Compartment Lights Voltage Drop

[JayCee102]

When I test the voltage at the switch, I have 12+ volts. When I switch it to compartment, those pins have 12+ volts. When I connect the wire that leads to the compartment lights, voltage drops to 0. I disconnected all the bulbs. Voltage did not drop. I tested the leads to each light individually and had 12+ volts. The instant I put any bulb in any spot, voltage goes to 0 and none of the other leads has voltage. Bulbs don't light.

I think I'm going to upgrade them to a newer led style fixture but I'm worried nothing will change. The bulbs are the old style fuse lamps.

Thanks.

[CatFan]

Where exactly are you putting your negative meter lead? You can get fooled on incandescent lighting circuits.

[JayCee102]

I put it to the negative that goes to the light fixture. I also tried putting it to a negative under my dash that's on a gauge. It didn't seem to matter where I grounded it.

[JayCee102]

But also none of the bulbs light up at all. So I assume there's a wiring issue I need to deal with. All the lights share a common ground they tie in to. I need to see where this ground leads to and check it's connection I think.

[kls2020]

Sounds like You have a problem with extra resistance in the circuit causing the voltage drop when you attempt to energize the lights . Could be the light switch itself or a splice /connection in the wiring . With no load you read full voltage but when you introduce load most of the voltage is dropped across the problem component .<br>
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Start by testing the light switch . put your meter leads across the switch and operate the switch . If you read 12 volts the switch is bad&nbsp; ( normally volts will drop to zero +/- with a good switch). You can also check the wires from end to end by de-energizing the wire and with your meter set to OHMS work your way from the source end all the way though the circuit leaving one meter lead connected on the source end .

[JayCee102]

Explain "put your meter leads across the switch" please. Where on the switch and which leads?

[billnorman1]

Explain "put your meter leads across the switch" please. Where on the switch and which leads?

A suggestion. Get a long wire, connect it to the negative side of your main battery, connect the meter negative lead to that wire. Put your meter on DCV, check the input wire to the switch with the switch off it should read about 12 volts. Turn the switch "on" you should have about 12 volts on the wire to the compartment lights. If you put bulb in and the volts goes way down to zero on that wire, the switch is bad if you still have 12 volts on the first wire you checked. If you have 12 volts to the bulb with a bulb installed and it still doesn't light, you have a negative (ground) issue.

[JayCee102]

When I switch the switch, the middle pins still have 12v because that's where the power comes in. The pins at the top become hot at 12v with no bulb in. When I put in a bulb, volts go to 0 at those pins. I reversed them too. So I put the wires at the other end of the switch and the same thing happened. With courtesy lights, I switch it and have 12 volts on those pins with or without the bulb in.

[CatFan]

When I switch the switch, the middle pins still have 12v because that's where the power comes in. The pins at the top become hot at 12v with no bulb in. When I put in a bulb, volts go to 0 at those pins. I reversed them too. So I put the wires at the other end of the switch and the same thing happened. With courtesy lights, I switch it and have 12 volts on those pins with or without the bulb in.

Sounds like the switch is bad. Try jumping across the switch and see what happens.

[bobcoy]

Sounds like there is no load until the bulb is put in. Bad connection in the switch or somewhere else. With no load any kind of connection will show the battery voltage until it has a load on it. Bob

[JayCee102]

Jumping across the switch causes the other side to go to 0 when the bulb goes in.

[CatFan]

Jumping across the switch causes the other side to go to 0 when the bulb goes in.

If you are jumped across the switch, the input and output of the switch are at the same voltage.

[JayCee102]

When not jumpered, the switch says 12v even with the bulb in, but that's courtesy lights. The compartment lights are the ones causing the switch to go to 0.

[JayCee102]

Regardless of the side of the switch they are connected to, touching the wire for the lights to the switch causes the voltage at the pin to read 0.

[billnorman1]

Carefully read my earlier post. If you have 12 volts when you start and when the bulb is inserted the volts go to zero, there is a bad connection somewhere obviously. If you still have 12 volts on the switch input wire, which goes through a fuse or a current limiter before the switch, after inserting the bulb, and the wire going to the light, go to the bulb socket and if you have 12 volts on BOTH sides of the bulb, the ground is the issue.

[wmitch2]

Remove the bulb, put your meter on OHM's and test the switch. Read across the switch with the switch OFF. Meter should not move or will flash "1". Turn switch to ON and meter should read "0". If no reading, then the switch is bad.

[JayCee102]

When you say read across the switch, what do you mean? Which pins do I put the leads on? It's DPDT so there's 6.

[lpugh]

Remove the bulb, put your meter on OHM's and test the switch. Read across the switch with the switch OFF. Meter should not move or will flash "1". Turn switch to ON and meter should read "0". If no reading, then the switch is bad.

ohm meter is piss poor for checking poor connections. Voltage drop only. An ohm meter can read very near 0 and still not pass any current
Example: if a battery cable has only one good strand of wire making a connection it may very well have 0 ohms resistance, think it will crank the motor
another example is small bulbs with less than 2 ohms, 2 divided by 12 = 6 amps, wow you dont have enough alternator and battery to run all the lights on your car,
resistance creates heat (IE loads) which changes resistance even further. Voltage drop test overcome this issue. You can if you choose to use the voltage drop to calculate the loaded circuit resistance

[wmitch2]

ohm meter is piss poor for checking poor connections. Voltage drop only. An ohm meter can read very near 0 and still not pass any current
Example: if a battery cable has only one good strand of wire making a connection it may very well have 0 ohms resistance, think it will crank the motor
another example is small bulbs with less than 2 ohms, 2 divided by 12 = 6 amps, wow you dont have enough alternator and battery to run all the lights on your car,
resistance creates heat (IE loads) which changes resistance even further. Voltage drop test overcome this issue. You can if you choose to use the voltage drop to calculate the loaded circuit resistance

I agree, but you're making it too technical for doing a simple job. I'm just checking to see if the SWITCH is bad, not if the connection is weak.

JayCee102 Here's a diagram on which pins to test across.

[JayCee102]

I'm sorry for my ignorance. I know what the pins go to and I know how a DPDT works but I just don't know what you mean when you say test "across". That was the only part I was confused on. What pins do I put the leads on?