I know everyone gets all in a panic about mechanical fuel-pressure gauges inside the cab.
Mine, and any others I install, are always mechanical and plumbed direct, with fuel under pressure coming straight to the gauge.
The electric units are often inaccurate, although any gauge is much better than no gauge, and those fluid-hose extenders are way off.
Although diesel is not like gasoline, and a bath in fuel is more of an aggravation, than a danger, there are a few precautions that will prevent any fuel-spray disasters.
First, whether it be oil- or fuel-pressure, I install a 1/8-NPT ball-valve at the source, such that, in the event of a leak, I can shut off the valve and drive on.
Second, every fuel-pressure gauge installation requires a gauge "snubber", that absorbs the pulsations of the fuel-pump, and makes the reading steady, instead of constantly flinching with each stroke of the pump; without this "snubber", the gauge (and sender on an electrical unit) will not live long.
Third, use only good quality tubing and fittings, and some common sense in their routing; better yet is to have a braided stainless hose made for the run inside the cab.
A fuel-pressure gauge is probably by far the best diagnostic tool one can add to their engine.
Most other gauges can be done without and the truck live until the frame rusts in two.
Any fuel related issues are just guess work without a good fuel-pressure gauge.
Truck cranking but won't fire---is the gauge rising or laying on zero.
Engine getting sluggish---what is the gauge telling you.
Running fine, then dies all of a sudden---what was the gauge showing.
If only one gauge is installed, then put it between the filter and injector-pump, thus you can monitor how well the filter is flowing.
Better is to mount two gauges, one after the filter, and a second one ahead of the filter; thus, if pressure is low behind the filter, yet still good ahead of the filter, then you know that the filter is the problem; otherwise, one might replace a perfectly good filter when the problem lies within the lift-pump or plumbing.
I would spend my money on a fuel-pressure gauge before any other gauge.
