Ok, I guess I am getting myself confused here.
I found a 1992/1993 B3 Sedan with a 4 cyl gas engine with MFA. It is a Automatic (auto selector in tach). It has a DIGITAL ODO and MFA in the fuel/temp. It looks like the B4 VR MFA cluster. There is no analog odo or trip.
So I guess my question should be:
1) Can I use this cluster in a B4?
2) Can I swap the tach from the B4 NON MFA Manual Cluster into the B3 Auto Tach location?
3) Add 2 LED's (1 for glow plugs and 1 for MIL)?
4) Change the graphics for the tach to represent the lower rpm range?
5) Signal and MFA stocks interchangeable for the B3 and B4?
6) Change surround to match the B4 LED's?
If you're not concerened about maintaining 100% correct OE TDI graphics, this could be an easy conversion.
The MFA and tach should function perfectly and read correctly without modification and the only non- or incorrect-funcitioning item would be the MIL LED and, possibly, GPL LED.
SURROUND ISSUES
The B4 front surround trim can't be used with the B3 cluster because it has a complelety different contour at the perimeter where it mates to the cluster housing as well as a completely different attachment method. So, you're pretty much stuck with the B3 surround which, if similar to the B4 VR6 cluster in this regard, will cause the LED labeled MIL to be lighted by the ECU's GPL signal. I can't confirm that this will be the case because I haven't tried it (I do have a '94 B3 VR6 MFA cluster, but have never plugged it into my B4). If this is the case, you would have a mislabled GPL; not the end of the world and correctable by painting over the label if its bothersome.
By the same token, and like the B4-VR6-cluster-in-a-TDI scenario,the ECU's MIL signal likely won't have an LED to light (though this is unconfirmed with my B3 cluster). If that is the case, the B3 cluster has an unused and unlabeled LED on the left hand LED bank that should be able to be activated with some circuit analysis and subsequent modification. You cannot easily add an additional, 5th LED on either bank as you can with the B4 cluster.
TACH FACE
As previously stated, the B3 4-cyl. tach will function and read accurately without any modification. You will have too high a redline, of course, and if that bothers you, you can graphically modify it with a printed graphic or paint. The option to use the B4 TDI tach face with the B3 cluster is more problematic than it is when used with a B4 VR6 cluster. The B3 tach face locates and attaches to the tach differently than it does in a B4. In fact, internally, B3 and B4 clusters are constructed very, very differently (even though appear very similar externally). This isn't a big deal, though, its just a matter of drilling mounting holes in the tach face.
A bigger issue is that, because the B3 4-cyl. GL tach face has different tick mark spacing than the B4 TDI tach face, you would have to program a different value into the cluster controller chip's "program version" value to get an accurate tach reading and I don't think there was a B3 TDI or TD model from which you could retrieve the correct program version value, and I doubt the B4 TDI program version value would work because the B4 cluster is a completely different design than the B3. Whether or not you could obtain the correct program value for a B4 TDI tach face in a B3 GL cluster, it requires chip editing to change it. The guy who may be able to answer this question is member ChubsAuto, who has done many B4 MFA conversions in the traditional manner (i.e. B4 VR6 to B4 TDI) by reprogramming the chip, with great success and to much acclaim from club members.
If it proved impossible to do this way, the B4 TDI tach face could always be made to display accurately in the B3 GL cluster by splicing a pulse frequency adaptor into the tach signal as was done in MFA conversions before ChubsAuto began reprograming the controller chip to achieve display accuracy.
A disclaimer: I am not intimately familiar with all variations of B3 clusters and it's possible that a '92/'93 4-cyl cluster may differ from the '94 VR6 B3 cluster that I have (and haven't used) and the MIL vs. GPL issues might be different. Surround issues shouldn't be any different.
I hope, since you're taking the trouble to do this, that the cluster you found is a Canadian model which, I assume, your B4 is.
BTW, I haven't answered your previous questions, above, because those are not the questions to ask. The issues listed are the ones you need to focus on to make this work.
