Mentioned somewhere my mistrust and disaffection for OE instruments, geared to provide minimal relief to unwary drivers, and in the case of the P38's ECT, downright scary - having the Nano reach 117 and the needle isn't moving because it moves after 120 is worthy of distateful words for whoever designed it that way.
I always thought of getting some extra info, I reutilized my old Scangauge and fitted it where the front ashtray is, and use it to monitor IAT and ECT more precisely (at least I know better when I am going to blow!), along with fuel calculations for trip computer, VLT, etc. But this is not enough.

I have a battery of old school VDO gauges I was going to fit to my HZJ laying around inutilized, but they barely match the clean shapes of the P38 cockpit, so I decided to settle for a more sober look and just put something small where the rubber mat sits in the dashboard, and just fit up to three gauges. Now is where the fun starts.

1) has anyone ever installed or seen anything installed there? Having the dashboard out (all peeled off, I had a lot of fun with the glue!), I would like to drill and run all cables while everything is accessible. I've noticed the dash center indentation where the mat goes fits fairly well a mini MudPod, which does fit three gauges and has a similar "grain" finish to the top of the dash, ok, but the underside is taken by the ducts of the HeVAC, there is not much room to manouver. Any opinion before I drill carelessly? :-)

2) to minimize the mess but maximize the info I found that the Madman EMS is a nice pretty package, recommend you look at it. Price is hefty, but has a lot of inputs. Unfortunately, the EMS2 is out of production, its black/green dial was perfect to match the rest of the dashboard. The new EMS3 is full color like those Japanese aftermarket radios, but that is what it is. Inputs are VLT, EGT (I guess don't need this on the V8 at the time, unless I go S/C), CLD (Coolant level), ECT (Coolant temp), Oil pressure (or Boost), Oil temp, and up to 2 outputs where via relay you can activate something else, for example the condenser fans.

3) Now, I got all the wiring for the MadMan and I am wondering where to attach myself to. I will run all wires to the engine bay, but leave the EGT disconnected at the time. My plan was to wire:
a) Oil pressure - what to use? there is like no place to fit one around the filter, maybe one of these "sandwitch flanges" that fit in between filter and block?
b) Oil temp - not sure yet usually the suggestion is a plug in the sump, either drilling, or replace the sump plug with one with the sensor. I do not like any of these ideas, so I thought the following: the gearbox cooler has a temp sensor on the side (more on this later), what if I fit one to the engine oil cooler and monitor from there? I am planning to take the gearbox cooler sensor out of my donor Rangie and run it with a tester to see what response it provides ....
c) Coolant temp is fairly easy, I will select the hottest point - I think is the top hose - to have a separate reading from the sensor that feeds the Motronic (and the Nano or the Scangauge in my case). 2 readings is better than one!
d) Coolant level is also easy, I had a mate in Italy done in his D2, using BMW expansion tank with provision for a sensor and a sensor itself, wired accordingly
e) back in the day where every hot day was a dat of terror, I've spliced into the switch for the condenser fans to have the possibility to activate them manually. I will now wire this switch to the MadMan relayed output, to have the gauge directly activate the fans once a worrisome temp is detected.

Since I am not a master in electrics, anyone that wants to throw a suggestion on this ... be welcome - even a "why are you bothering?" but I have already passed that stage :-)))

Will write later about the other auxiliary gauges I am planning ...

For oil pressure you could use something like this https://www.carbuilder.com/uk/stainless-steel-18-npt-adapter between engine block and pressure switch and fit a gauge sender in the extra hole. You are aware that you can adjust the reading on the temperature gauge aren't you? It is what would normally be termed a compressed scale gauge so only reads over a limited range. Mine is set to reach the red at 105 degrees. There's trimmer pots on the top of the instrument PCB that allow you to adjust the offset and slope for the speedo and tacho along with the reading for the fuel and temperature gauges.

Which BMW header tank do people use. I read a post from Dave3d on the dark side where he suggested a BMW E34 header tank but when I found that one (here http://bmwfans.info/parts-catalog/E34-Sedan/Europe/M5_3.6-S38/browse/radiator/expansion_tank/) it appears from the picture to be a mirror image of ours.

i'm still "dash off" too... on the indentation on the top of the dash - there's the soft skin - and a layer of ABS straight under which would take a self tapper. If you drill it and self-tap it there's no reason why you should have an air leak (any more than every other join in the ducting), but you cd add some RTV if it was a concern. However the windscreen edge is a lot clearer than the cabin edge if you're drilling blind. I think i'd be tempted to use a good double-sided tape. The wires can come up through the centre vent, and follow the same route as the alarm/ sun sensor wiring

While not as satisfying as a bank of aux gauges, the torque app and a bluetooth OBDII connector will give you the actual readings the sensors are seeing. If you have a phone mount in your P38 it's really handy for seeing information while on the move and can even graph outputs for later examination.

