Peer,

This is not any kind of a criticism of of your language capability. (Your English is much better than my German.)
The blue finned thing is the isolator and the round thing below it is the boost solenoid. Agree?
(Remember I have another '73 23' and know the issues well.)

Are you saying the the house lights stay on when you remove the cables to the outboard side of the boost solenoid, but go out when you remove the wire from the house terminal of the isolator?

Ken wrote: I question your diagnosis in that to have a failure that you are describing, it would take a double shorted diode in the isolator and no power being supplied by the house battery.

I have been straining to get this figured out and Ken may be mistaken.... (I never thought I would write that. - Either Ken)
If the alternator to engine battery went solid (as opposed to open) then this could happen, but it would require some creative rewiring as the terminal that is the central to all the 12V house is that post in the boost contactor. This would also make the alternator terminal hot when it should not be, but that should cause no other issues.

If the both diodes solid is correct, that is a very strange case. In all my years of 12V electrics, I have only seen one isolator diode go solid. These typically fail open when they do fail and that is just not common. And the rarely both fail. (Lightning strikes are another matter.)

I have to believe that that there is something there that should not be.

A simple test with a meter will confirm that the isolator has failed. An ohmmeter reading from the center to either post should give a reading one way and nothing the other.

Please tell us if/when you find it.

Matt

Matt Colie wrote on Thu, 21 December 2017 15:11

Peer,

This is not any kind of a criticism of of your language capability. (Your English is much better than my German.)
The blue finned thing is the isolator and the round thing below it is the boost solenoid. Agree?
(Remember I have another '73 23' and know the issues well.)

Are you saying the the house lights stay on when you remove the cables to the outboard side of the boost solenoid, but go out when you remove the wire from the house terminal of the isolator?

Ken wrote: I question your diagnosis in that to have a failure that you are describing, it would take a double shorted diode in the isolator and no power being supplied by the house battery.

I have been straining to get this figured out and Ken may be mistaken.... (I never thought I would write that. - Either Ken)
If the alternator to engine battery went solid (as opposed to open) then this could happen, but it would require some creative rewiring as the terminal that is the central to all the 12V house is that post in the boost contactor. This would also make the alternator terminal hot when it should not be, but that should cause no other issues.

If the both diodes solid is correct, that is a very strange case. In all my years of 12V electrics, I have only seen one isolator diode go solid. These typically fail open when they do fail and that is just not common. And the rarely both fail. (Lightning strikes are another matter.)

I have to believe that that there is something there that should not be.

A simple test with a meter will confirm that the isolator has failed. An ohmmeter reading from the center to either post should give a reading one way and nothing the other.

Please tell us if/when you find it.

Matt

Matt, Here is what I was thinking when I wrote that:
He disconnects from the isolator and power goes away. He has no house battery connected at the time
so the power source has to be through the isolator. Now where is that
+12 volts coming from? With the engine running it could come through the
center terminal of the isolator. With the engine not running the center terminal
should be 0 VDC. Second path could be from the the engine side battery. This
would only occur if the isoltaor engine side diode was shorted. I now see what
I think is your point. It would take only ONE SHORTED DIODE on the engine side to
supply power to the center terminal and on through a good (or shorted) house side diode.

What I would to like to see is with the engine not running the voltage reading on the
isolator center terminal (should be 0) and the voltage on the house side isolator terminal.

I'm still thinking that he might have a wiring error somewhere. Metering the three
isolator terminals without the engine running might help isolate the issue. If there is
voltage on the center terminal. I would disconnect the wire on the center terminal
and read the voltage again. There are obviously other ways to accomplish the same thing.

Do not feel bad about calling me out on this. I have made many mistakes in my life
and I would rather have someone correct my errors than give out bad information.
That is why I got married twice. I once worked with a guy that was married 5 times.

Three of those times were to the same woman. Talk about mistakes.