The presence of oil pressure is usually measured by whether the oil light is on or not.
The so called, idiot light, simply lets you know that the oil pressure is high enough to actuate the oil pressure switch and then the light.
The check valve (or check ball, respectively) opens between 4-6 psi.
So at all times, the pressure gauge should at least read that much as measured at the oil pressure switch.
If it is not showing any pressure you need to find out why.

Do not eliminate your oil light, this is your first and best indicator of proper oil flow. ¹⁾

Using the correct gauge means considering the gauge accuracy required at the pressure point being tested.
Low range pressure gauges will be more accurate on a hot engine when the oil is viscous and the pressure is low.
During a cold startup, the pressure will be higher due to thicker oil when cold.

Likewise, a 0-30 psi or 0-60 psi gauge will peg out on a cold startup which could possibly ruin the gauge.
But it will show a more accurate reading when the engine oil is hot and at low pressure.
Whereas a 0-100 psi gauge will be more accurate during a cold startup but less accurate during normal operation with hot oil.

Glycerin filled gauges will withstand more vibration than non-liquid gauges.

Oil Pressure Switch:
Oil is more restricted at the oil pressure switch than say at the rocker boxes.
So oil pressure will be higher when tested at the switch than when tested in the rocker box.

Rocker Box:
A Sportster does produce oil pressure in the rocker box: reportedly 3-5 psi at hot idle and 15psi+ on cold startup. ²⁾
Depending on the gauge selected, there may be little to no oil pressure registered on a high range gauge testing form the rocker box.
(the gauge may show some pressure when the oil is cool and thick but may not show any after 5 minutes of running) ³⁾
Due to the low oil pressure at the rocker box,
Don't get scared when you look down after its hot and its on zero. ⁴⁾

The FSMs for all years include suggested oil pressure figures for each model when testing.
Most FSMs suggest taking the oil pressure reading by removing the oil pressure switch and placing a gauge (or gauge line) there.
The exception would be 86-90 models (with a reference also to 91 models).
(where the pressure data in the manual was taken from the plug hole on the engine case between the tappets)
However, due to the testing points that are suggested, placing a gauge anywhere else doesn't help you match or verify oil pressure per the manual.
(or won't provide any relevant information that you can compare to the manual)
Some say an oil pressure gauge makes a nice back-up to the oil light though. ⁵⁾

However, you can fit a gauge in other places to simply show some pressure for peace of mind prior to each ride.
The gauge should show some pressure even if it's not to par with the manual.

At the testing points suggested in the manuals:
See Sportster Oil Pressure (57 to Present) in the Sportsterpedia for oil pressures per the FSMs.

Other reported pressures from XLFORUM members.

A 0-15 psi gauge (although it will max out with a cold motor) will give you the most accurate readings with hot oil. ⁶⁾
A 0-30 psi gauge is only useful at cold temps.
A 0-60 psi gauge is useless when testing from the rocker box.
All of this depends on the oil you are running also.

Multiple viscosity oils will show low to no pressure at running hot or cold idle.
50 wt in the summer shows lower pressure while 60 wt.

• 3-5 psi at hot idle.
• 15 psi+ when cold.
• 7-10 psi during normal riding conditions.

Other XLF member results noted from the rocker box:

• Cold start, running 20/50, - pressure off the scale at startup. ⁷⁾
  • Settled to 8-9 psi after a few minutes at fast idle.
  • After 2 miles, the pressure was steady at 12 psi.
  • After 5 miles, pressure dropped to 1-2 psi.
  • After 11 miles, pressure dropped to zero and stayed there.
  • When stopped at end of ride, it stayed at zero on idle.
  • Will see if the same thing happens at the weekend.

The oil pressure switch is directionally pointed differently on some year models.
For instance, 99-03 cases have the switch pointing down and 04-up is facing forward toward the frame slightly more so. ⁸⁾
So you may need to modify the parts list below to suit the positional needs from different year models.

