Half a volt....

[oldmako69]

My conundrum...I'm chasing electrical gremlins and have trouble with invisible stuff.

Twin engines.
Twin Batts.
Twin OFF-1-2-BOTH switches, both wired so their output runs to one of the two engines.

This week I pulled the Battery Selector Switches to examine their connections. All were surprisingly good, although the lug on the lead TO one of the engines simply pulled free. So much for quality control at the rigging shop.

Q1. WHY do both engine leads on the back of these switches register .50V when Both battery grounds are disconnected? Switches off and grounds off. Yet, I get .5 on them. The boat is high and dry on the trailer so there is no current reaching the boat through, or because of the salt water.

Q2. Why does one engines trim and tilt zinc show significant wear while the other one looks great?

I know for a fact that I have bilge pump issues, namely neither one works when activated by the float switch. So, I have an Andy Jackson which says there may be something wonky going on in the bilge, but I can't see how this is related to the half-a-volt reading. Just fodder for discussion.

[99yam40]

Just exactly where are you placing the meter leads

[panasonic]

The meter on the disconnected engine lead and where else?

[oldmako69]

The DVM's black lead on the negative battery post closest to the selector switch and the red lead on the cable which connects to the center post on the back of the selector switch which supplies the current to the engine (where the left post is Battery 1 and the right post is Battery 2).

[99yam40]

so you disconnected the negative battery cables from the batteries and then measured the voltage from a positive of switch to a negative battery post.
Correct?

you would read any connection calling for 12 V (like a radio or clock) or bleed over voltage on any positive wire/connection.

What were you looking for when you did this?

[oldmako69]

[QUOTE=99yam40;140065]so you disconnected the negative battery cables from the batteries and then measured the voltage from a positive of switch to a negative battery post.
Correct?

Close. I disconnected the engine lead from the battery selector switch and read the voltage from the lead itself, not the post on the back of the switch.

you would read any connection calling for 12 V (like a radio or clock) or bleed over voltage on any positive wire/connection.

What were you looking for when you did this?

<<I was trying to determine if I had a significant voltage drop in either battery selector switch. I measured the V at the batt, and then at that batts post on the first switch, then again on the second. Then again on the center post which supplies the engine. I thought that perhaps a switch was bad. But, they both test OK WRT to voltage.

I am pretty sure that I have a parasitic voltage loss somewhere, I suspect the bilge float switches as one battery was dead two weeks ago. But here is the kicker, I was unable to start the opposite engine using the good battery, and the running engine would not adequately charge the dead battery.

According to the V-meter on the YAM gauge, it was still only showing 12.3 V after a good 45 mins of idle on the good engine. It seems to me that there is a restriction to current flow somewhere and I am trying to pinpoint it. I figured that I'd start at the batteries and measure voltage as I get closer to the engines and accessories.

Does anyone use and or recommend one of these tools, or similar for finding wiring problems.


https://www.amazon.com/gp/product/B0...=AGCYLCUQLKXQE COLOR]

[fairdeal]

Q2. Why does one engines trim and tilt zinc show significant wear while the other one looks great?

two possibilities come to mind

1. one anode is actually zinc, the other is aluminum
(my understanding is the Yamaha part is aluminum, but aftermarket is available aluminum or zinc - or Mg for that matter)

2. you do not have a good no-resistance shared connection between the battery grounds on the engine. So one is at a slightly different "potential" vs the other

[99yam40]

Does anyone use and or recommend one of these tools, or similar for finding wiring problems.


https://www.amazon.com/gp/product/B0...=AGCYLCUQLKXQE COLOR]

I have used things simular, but not on cars or boats.

it puts out a high frequency signal(I guess) to help trace wires that are open ended or grounded