Instrument Cluster and Gauges

Normal Instrument Ranges: Left to Right:
Anything below an indicated 13v off-idle is trouble. The first thing to check is fuse #5. If its contacts are corroded, it can cause a low reading. The next thing is to go through the grounds, especially the one up front. Finally check the output of the alternator with a meter connected to the "Jump Lead Starting" post in the engine compartment and grounded directly to the frame or engine block. The voltage should read between 13.5 and 14.5 volts with the engine running. The battery icon on the dash must light when the key is turned on and go out when the engine starts. Some people have replaced instrument cluster illumination bulbs with LEDs - this bulb must remain incandescent in order for the alternator to function!
NOTE a slipping alternator belt can cause low voltage at high engine/car speed. See the  article on Alternators for how to check the belt tension. This is very important!
Most cars will operate normally between the "160" hash mark and the 220 indication. Anything less usually means that there is no thermostat and the weather is cold or  fuse #5 needs changing. Anything more is big trouble. Be sure the coolant system is free of air and the fans are coming on. If the needle reaches the red portion of the gauge, turn the engine off immediately.
Occasionally a voltage surge will cause the needle to stick pointing straight down. This can often be remedied by (with the car running) slapping the left side of the binnacle with your open hand. If this happens often, you probably need to clean up ground connections (article coming). 
The speedo should indicate the velocity of the car within 10%. It can be calibrated by a shop that specializes in this. Original speedometers indicated from 0-85 mph, although the car is capable of higher speeds. DMC sell an upgraded instrument that indicates to 140 mph. Cars destined for sale in Canada were equipped with speedometers and odometers calibrated in kilometers. The speedometer drive is a mechanical link to the left front wheel. If the speedo quits, check the Speedometer Article for more information. This article also discussed the trip reset knob function and repair. 
The tach indicates the engine speed in revolutions per minute [rpm]. It is fed by the same signal that pulses the negative side of the coil and that furnishes the tach/fuel relay with its interlock signal. The tach itself is an electronic device that swings the needle in response to the frequency of the digital signal it receives. If it stops working, or reads backwards, and nothing else is wrong, simply replace it. Erratic behavior can indicate high resistance in the chassis ground circuit.
Normal, unmodified, PRV engines run oil pressure that is quite high. About 80 psi off-idle at any temperature. Hot idle won't be much lower-60psi or so. Any engine that has had the heads off and cams out may run a little less. Anything below 40 psi off-idle is rare, but not yet dangerous. Very low oil pressure-less than 10psi- can cause the cam chain tensioners to back off and the chains to howl. The warning light comes on at 5 psi. The gauge sender is located on the passenger's side of the engine near the oil filter. A reading that is constantly maximum or slow to move is probably the fault of the sender, but can also be impacted by corroded wiring connections. The original senders (marked AC) often read high and can be very jumpy. Replacement of the sender will cure this. 
The Oil Light is controlled by another pressure sensor switch on the driver's side just in front of the AC belt tensioning bracket. It rarely malfunctions but it does often leak. This light should illuminate with the key turned on and go off as soon as the engine is started. If this light ever illuminates with the engine running, TURN IT OFF immediately and check for wiring shorts at the pressure sensor by disconnecting the wire from the sensor. If the light goes off with the sensor disconnected, there is probably a genuine internal oil pump failure that must be repaired before running the engine. 
Fuel Gauge and Light
A float-type sender in the fuel tank controls the gauge. Most erroneous indications are the fault of the sender. The original senders were pretty flimsy and can be identified by their yellowish color and plastic manufacture. Many have failed and been replaced with the reproduction from DMC, identifiable by the silver metal tube and black top with the "" stamped on the top. A properly functioning original sender will light the low fuel light when 1.5 gallons remain. On the DMC replacement, the low fuel light will illuminate and stay on when 2.5 gallons remain.
If you are bringing a car "back to life" and replacing the internal fuel tank components, read the Fuel Tank Contamination Knowledgebase articles and consider installing the Fuel Pump/Sender module for a more accurate and longer lasting fuel sender.
All gauges other than the speedometer can "float" or be in inaccurate positions until the key is turned on.
Lambda Light  See related article.
Brake Light
The brake light can indicate two different problems. The light will illuminate if the parking brake is applied, OR if the brake fluid in the master cylinder reservoir is low. To verify which one is the problem, disconnect the wire at the top of the brake master cylinder (check the fluid while you are at it). If the light stays on, the parking brake is probably not released all the way. 
Written by Warren Wallingford with edits by James Espey, DeLorean Motor Company (Texas)
Revised 1/13/2022 ET (formatting and links)