Parts List:

• (1/8“) 90° fitting
• (1/8”) 'street tee' (for the oil pressure switch)
• (1/8“) 1-1/2” nipple 1/8“)
• (1/8”) pipe coupling
• (1/8“) 45° fitting
• (1/8”) pipe nipple(s)
• Teflon thread tape or thread compound

Thread the 90° fitting into the orifice that the pressure switch came out of first.
Thread in the tee fitting so that one port is facing straight out towards the left of the bike and the other port towards the front of the bike.
Test fit the pressure switch to make sure you have room for it before going any further.
Then apply the thread sealer and install it into the forward facing part of the tee.
Thread the 1-1/2“ nipple into the left facing port on the tee (with thread sealer).
Then add the pipe coupler and the 45° fitting onto the coupler.
The 45° fitting should be facing towards the left forward corner of the second cylinder.
Thread the oil line onto the 45° to run to the gauge.

A 1/4” thick aluminum flat stock can be purchased from a hardware store for the gauge bracket.
Cut off 4“ and drill 2 holes on each end.
Round one end and paint it if you like. ⁹⁾

Remove the oil filter and oil pressure switch. 10)	Install a 90° fitting where the pressure switch was. 11)	The fittings all together and ready to be put in place. (in addition to the first 90° fitting) 12)

2nd 90° faces down to mount the oil pressure switch. Measure to position the fittings so the switch is clear of the frame and engine case. 13)

According to the MoCo (FSMs), the oil pump is the prime testing point of oil pressure to the engine.
The procedure is to take the oil pressure gauge off and install an oil gauge there.
This works if you have verified that you do have oil flow to the engine and just want to check the pressure at the pump.
This takes the oil pressure switch as well as the oil light out of line.

However, as in the pics below, a tee can be added inline for a dedicated gauge.
You can either mount a permanent gauge to the tap or plug it off until needed.
This will keep the switch and the oil light inline and working if you need it.

Piping added to include the gauge and the oil pressure switch 15)

Remove the oil pressure switch from oil pump and install an 1/8” hose or tee fitting, then an 1/8“ the hose to the oil gauge.
Instead of removing the oil pressure switch out of the oil pressure chain,
You can remove it, install a tee at the pump, fit the switch to one end of the tee and the other end to the gauge.
This will keep the switch, and more importantly, the oil light in the loop.

Mount the oil gauge where it can be seen during operation.
You can use a flexible braided rocker box oil lines and mounted the gauge just off of the forward controls or on the downtube.

Oil pressure gauge on a 75 model downtube 16)

Oil pressure gauge on a 74 model mounted down low by the forward controls 17)

On some models there is a plugged hole between the tappets.
The plug was removed and a gauge was installed to measure pressure inside the case. ¹⁸⁾

This was done on the rear rocker box of a 77 model Sportster. ¹⁹⁾
With the engine in the bike, simply remove the rocker shaft end plug and screwed in the adapter and the gauge. ²⁰⁾
There is no need to remove the heads.

Use Foghollow adapter (H80409) or similar.
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The end plug was removed and replaced with a gauge adaptor. The gauge will be installed there. ²⁴⁾

The lubricated shaft was fitted back into the rocker box. Be sure that the spring and spacer washer are in place.
Fit the O-ring and gauge adaptor and lightly screw up by hand. You can use a bit of rubber grease on the O-ring to make it slide into the rocker box nicely.
Fit the aluminum shaft washer and dome nut. You can also put a bit of Permatex silicone on each side of the washer, as this doesn't spin once it tightened up. ²⁵⁾

Tighten each side a bit at a time so that you get the gauge mount oil hole in the right spot.
Tightening each side slowly allows the O-ring to slide into the rocker box and not catch on an edge.
Tighten to specs and wipe off the excess Permatex on that one end. Add a bit of liquid thread sealant on the gauge threads.
Make sure the angle of the gauge is good from your sitting position. You can back off the shaft nut and relocated the shaft if needed. ²⁶⁾