Swapped positive and negative?

[Tmacmi]

I have spreader lights. They are on their own circuit, just a switch and fuse to spot lights.

I just did a bunch work and now they are blowing their fuse. There is a slight delay, maybe a full second and a half before it blows.

I suspect there is a split in the insulation and its arcing.

But I thought I'd ask if swapping the positive and negative wires would cause fuses to blow.

Wire colors are brown and black, so its not perfectly straight forward.

Thank you

[wholybee]

If it is truly it's own circuit, and nowhere is the ground or positive shared with another device, then swapping polarity should not cause the fuse to blow. Does the light come on for the few seconds before it blows? Is it an LED light or incandescent?

Brown is a normal wire color for positive feeds. Often used for pumps.

[Tmacmi]

Originally Posted by wholybee

If it is truly it's own circuit, and nowhere is the ground or positive shared with another device, then swapping polarity should not cause the fuse to blow. Does the light come on for the few seconds before it blows? Is it an LED light or incandescent?

Brown is a normal wire color for positive feeds. Often used for pumps.

I am confident that nothing else is on the circuit. It was retrofit and I can follow the lines up.

I put the black to ground assuming it would be OK,

Yes, the light comes on for a brief bit. Maybe 2 second or so, then fuse blows.

Incandescent bulb

[sailormed]

Originally wired in series and now in parallel?

[chris95040]

Are the bulbs wired in series (unlikely) or parallel (likely)?

12V or 24V?

How many amps are the bulbs supposed to draw?

How many amps is the "fuse" ?

[Svsumurun]

What does the fuse look like? Melted is too much draw , exploded is a short - the way you describe it sounds like too much draw , a short would usually blow immediately .

[wholybee]

Since it works for a few seconds I would attempt to measure the current. Also, measure the resistance of the circuit. Then remove the bulbs, and measure again. If the bulbs are out, and the circuit is not open, then there is a short somewhere.

[Squanderbucks]

Who wired the switch? The hot wire should have the switch in it and come from the fuse or breaker. The ground wire should go to the ground block.
The ground should not be attached to the switch in any way.

[donradcliffe]

Incandescent spreader lights typically draw 5 amps per bulb. If it is a DIY rewire, you may be using a 5 amp breaker. Swapping polarity will not help.

[Brewgyver]

Originally Posted by Squanderbucks

Who wired the switch? The hot wire should have the switch in it and come from the fuse or breaker. The ground wire should go to the ground block.
The ground should not be attached to the switch in any way.

Many switches with pilot lights do require a ground connection.

[thunderhoof]

It sounds like the fuse is rated too close to the current draw. A typical 5 amp fuse will blow in about 1 second with a 10 amp draw. The main purpose of the fuse is to protect the boat if there is a possible short circuit, not to blow if the current is a little above expected.
The best trouble shooting would be to replace the fuse with an ammeter to check the current draw. If the current draw is reasonable, and the lights operate, use a fuse rated about 50% over the measured load.
I would not swap positive and negative wires -black is normally negative. With no power applied use an ohmmeter to see if either lead is tied to the mast. Neither should be but worst case, that one should be the negative side on most boats.

[hlev00]

To your original question, incandescent lights work fine with negative and positive swapped. LED’s just won’t light if reversed.