I do already have the Scangauge taking stuff from the ODB port to give me a number of readings available from the Motronic, that would be Intake Air Temp, Engine Coolant Temp, Timing, Throttle/Engine Load (with calculated Horse Power and Torque Request, I assume this is part of the data exchanged between engine and gearbox), some consumption calculations (instant and average, liters per hour, etc.), fuel loop (lambda control), MAP, RPM, km/h, TPS position, and that is it.
What I am after is info not provided as part of the "standard" package, or that the Scangauge can't read/obtain. Does the Torque app offers more on the P38? I have a mate that use it with great satisfaction, I could ask him to plug it in ... but it is very basic.
I will go along other data in later posts ... one thing at the time!

For oil pressure you could use something like this
I like it! Will get one and fiddle with it! I already have the two sensors just need to fit them. Next oil change ... cool!

You are aware that you can adjust the reading on the temperature gauge aren't you?
No, I was not aware of this and I would have not even imagined such thing possible except with physical adjustment or electronic calibration with sophisticated equipment ... this is very interesting. I will fish the instrument panel from the rubble in the garage and will open it up - I want chrome 'bling' surrounds on the instruments, can't help myself lol :-) - and will check for that ... if you drop a line or two on how to make it it would be great!

Which BMW header tank do people use.
I do not know for what model exactly, my mates in Italy use for the D2 the tank BMW part no. 17111712641, same dimensions as the LR one. It fits perfectly, but have been told you need to fiddle a bit with the lower pipe or put some spray grease to help it fit in. I have bought it (new, don't want to risk a secondhand one) for around 50 euro.
The level sensor is BMW 61311384739, I got a Febi/Bilstein for like 10 euro.
If you are good with electrical/wiring you can make your own connector, I just went to a guy I know that breaks BMWs with the sensor, and he cut me the appropriate plug from one derelict 5er. I like clean looks ...

Sorry I made a mess in the post above tried to fix it couple time but I am making more mess ... well read more carefully, sorry! :-)

i'm still "dash off" too... on the indentation on the top of the dash - there's the soft skin - and a layer of ABS straight under which would take a self tapper. If you drill it and self-tap it there's no reason why you should have an air leak (any more than every other join in the ducting), but you cd add some RTV if it was a concern. However the windscreen edge is a lot clearer than the cabin edge if you're drilling blind. I think i'd be tempted to use a good double-sided tape. The wires can come up through the centre vent, and follow the same route as the alarm/ sun sensor wiring

Not so much worried about drilling or air leaks, problem seems to be that the heater box with its dreaded motorized flaps sits right under the indentation ... if the instrument pod is fitted offside no problems, but the way it is ... I need to bring them close and make a few measurements, once the snow melts. The windscreen end is too far away, the MadMan uses buttons to switch through the inputs ....
Wires from the centre vent! From the top of the dash! Horror! lol :-) I avoid cables on sight whenever possible ;-)

Some photos I managed to make to show what I am trying to figure out for the instrument's placement ...

And this is the "inner" part or underside of the dash, where it meets the heater box.

And the heater box ...

EDIT: I manage to make the quick links work directly as images! I knew was not (so) dumb!

Bolx to clicking on all those links lol.

There you go, fixed! In any case before drilling I wait to see if I can get suitable senders!

Next in line: transmission temperatures!

I've noticed both gearbox and transfer box are fitted with temp switches, which conveniently provide the BeCM temp data of some sort, which conveniently is not provided to the driver except by the "OVERHEAT" message and associated dings and dongs.
Now looking at the ETM from the transfer gearbox comes out from switch X174 the signal, and from the oil cooler is the gearbox temp signal. Both go only to the BeCM and instrument panel. I am thinking both are useless to hijack it since probably are dumb off-on switches, but since SPA design offers a twin temp gauge which looks made to match the green on black LEDs in the P38, why not get both data in.
Now, I haven't, but has anyone else seen an auto temp gauge on a P38? Am I going to be the first one? :-)

I fitted a gearbox temperature gauge to mine when I fitted a HP24 box. I got Ashcrofts to weld in a pocket into the gearbox sump pan.
I cannibalised an aftermarket gauge and mounted the LED readout in the dash behind one of the unused black sections.

Ran it for many years then it packed in and I couldn't find the same type. Must revisit the project.

It was really useful towing.