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i have a question regarding the yazaki speedo clusters versus the vdo units.
as some of you know i am the proud owner of a 1986 740 wagon with nearly 300,000 miles and still running strong. well i went to look for a diffrent instrument cluster at the wreckers and i found a 1987 sedan that had the yazaki cluster that matched up to my wiring(3 pins on the wire below the speedo not 4 like the newer ones)
i have the vdo setup in my 740 and was told that yazaki can be used also so i figured why not. well the issue here is this:

the speedometer, rpm meter, od and fuel gauge all work fine. no issues there
the problem is that the temp gauge goes all the way to the far red and fluctuates as i start the car up. also the a/c clutch circuit gets "shorted?" out with that cluster in place. how would i fix the cluster so that it will work perfectly. i hooked up everything exactly the way its supposed to be. also there is a check or system check light in the yazaki cluster that dissappears after a few seconds.
maybee there is a diode or something on the flexboard that needs to be cut out or switched?

any help would be greatly appreciated. you dont know how much of a pain it is to get a cluster thats appropriate for my 740 ive tried many sources and cars to no avail. and finally got something i can work with. also if any other parts are needed tell me so i can pick them up on friday.

thanks,
geoff