A couple of things:

I have a 1985 Dodge D100 with a Slant Six. I'm installing some aftermarket gauges (mechanical), which includes Oil Pressure, Water Temp, Volt Meter, & Fuel Level, and I am unsure of where and how to best install the Water Temp and Oil Pressure probe/sensors. My six is not equipped with AC. (To my sorrow.......it's been a very hot summer here in TN.)

If possible, I'd still like the original equipment "idiot lights" to function along with the new gauges. So will I need to "T" off wherever they're connected to the engine in order to achieve this? And if so, How do I do this?

As an unrelated issue, I have a water leak into the cab which I have thus far been unable to staunch. The water is entering from behind the instrument cluster on the extreme left side of the firewall. I can't figure out if it's coming in from around the front windshield, another source, or both. I have replaced both floor pans, and I'll be darned if I'm going to install new carpet until I solve the leak first.

Any help on these issues will be greatly appreciated!!!

Thank you very much!!!

for the oil pressure gauge, the existing idiot light sensor is at the rear of the oil pump, install a T there

for the water temperature, the best place to get engine coolant temperature is the top side of the cylinder head
in front of the thermostat housing. If you have replaced the lean burn ignition with an HEI you should have a
threaded port available there. Another option is to install the mechanical coolant sensor into the threaded coolant drain port
that is on the distributor side of the block, around #5 cylinder. A gauge reading from there will be slow to respond to
coolant temperature changes at the thermostat.

concerning the water leak, perhaps the cowling vent drain is clogged with leaves - debris and water is backing up in through
the driver side Ram vent,,,,

_________________
Doo Ron Ron and the Duke of Earl are friends of mine.....
https://www.youtube.com/watch?v=uX8Nj8ABEI8

Dear "Dad",

I really appreciate your input!! That was a great help to me!!! One last questions for you: What should the oil pressure read at idle, and what temp should the coolant normally be?

Many thanks once again.

~Muggins.....

You will quickly find that your options for gauge placement are very limited in the 81-up Dodge trucks. The best solutions I have found are these: https://www.glowshiftdirect.com/1986-19 ... leSelector

It says 86-93, but those will fit all the way down to 81.

oil pressure is somewhat dependent upon: oil viscosity and engine temp.
but anything above 10 psi at idle and then 10 psi for every 1000 RPM is a typical guideline
for a street driven vehicle of your trucks era.

if the temperature sender is close to the thermostat
water temp with motor through the warm up cycle should stay around the temp of the thermostat,
on very hot days and or with tough conditions, the water temp will go higher, depending upon
the condition of the radiator cap and antifreeze concentration it could go over the boiling point
of water.

_________________
Doo Ron Ron and the Duke of Earl are friends of mine.....
https://www.youtube.com/watch?v=uX8Nj8ABEI8

(1) CLICK ME

(2) pre 93 Dodge trucks are also known to develop cracks around the cowl area. See here and here and here.

Dear Mr. Reed,

Thanks so much for your input!! It's very helpful!!!

~Muggins