problem with connecting a battery switch

[TitanTn]

Okay, I need some help. Please hang through this description as it may get a little lengthy:

I've had a one battery setup until this winter. That battery is weak, but I hope to make it through this season and replace it over next winter. So this winter I installed a Perko switch front - http://assets.academy.com/mgen/06/10183206.jpg?is=500,500 and back - http://www.bassclubdigest.org/summer08/features/4-position-perko-switch.jpg

So I installed battery 1 (weak battery) to Perko Batt 1, and the new battery to Perko Batt 2. The common post receives the cable from the engine which powers the whole boat. Pretty simple and straight-forward.

Battery 1 (weak) has been on a tender all winter. When I started it this spring, it would barely turn the engine over, but it did start. I tested that Battery 2 powered the boat but I didn't attempt to use it to start until this weekend. It wouldn't even turn the engine over. Nothing. Silence.

So I charged it overnight and tried again tonight. It did turn the engine over, but it acts like the weak battery. It barely turns it over. Hmmm.

Is it possible for these switches to be bad? This is an older, used switch that I've had for quite some time. Any other thoughts? I will have to go through the system and check grounds, etc, but I thought I'd check opinions before I jumped in with both feet.

[CornRickey]

Take the cables off the back and bolt them together to eliminate the switch and see what happens. Take to batts to a shop and have them load tested. There probably bad. They need to be the same rating and in the same condition if you plan to run it on both.

[Wylietunes]

First test the static voltage of both batteries, then test the alternator output. If those readings are good, then do a voltage-drop test across the posts of the switch. If the switch is bad or faulty in any way, you will have significant voltage across those terminals. with the switch on BATT-1, connect your meters GND lead to the C post of the switch and the POS lead to the 1 terminal. Repeat test with switch on 2 and meters POS lead on post 2. I do not know what the manufacturer would consider excessive, but IMO, anything over .5v is too much. A good switch should not have any voltage loss across it. Next step would be to pull the batteries and have them tested with an inductance tester.

[TitanTn]

Did a bunch of testing today and found that the voltage at the batteries is okay during cranking (11 + volts), but at the starter it drops to 8-9. The cabling from the batteries to the starter is not overkill, but it's worked until this year. But I tested with some shorter 2 gauge cabling I have on hand and it turned over great. So, I'm ordering some more 2 gauge cabling today.

[michael hunter]

Probably not so much the size of the cables the old ones are most likely corroded inside.

[up4boating]

My bet would be on a starter on it's way out

[Wylietunes]

A voltage drop test on that main starter cable will allow you to see inside, so to speak. A cable that corroding under the insulation may not be visible from the outside, but the added resistance will show up in a voltage drop test.

[TitanTn]

I replaced the primary cables with new 2 AWG cables and everything now works as it should. I don't know what the issue was because the cables I pulled out were only two years old. They were 4 AWG, so maybe that was a factor, but they had been working before.