The 42VDC supply rail goes to the smaller 4-digit credit/ball in play display.
The 60VDC supply rail goes to the larger 6-digit player score displays

Gottlieb_Displays1.png

Pay special attention to the playfield coils the moment you start a game to see if any activate and lock on (stay activated). Immediately switch off if you notice any before F4 blows.

The playfield schematic below shows the coils and the voltages driving them. The computer controlled coils are wired to 24VDC, the non-computer controlled coils are wired to 38VDC (except for one mentioned below which is computer controlled).

All the playfield driven 24V coils appear to be extra fused with either a 2.0A or 2.5A fuse. However the cabinet 24V knocker coil and coin door "coin lockout coil" are not separately fused. Check them for short circuits. There are some relays on the playfield which are 24V driven but these aren't fused. Being higher resistance coils I wouldn't suspect them first up.

On the main playfield, the 38V driven coils are directly playfield switch activated. It could simply be that one of these playfield switches is stuck closed causing the respective coil to lock on the moment you start a game resulting in the F4 slow blow fuse blowing a few seconds later. These 38V coils are not separately fused so F4 is the only protection. Look at the very right hand side of the playfield schematic for these coils.

The lower playfield has a 38V driven coil "Up Kicker" that is computer controlled (by the driver board). This coil returns the ball from the lower playfield. Check whether it's locking on.

Yes, you should be able to.

The lower level and upstairs level pop bumpers are 24V driven - these pop bumpers are also 2.0A slow blow fused.
The two mid level playfield pop bumpers are 38V driven - these pop bumpers are also 2.5A slow blow fused.
Unless someones incorrectly overfused these, F4 shouldn't be blowing because of the pop bumper boards.

The flipper coils have two windings. One short thick high current winding thrusts the ball, the other thin long winding holds the flipper up. The hold winding is shorted by the End Of Stroke (EOS) switch on the flipper mechanism and opens when the flipper reaches the up position. It's in series with the thrust winding.
Without the higher resistance hold winding, the thrust winding would end up cooking the coil. So to measure the flipper coil resistances, you need to open that EOS switch (put some paper between the contacts).

Playfield_16.png

I don't know Haunted House's specific behavior but I wouldn't expect the knocker to activate when you start a new game. In most other games the knocker only activates as a notification you've won a free game.

I presume you should be able to stand the playfield vertically against the backbox (head) by pulling the playfield forward along the side cabinet rails (the playfield will be heavy). You'll then have better access to the relays where you can measure/adjust/clean the contacts.
Pressing the green flipper buttons, you should measure 24V when the U relay's active at the slate-blue-blue and slate-purple-purple wires which lead to the lower playfield flipper coils.

The "U" relay enables the lower playfield. When active the lower level general illumination (G.I.) lamps will illuminate so you can see the lower playfield, the lower playfield flippers will become enabled AND the top main level flippers will become disabled. This is to limit strain on the transformer by disabling flippers that are nowhere near the ball.
Note, the lower level G.I lamps are 24 volt lamps, not 6 volt lamps like the rest of the game. Installing 6V lamps in these sockets will cause them to blow.

Where the ball enters the lower playfield, there should be a switch that causes the computer to activate the U relay. When the ball returns to the main playfield the U relay should deactivate.

BTW, there's a Haunted House club thread:
https://pinside.com/pinball/forum/topic/haunted-house-club-the-beautiful-beast-all-welcome
At the very top there's a link to the clubs image gallery where you might find some useful reference pictures:
https://pinside.com/pinball/forum/topic/haunted-house-club-the-beautiful-beast-all-welcome?gallery#g

Sorry my mistake, it's the main playfield flippers (not upper playfield flippers) that become disabled by the U relay when the ball goes to the lower level.
See the U relay "break" switches in line with the main playfield flippers.

Playfield_U-Relay.png

Go into the switch test mode (look in the manual) and check whether the game detects the closure of each switch. Make sure you raise all drop targets and remove the ball from the game so you start with no closed switches. Find out if the switch to detect the ball going to the lower playfield is working.

With the self test button, step till #18 is shown in the credit display in the self tests.

After a second or two it should show "99" in the ball in play display provided all switches are sensed as open.

When you press any switch it's ID number will be shown in the ball in play display. The number remains until you press another switch.
If some switches don't detect when closed, determine if they're all on the same row or column in the switch matrix.