E30 Tach mystery

[liquidc3lls]

Hey guys, new to this forum read all the rules, did the search read every article i can find of help, and in conclusion i cant find an explanation to this mystery...allow me to elaborate,

I got my 1990 325i, a good 4 months ago, when i bought it, i had no speedo no tach and no mpg and of course the mileage does not work either except for the Temp (twitchy) and gas (fine), which i understand is quite normal for these cars, i know that i needed to check the grounds, maybe its that or the SI board or the Batteries. what i was planning on doing is finding out if its a "GROUNDING" issue first, or Batteries or the SI board....that was the plan.....today heading off to work, i turned the car on waited for it to warm up while i was prepping my coffee, its -28 in ottawa
.......once i got back in the car about to head off i noticed my Tach was working (twitchy) and my MPG is working(fine) but no speedo. I don't understand this because i have not done anything to make it work except unplug and re-plug the diff sensor 2 weeks prior, and it didn't work then...it just started to work out of no where, am genuinely very confused and with this new curve ball i don't know what and where to start from!
any help to clear this mystery would be appreciated just so that i understand what to do next in the hopes of fixing that speedo!

i do have an after market stereo from PO....i heard those can usually affect the cluster.

Thank you guys in advance

cheers
Happy new Years!

[Ceeker]

it can if the wires were butched to make the stereo work if they managed to strip some wrong wires. I suspect it is your SI batteries slowly dying giving their last breath.

[HavocSteve]

Have you tried swapping the Tach for a another one? Try that first. Also, check the grounds like you mentioned. Don't forget to change the fuses as well as blowing one of those will stop your Tach from working completely. I shorted the stereo in my E30 by accident and the fuse blown (If I remember it's #19). That's all the stereo will do lol.

[liquidc3lls]

i will go ahead and check that tomorrow, but yea like you mentioned Havoc, i did swap it with a buddy of mine he has an 325is 1988 it bascially did the same thing everything worked(gas) (temp) except the tach mpg and Speedo! just ran outside checked it and fuse 19 is intact