Hi, I'm working on my mom's 1989 LeSabre. The instrument cluster was not working correctly, and I found that none of the ground wires at the connectors on the dash harness have any continuity to chassis ground. They all have continuity to one another but not to ground. I don't see any ground point under the dash where there is a ring terminal and a cluster of ground wires.

The manual I have is poor and simply shows each point going to ground with a ground symbol. No where does it explain where this is connected back to chassis ground.

Before I do any further unnecessary disassembly, could someone point me to a wiring diagram or some other document which shows where the main grounds are located on this car?

All of the black wires which are supposed to be ground at the instrument cluster are "floating" as if disconnected at one common point.

This car is the only "new" car which our family had. It was originally bought new by my dad's company in 1989 and used as a company car for several years. After that, it was bought from the company and remained our family car. It now has 533,000 miles on it. I just finished rebuilding the original engine after it was accidentally run hot. The plastic radiator drain plug broke and lost all the coolant. My mom didn't stop in time and resulted in damage.

The car is still all original matching numbers, with the original engine on its second overhaul and the 440T4 transmission having been repaired 4 or so times. The ground issue was pre-existing before the engine repairs. The reason the overheat warning was not taken seriously is because the instrument panel was doing all sorts of other wrong things, and mom though this was part of the instrument problem. She ended up driving about 25 miles without coolant.

It's been a bad month for our cars. I was rebuilding this engine when the timing chain failed in my 87 Park Avenue coupe.

Thanks in advance for any info on the wiring ground locations.
Sincerely,
David

Well.... I found the problem thanks to another enthusiast.

There is a one-circuit Weatherpack connector at the battery negative terminal. It seems to be the negative reference for the instrument cluster. While it was open, turning on the headlights and more specifically turning the instrument panel lights to full brightness, would cause the speedometer to stop working and the turn signal indicators to both illuminate.

Reconnecting this solved it. My mom said that after she had a local DIY auto parts quickie shop put a new battery in, the speedometer has been intermittent. This makes sense since they probably dislodged this wire.