Multi-meter question

Didn't know exactly where to post this question, but I figured this was as good a place as any.

Last time I hooked up my 4x8 utility trailer, the trailer lights didn't work when I plugged into the vehicle wiring outlet. Yesterday, I was simply checking the vehicle plug to ensure it was getting power to it with my multi-meter. When on DC voltage, the left turn signal on, the display on the multi-meter would blink like the turn signal, but the voltage I was expecting it to show (12V +/-) was not displaying, just "0.L" blinking. Does that mean my multi-meter needs a new battery, or is toast? It's pretty old. OTOH, I checked it in the house on AC voltage, and that display shows 120 V +/-, so that seems ok...

 

Depending on what brand the multimeter is, the meter may take a second or two to "autorange" the voltage. Before it can display the voltage, it is gone because of the cycling of the flasher. My Fluke 87V is like that.

 

My Fluke offers a setting for the min and max. The blinker fluctuations (as mentioned) are happening pretty quickly. If it was me I would set your range correctly and then set a min/max and let it record what happens. If you want you can get a cheap one with a needle that moves. The OL means overload and that can happen if the range isn’t set properly or the auto adjustment is happening.

For reference (not that I approve of this one)…
Gardner Bender GMT-312 Analog Multimeter, 5 Function / 12 Range, 300V AC/DC, for AC / DC Voltage & Current, Resistance, Continuity & Batteries , Black https://www.amazon.com/dp/B00002N5EX

 

I did it again today, and what is flashing on the turn signals is 0.L. When I check the pin for when the lights are on, it shows 12V solid. That makes sense that the voltage display will not show 12V since it cuts out so quickly. I guess the fact that something is showing and flashing means the outlet is working.

The multi-meter is a Fluke that my son got when he attended UTI in Phoenix quite some time back.

I guess it's on to checking the trailer wiring.

 

I think you either have a problem with the circuit or your measuring it wrong. OL on a multimeter sometimes is short for overload. Put the range at higher setting and see if you still get OL.

Even a cheap un-fused bomb multimeter can measure this stuff

 

Probably measuring it wrong. I am totally unfamiliar with using a multi-meter. I'm going to do some research.

 

I have a multimeter that I really like... but when working on 12v automobiles, a simple test light is usually my go-to.



And to round out the toolbox, a continuity tester will help you find ground pretty easy, along with troubleshooting wire runs, etc.




If you want to get really fancy, you get a tester that will indicate negative or positive... but requires hooking it up to both a negative and positive source. (This is much easier on smaller vehicles, like motorcycles):

 

OL is not overload its open loop. Hes not going to overload his mm on a 12V circuit. The slow meters switch to OL then spit out the reading but since the voltage is constantly changing the meter is too slow to spit anything out.

A test light would be better in this case or a better MM.

 

Exactly what's happening. The display takes a millisecond to go from the 0.L initially showing to the voltage reading, but then the voltage disappears when the turn signal blinks. I'm going to get a test light which seems more useful in this situation.

Does anyone have a tried and true method to check out the trailer wiring?

 

For the turn signals and flashing stuff I'd go with 2 people and a test lamp.

 

Shift the decimal point so it reads 00.0 in the VDC mode. The range on the Fluke being manually set will allow it to react and show the proper voltage without "auto ranging".
Also ensure you have a "good" ground, not a painted surface. Run a wire to the negative terminal, then back to the connector for your MM connection for 0 volt, black lead.