hi,
I have a 1984 242 glt turbo with a rather strange problem
regarding the tach and instrument cluster lamps. I was replacing the
clock and accidiently shorted one of the power leads ( either the
one for the clock or its lamp I'm not sure). So I replaced fuse
that had blown. But now I measure no voltage at either the lamp
or clock power terminals. In addition all instrument lights
except for the turbo guages don't come on. I tested the bulb
in the clock and it is still good. So I'm wondering if I maybe
I shorted something in the circuit board of the cluster?

I used a voltmenter on the three terminals in back of the tachometer
which provide power to the clock and it's lamp. All read no voltage(except for
the ground which is still fine). In addition
what is even weirder is that when I turn on the head lamp switch
while driving, the tach drops to 0 unlass I turn the dimmer to
the lowest. Regardless the dash remains dark but the tach won't work
unless the dimmer is at it's lowest.

I don't think the dimmer is broken because the turbo guages still
light up an dim. According to the manual they have a seperate connection
to the dimmer, while the clock and the instrument cluster are all on the same
connection. Anyway I hope this makes sense. And any help would be greatly
appreciated. I think I just need a new cluster or circuit board as
everything else seems to check out. But I'd appreciate any suggestions in this
matter.

Thanks,
Drew

I think you'll find a short piece of foil missing on the circuit board. If you pull the cluster out, examine the board under good light, use patience, you will see the break. Not sure about the 84, but the thin trace on the 89's circuit board is right around the tach.

It happens a lot, because the clock is powered with the key off.
--
Art Benstein near Baltimore

thnx, that sounds like it just might be it, i'll open it
up this weekend. However after today's drive my car's got
few more quirks. The warning buzzer(for keys, lights, and doors)
is now on all the time while the car is running. Could this be
due to the that shorted trace on the circuit board as well?
and as far as the insrument cluster lights not comming
on can I assume they where burnt out when I shorted the clock's power
lead? Are those bulbs easy to replace?

Thnx

Lights are easy to replace, you'll see em once you pull the insturment cluster. Did they burn out? possibly. When I shorted out my clock circut, I only had that strange tach issue of dropping to zero with the lights on (and non clock of course). But, if I turned the dimmer down, the tach came up. No idea about warning buzzer issues. I guess see what happens once you repair the circut board and go from there. BTW, the bulbs should only cost you $2 or so for a package of two. I once paid $9 for a rocker switch bulb from the local dealer. Never again!

Good Luck...

Art's right on. Here's a pic he sent me a while back. The short was only about 3/16" from the arrow in the pic. You have to disassemble the insturment cluster quite a bit, removing guages and such. Then some small parts soldering. Took about 45 min.

http://www.brickboard.com/RWD/index.htm?id=588869

1987 245DL 229k

The only thing I can think of is to check the resistance from the negative terminal of the tach to a good ground. It should be close to zero. I doesn't look like the voltage stabalizer is involved in this. The gas and temp guage still work, right. Fuse 8 and 13 OK?

yea the fuel and temp still work. Fuses 8 and 13 still look intact.
I'll try testing the ground terminal later today. So the for the tacjh
I can use the ground on the back of the gauge?

Sounds like the other posts might get you fixed. But if you still need to check the ground, check between the negative of the tach and chassis ground for close to zero ohms. If it is high then some etch on the circuit board is likely fried.