A voltage drop from 12.5V to 10.3V under load indicates excessive resistance in your headlight circuit, likely from corroded connections or undersized wiring. This significant drop explains your dim headlights and requires immediate attention for safety.
P0171 and P0174 together indicate system-wide lean issue. Most likely intake manifold gasket, PCV system, or MAF sensor. V10 known for PCV elbow and intake gasket issues. Smoke test recommended to find vacuum leaks.
For exhaust manifold gasket replacement with broken studs on your 2003 Fleetwood Southwind in Waukesha, WI, contact specialized RV service centers or heavy-duty truck repair shops. This complex job typically requires professional expertise when head removal is needed.
Power remaining after key removal indicates failed ignition switch or stuck relay. Test for voltage on run circuit with key off. Check for hot relays in fuse box. Ignition switch replacement is straightforward if confirmed as cause.
The fuse panel diagram for a 1994 Southwind motorhome is typically located on the inside of the fuse panel cover or in the owner's manual. If missing, you can create your own diagram by testing each fuse with the electrical systems.
For your 2005 Southwind with 400W solar and 4 6V batteries, upgrade to a 2000W pure sine wave inverter like the Aims Power or Renogy models. A 2500W unit may strain your battery bank unless you upgrade to lithium or add more lead-acid capacity.
Without seeing the picture, that dangling 'gizmo' near cylinder #5 on your 2000 Ford V-10 is likely a vacuum line, wiring harness clip, or emissions component that's come loose. The Ford V-10 has several small components in that area that can work loose over time.