Hi

I looked at the clock wiring for the 89 740
The - side is common with the Tach and the Instrument lights.
You can check for an intermit gnd connection at the cluster
between clock and tach and flex the board etc .

The + side goes to "30+ supply" a Green red wire back through a junction
"32/4" and to the fuse block 7 pin rail between relay socket C and H.
You can poke around those wires and look for a loose connection or flaky
lug.

I found a lot of loose spade lugs and a few suspect wire lug crimps at the
fuse block. I sense that many buggy electrical problems may be due to loose
lugs at relay sockets as well. This may be from people yanking on the relays
and opening/looesening the pins at the relay sockets. I'm looking for a source for those pins that have a locking tab.
A light smear of dielectric silicone on the connections might help delay corrosion.

Good luck, Bill
Good luck,