Electrical dash niggles...

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MVX11V
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Joined: Tue May 30, 2017 11:53 am
Location: East Anglia, UK

Electrical dash niggles...

Post by MVX11V »

1) I've used the correct service resetting tool numerous times and it worked as it should, resetting the inspection lights and the oilservice light as it should. 2 years ago the oilservice light began to flicker quite brightly and then for a period, remained off until service time, or there about. The lights were all on for a few months until I could carry out a service day where they were all reset.
2 days later the oilservice light appears very dimly and has remained on since. What is the car trying to communicate to me with this random display of lights?

2) The MPG gauge works when it wants to, more off than on though. 9 times out of 10 it will work when I decelerate and then rest at 0 again when I press the accelerator pedal? What forces are behind this mysteriousness?
'HAUNTED :evil: ' and playworn 1986 635 Daily.
wattsmonkey
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Re: Electrical dash niggles...

Post by wattsmonkey »

If you've never replaced the SI board batteries, then they'd be my first suspects.
"Most of it necessary; all of it enjoyable." LJKS
'84 635CSi, dogleg...itbs and supercharger????? Eaton Mess
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MVX11V
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Location: East Anglia, UK

Re: Electrical dash niggles...

Post by MVX11V »

ooh, sounds exciting. I've never had a chance to get involved with the inside of this car because the outside keeps breaking! :mrgreen:
'HAUNTED :evil: ' and playworn 1986 635 Daily.
///Moe
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Re: Electrical dash niggles...

Post by ///Moe »

+1 on the SI board batteries, if they go bad you won't be able to reset the service interval lights, it won't store the data.

I had the same problem on my bmw's and after replacing the SI board batteries (they are solderet to the SI board inside the gauge cluster) they have been working as normal for years. I also resoldered a cracked soldering on one of the circuits and tightened the nuts on the back of the SI board gauge. They often get bad connection in this area, which could cause the temperature gauge etc. to flicker and sometimes not work at all.

Some fit a battery box elsewhere, outside the cluster with wiring to the SI board to make the batteries easier to replace the next time they go bad. Me personally, prefer to just solder them to the SI board as stock. I figured if they lasted 15-25 years they would last just as long the second time as well.

If you have the older type SI board they use two rechargable AA batteries, but it's important you get the right kind of batteries. A modern AA battery will most likely overload the (thin) charge circuits inside the cluster, because they charge faster than the original one's did.

They have to be Ni-Cd, as this is what the originals were.

I used panasonic batteries that I got from ebay and they work just fine.

But if you are really unlucky, the original batteries have started leaking and have destroyed the SI board, you won't tell before you open up the cluster. In some cases thr circuits may be corroded due to condensation of water inside the cluster (after all, it's really close to the windshield)

Hope this helps some :-)
E24 635CSiA 85' (garage queen)
E24 628CSiA 83' (turbo/manual?)
E23 745i 82' (turbo project)
E23 728i 86' (745i project)
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