speedo and tach calibration?

[Blaizefed]

Right, Just bought my 86 westy. Been working out the bugs, and one of them is the gauges both being out of whack.

First, the speedo is off (I know they all are) but its way off. 10MPH on the freeway. I have however noticed it sits at about 8 mph when not moving. So I presume the best option here is to simply pull the needle off and put it back on in a different place? As this is a german import, and therefore would have had a KMH speedo, someone has clearly been in there before.

Next is the bigger mystery. The tach is low. Very low. Idle reads at 300 rpm or so, and 60mph (actual GPS MPH) is reading 2000 rpm. Now that can't be anywhere close to right. Its a jx diesel, with a 5 speed. So should be up around 3400 or so at that speed right? Now when I bought it the speed sensor wire at the tach wasn't even connected. I presume this was to silence the oil buzzer. Also the high oil pressure sensor was wired to a mystery wire (not part of the std harness, haven't figured out where it goes, but not connected to anything now) and the wire meant to go there was cut. Thats all repaired, oil light now works as it should.

Also, when i start the bus, the tach doesn't work, and the battery light stays on till I rev the engine fairly high. say 1800-2000 rpm or so. Then it jumps to life, and the batt light goes out.

Now I am the 3rd owner, and the 2nd UK owner. Whoever the 1st owner back in germany was, he has mucked around with this thing. I have 3 auxiliary gauges in the dash (tim, amps, and volts, so nothing really useful) and I have an intercooler bolted in over the gearbox. Not connected to anything, but its up there, so something fun was happening at some point.

So, what do we think? have I got the wrong tach? did it have a TDI way back when, he took it out, and left the tach but just didn't connect it? Do I have the wrong alternator? is there a difference? can the tach be adjusted? Any ideas?

[Oldiebut goodie]

The tach will not show on start up because the revs aren't high enough for the alternator to begin charging (hence battery charge / status light being on). A lot of the alternators are like that mine is like that on my van and also the same on my boat.
Someone else may be able to help with the tach. (I only have one in my boat which is a good way of telling when the bottom needs scraping as I can't get full revs with a dirty bottom )
Speedo can be sorted - some have a mark on the dial below the stop where the needle should be fitted and it is then gently lifted over the stop giving a little bit of pre-load on the spring. Worth looking for that mark.

[CovKid]

Speedos are indeed notoriously inaccurate and the nearest I've got to accurate was when I fitted much bigger wheels and tyres. Now its at least reading correctly up to 50mph but theres not much you can do other than fitting something more modern with a suitable sender but even then some degree of calibration is required. Other than that, GPS will give an idea of what speed at what needle position as a useful reference point. The lazy alternator can be fixed (usually) by replacing diode pack (not regulator) inside but invariably it will return to being lazy. I just give it a rev automatically now. Its easier than taking the alternator to bits anyway.

My tacho appears to work correctly but there are quite a few threads on other forums that detail the internal circuit board. It sounds as though one of the components has gone out of spec giving a false reading.