Running Lights Wiring Question

[tsubaki]

That low voltage will be a result of a backfeed, undersized wire or overloaded wire, corrosion in that length of wire to the front could cause such a problem (voltage drop).
Two wires from the switch won't let you use the system as an anchor light unless you have a ground at the sternlight location (which is possible).
The normal situation is to have each light wire pass by the switch, the grounds from each light (black wire) go to the fuse panel ground.
The switch will be a 3 position switch, off, on (stern lights), on (bow & stern lights).
Three wires will go to the switch, Common (fused hot), sternlight, bowlight.

However if you have a single pole switch then the bow and stern lights will come on together only and this would account for the way you're describing the wires. "2-bow, 2-stern, 2-switch".
If that is the case, at the sternlight tie all the blacks (3) together, then tie all the reds (3) together, take a reading to see if you got 12 volts at that location.
Look at the switch and see where the wire comming from the stern light is going to and make sure the ground is connected to the fuse bus ground.

[greateastern]

I have grey and black wires, the greys go to the switch the blacks I will trace out after work. When I put the meter to the 12v dc wires the meter reads -12.5v dc with the red meter lead on grey and the black meter lead on black. then I change it around and I read 12.5v dc no more - so i figured the grey wire is the ground wire, neg, to the meter. Does that make sense?

[tsubaki]

I probably won't be able to tell you how your meter is supposed to work but normally if you reverse the polarity it will show up as a negetive number on the meter.
Example in a 12 volt system: if the black meter wire connected to a positive wire and the red meter wire connected to the negetive wire it will read -12 volts. Reversing the leads, it will read 12 volts, therefore the red lead is connected to the positive wire and the black lead is connected to the negetive wire.

Now,.....depending on what the "mechanic" that last serviced this spiderweb, you could end up with a number of different possibilities.
Initally it sounds like they are switching the ground. One way to find out is to make a jumper from the battery negetive terminal and test between it and the lights. If you get a reading that is what they have done.
Normally "most" people will observe the black as a ground, that ain't to say this is the case. Gotta see.

[tsubaki]

Originally Posted by greateastern

I have grey and black wires, the greys go to the switch the blacks I will trace out after work. When I put the meter to the 12v dc wires the meter reads -12.5v dc with the red meter lead on grey and the black meter lead on black. then I change it around and I read 12.5v dc no more - so i figured the grey wire is the ground wire, neg, to the meter. Does that make sense?

Yes that should be the case, and is this with the light switch on and both bulbs burning?
There are a lot of variables, if someone derived the negetive from a dashlight panel and a wire broke or bulb blew, this could create a whole number of funny readings.
First try to localise the ground from the lights to their source, as to where they are connected.

You wouldn't believe the mess created by the "mechanics" on a brand new boat that my neighbor bought.
Most all of this is simple but when you get to thinking too hard it makes a bigger mess.
Rewiring does give a lot of piece of mind.

[tsubaki]

Are these the old pull type switches, toggle type or the rocker switches with an indicator light?
Only real difference is the switch having a ground to them.

[macojoe]

Easy! Just rip the thing out of there, and run a new one!! Do I have to think of everything??

[tsubaki]

BEST ROUTE and you can do it a little at the time.

[cterrebonne]

if you still arent getting 12v and dont want to rip all of the wires out and start from scratch replace the blade connector on the switch and the connections at the lights. 99% of the time corrosion with cause the voltage drop. also you messed up when cutting the black loop you need that to be connected it gives power to each bank of the 6 way switch. do this. connect the middle wire on one side directly to the wire that is suppose to bring voltage to the light and test in the front. if you have 12v to the front then its a bad switch or bulb. if no 12v then you have a ground issue.