In the SIII it is pretty simple.
The SIII(the SI & SII may be similar) has a metal plate that supports the dash. This plate is what all the gauges & lights ground to. This causes a bit of a problem when installing after market gauges, but fear not there are PLENTY of ground spots available. One in particular is attached to the plate via a spade connector between the coolant temp & fuel level gauges(I did not get a photo of it). So besides running new grounds, installing gauges is a snap.
The gauges I used were Auto Meter Sport-Comp. I feel they give a better look while not standing out pf place. The size is 2 1/6". You DO NOT want to go bigger because unless you like cutting your wood dash AND the metal plate, they just will not fit. the 2 1/16" are an exact fit as standard.

Getting out your old gauges is pretty easy. You push in & turn your speedo & tach. They com right out..then unplug & move. Undo the lower beauty panel(under the steering column). With this panel removed you can reach up & unscrew the original gauges. It may take some fiddling but if I can do it, it should be easy for a skinner more limber person.

The gauge holder will need to be cut down, because of the thickness of the dash in the SIII. Not a big deal & takes all but 5 minutes with a hacksaw.

The old gauges will have a RED/WHITE stripe wire for the light, a sender wire & a GREEN power wire(except the Voltage gauge of course). One will be male spade connector the other a female spade connector. Remember which one you want to take off as you will need to transfer a srew-on connection from the original gauge to the new gauge(if you want to keep it easy & reuse the original wire).

As for the ground, you need to find one for the gauge & light. I just piggybacked the light ground to the gauge ground & ran one wire. For light POWER, you can use the RED w/WHITE stripe wire. I just cut off the old socket, as seen in the pics.

It really is rather simple. If you want to update the look & get a more accurate gauge. I will also be doing the speedo & tach.
If you have any questions just ask.

Will post up tomorrow about the sender unit install.

 

Hello. Good start, and please post more pics I'd like to see how the other gauges look in there and a group photo of the whole dash.

One question, may I ask why you are swapping the gauges out? Just curious.

Thanks and good luck!

Eric

 

I will get more pics, no worries on that. Should be up late tomorrow. I will still have the old volt gauge in there as I did not get it yet,plus it REALLY shows the difference.

I am swapping out the gauges because the fuel gauge only worked when it wanted to, which didn't matter because the rest of the fuel system, with the exception of the fuel pump & injectors didnt work. The coolant gauge & sender didn't work. The only gauge that DID work is the oil pressure(the Speed & Tach do work).
Plus I am giving the car a more custom makeover.(Did you see my fuel cell thread?). I made full LED lighting for the tail lights & turn signals, also for all the lighting in the cabin. I am also redoing the dash & center in a dark burlwood & stainless steel accents.
It has been a BAD case of shipwright's disease.

Sometimes with this car I feel like.....

 

A few more pics & some info.

The fitting that come with the temp sensor will not work with the stock coolant rail. I hollowed out the original sender unit & epoxied the new sender into it. Reason I did this is because there is no one in Panama that has the proper adapter.
The oil sender unit supplied with the gauge is a direct replacement from the factory unit. Just have to put on a new connector.

Will try to post more pic slater. But like stated it is fairly easy to do & I just wanted to get it done.

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Here is the hollowed out original sender & the sender I just had to replace. This was a new sender & worked fine, just not the proper one for this gauge.

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Nice job espresso. The Daimler version (exactly the same but for a bumpy grille) had the bezels painted silver. Easy to do with a steady hand. Did you have difficulty matching the output on the gauges so they read accurately?

 

Well for fuel I used the GM 0-90, well because.... I have a fuel cell.
As for the water, I posted pics of the sender & for the oil I just unscrewed the original sender & the aftermarket sender screwed right in place of it.
The hardest part is having to cut off a few old connectors & add new spade or o-ring connectors.