The scenario: 10+ years of perfect service from the 12v system. During recent trip, while using lights/fans/pump, I fired up genny for microwave use - everything was working fine. When I shut down genny, the whole 12v system went down with it - no lights/fans/pump/12v recepts. Fired genny back up and 12v came back online. Tried the same thing with shore power - same results. 12v system works as long as I supply 120v, but won't operate on its own.

Checks so far (performed by admitted electrical illiterate):

1. Coach battery tests 12.7v at rest - battery ground "appears" good.
2. No load transfer switch - just old fashioned either/or plug for genny/shore power.
3. 12v fuse panel shows good fuses - all test OK on both sides of buss (continuity only)
4. Nothing changes when chassis battery brought on line with coach battery
5. When hooked to 120v, PD converter indicates all cycles (charge/float/desulfate) are operating
6. All 120v breakers appear OK & set.
7. Cursory look at under belly wiring - no breaks/abrasions/disconnections observed

Summary: I'm stumped - Any thoughts & suggestions appreciated

Lee, I think your problem is in your converter. When running off 120v the converter supplys your 12v. I think the relay to connect back to the battery circuit must not be making contact.

Check 12v from batteries to converter, then 12v from converter to 12v fuse panel. This is the way my 76 is wired. My 86 does not use a transfer relay.

After looking at PD website. The 12v does not transfer thru their unit. I would look for a open between batteries and PD converter. Does your 12v to your converter come from your gen. lugs? Is there a breaker in line there?

Older converters are dual-output. When 120VAC is present, a relay powers the 12VDC direct from the converter. When 120VAC isn't connected, the relay switches to the battery.

I suspect the converter also.

Yep, it was the converter alright.....Replaced
and back in business. 6 years on a new PD9245....I woulda thought more lifespan than that.......My genny might have spiked to cause
the problem, but PD claims the unit protects itself from that....Oh well....Thanks for the advice guys....On the road again....

I would guess there's more to it than that. The 92xx series is single-output, that is 12VDC always comes from the batteries and the converter when plugged in (the converter basically acts as a battery charger). The batteries are always connected unless the 12VDC master is off.