things about the circuit. Probing both sides of the solenoid, with the coil commanded off we should see power on both sides. If so, then we can know that the power side is good, the coil is not open and there is no short to ground on neither the control wire nor the driver. So that is a lot of information very quickly. Testing again with the coil commanded on we should see power on only one side, that would say that there is not an open in the control wire and the driver is good. If so, then the solenoid should function normally.
If the test light does light even when the coil is commanded off then it is time to unplug the solenoid and test both sides of the harness side connector noting which terminal has power, that is the supply wire. Move the test light to B+ and test the control wire on the harness side connector, still with the coil commanded off, under normal operation the test light should not light but it may as we just saw that the test light did not illuminate when it should have, indicating that either the control side is grounded unexpectedly or the coil is open. If the test light did not light then the culprit is the coil. If the test light does light the next step would be to unplug the computer and do the same test again. If the test light does not light then the problem is in the computer, likely a shorted driver. If it does light there is a short to ground in the control wire.
So you asked if there was a rule of thumb on when to connect to B+ or ground and the answer is that we use the method that is appropriate for our test. Regarding your "circuit plugged in or unplugged" question, unplugging the component removes the component from the equation and also splits the circuit into power supply side and ground side - divide and conquer. We also can then see if the there is an open in the solenoid if the control side tests fine and there was not power on both sides of the solenoid when the coil was commanded off and the control side has no short to ground then the coil is open or there is a bad connection between either the power or ground side.
In regard to energizing a solenoid with a test light - even an incandescent test light typically draws only 150 milliamps give or take, so the coil may not energize even it is properly powered. I just went and tried this test on a little VSV for Evap solenoid and it would only energize the solenoid for an instant if the bulb were allowed to cool between tests, if the bulb was already hot there wasn't even enough current flow to energize it at all. An LED test light has no hope of ever energizing a solenoid.
Hey guys,
Good question robert.lesaca. And good answer Gary.
I'm moving this thread to the Diagnostic Tools & Techniques section. I think you'll get more help there.
HI ALL IN THE FORUM I HAVE A QUESTION ABOUT TEST LIGHTS
IF I TEST A COMPUTER DRIVER IS ACCURATE THE LED LIGHT I FEEL IS MORE SAFE
BECAUSE OF THE COURRENT DRAW FROM LED
90_Rooster wrote: I was wondering if anyone has a preference when it comes to test lights? Like the bulb vs a fuse type...maybe it depends on what being worked on
Thanks!
I think I tend towards fuse type? Or maybe that's because it's all I've owned. :lol: Nothing against bulb type at all, just the way it worked out.
HI ALL IN THE FORUM I HAVE A QUESTION ABOUT TEST LIGHTS
IF I TEST A COMPUTER DRIVER IS ACCURATE THE LED LIGHT I FEEL IS MORE SAFE
BECAUSE OF THE COURRENT DRAW FROM LED
THANK YOU SO MUCH
The LED is definitely safer overall, no doubt. Personally, I don't have a problem with using an incandescent light on computer drivers, as long as the normal current load for that driver exceeds the light. i.e. A purge valve that can draw 500mA, so I'm safe using the 200mA incandescent test light.
On the other hand, an instrument cluster warning light driver that draws less than 200mA would get an LED test light.
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