What 3rd gauge?
 

Have a 97 manual truck and when I did gauges I bought a 3 gauge pillar since was same price as a 2 gauge and have had a pyro and manifold pressure gauge in but an empty hole for years. Thinking I wanna get something in there so trying to decide on what. Was thinking either fuel pressure, oil temp, or differential temp. Anyone got any suggestions as the next most needed gauge? I tow around 8-9,000 lbs with it regularly. Thanks.
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My vote is fuel pressure-it will pay for itself in saved fuel filters and great to trouble shoot when there is an issue with your truck,...

Second boost gauge.

Fuel pressure gauge will pay for itself very fast when you use it as an indicator of when to replace your fuel filter.
Using the gauge I've never gone less than 30k miles before having to change the filter.
Have gone as long as long as 62k.

i say both boost and fuel. mount the fuel on/under the dash somewhere

Another vote for fuel pressure. Why two boost gauges?

Fuel pressure--boost and EGT were my first three..

I Agree with all above. Fuel
BTW thats one neat lookin quad u got on that trailer.

One for each turbo.

My current manifold pressure gauge is a 100 psi fuel pressure gauge. I swap the connection to the other sending unit from time to time to check up on it, but 99.8% of the time, its my boost gauge. My old manifold pressure gauge (60 psi) is now my primary turbo boost gauge.

Cool, thanks for the input, I'll go with the fuel pressure gauge to fill that last hole.

Did some readying and they say a 12v needs a ~40 psi gauge. Being as I have autometer ultralite pyro/boost I wanted to stay the same style. I ordered a 60 psi water pressure gauge on ebay for a deal figuring fluid pressure is fluid pressure regardless of fluid type. Does anyone know any reason it owuldn't work with diesel? I also picked up a needle valve and will drill/tap the banjo on the inlet of the injection pump. Need to measure and pick up some braided line, will generic stainless braided brake line work for diesel or is the high dollar autometer stuff something special?

Your 60psi water gauge will work perfectly with the needle valve and that braided brake line will likely work just fine too.

Braided line is an overkill plus it tends to saw though anything it touches.
Just 1/8" nylon tubing like what is used for boost gauges is plenty adequate.
Air brake hose that most auto parts sell by the foot is good stuff.
Just thread it though some 1/4" hose to protect against kinks, cuts and abrasion.
Both my trucks have been using it for 15 years without one problem.

An analog clock is kinda nice...

Finally got everything all mounted and plumbed and seeing only 8-9 psi at idle and around 15psi at 2500 rpm. Fuel filter replaced and strainer cleaned last month. Overflow replaced this last summer just for periodic maintenance. Will double check overflow with the squeeze return line trick tomorrow and go from there I guess.