I am having an issue with the circuit on my macerator.

Things I know that are good:
Switch is good. (Checked with DVM and the water pump still works.)
Macerator motor is good. (Checked by hooking up to jump box.)
Spare/2nd macerator motor is good. (Checked by hooking up to jump box.)
Ground is good. (Ohmed out to ground behind dash just fine.)
+/Hot side of circuit is good. (Checked with DVM to circuit's ground as well as a different ground.)

When I remove the macerator from the circuit, and only use the DVM to check voltage across the circuit; the DVM reads 12.25VDC when the switch is pushed. (Exactly as it should.)

When I use the + side of the macerator circuit and go to a new/separate ground with the DVM only, the DVM reads 12.25VDC when the switch is pushed. (Exaclty as it should.)

When I hook the macerator into the circuit normally, AND also try to read VDC across the same circuit, the DVM reads .003VDC.
The macerator does not flinch. (Have checked with two macerators.)

When I hook the macerator normally, AND also try to read the
VDC from the + of the circuit, across to a ground lug behind the dash, the DVM reads .003VDC. The macerator does not flinch. (Have checked with two macerators.)

I don't get it. This pretty much defies all EP logic.

I know the switch is good. I know there is no inline cicruit breaker or fuse, and besides, the circuit reads 12.25VDC when no macerator is plugged in. BOTH macerators work fine when hot wired to a 12VDC jump box.

Help!?!?
What am I missing? I will try a new ground tomorrow, as I got too frustrated tonight. Anything else?

Thanks in advance. NO peanut gallery comments please. I am trying to get this fixed tomorrow to head to a Poker Run, and the boat will be at the lake through Memorial Day.

When dealing with a larger load like the macerator (or a starter) you need to do voltage drops along each leg of the circuit. It is likely that you have a corroded connector that is allowing the small current from the DVOM to pass but when you ask it for 30 amps or so there is too much resistance to allow current flow. Set your DVOM on volts, put the leads on either end of each leg and then activate the unit-when the volt reading goes high, you found your bad leg. Then check on either side of all connections and you'll find the bad one.

Dam your no fun.Sorry can't help.Hope you get it fixed by the weekend,I'll probably need to use it but don't worry on after coffee in the am.

That is what I was thinking also you have a broken wire or corroded some where. I see it alot around water and chemical's, voltage there and when the amp draw is high it drops out. If it is possible do you have any jumpers to bypass the boat wiring. Good luck, electical problems are a biotch!!

Thanks everyone. I am going to do some more digging. Its not too hard to replace the wiring from the switch to the macerator and then to ground to test. I think I will try this first.

And I will test it for you every morning this weekend after coffee. you know what are friends for.

3 hours later. I found the problem. The power feeder wire had issues.

Some of the wiring was not factory. I don't know who could have done it, but I know I did not, and Todd did not. There was a butt connector that in the feeder wire from the dash to the switch. The connector was not able to be seen. I only found it by feeling my way down the entire wire with my arm buried up to my elbow. This connector sat in a tray that probably got wet once or twice. The butt connector was full of corrosion. There is/was about 18" of extra wire on that circuit too. Again, VERY strange.

Now I have to go put it all back together.

Thanks everyone.

Brian,
Glad you found it. I cant remember the details but I think I replace the macerator pump once. Good luck with the Poker Run. Go Monsoon.