1990 temp gauge & tachometer, electrical

[ChrisWhewell]

The temp gauge on my 90, AND the tachometer, both fail simultaneously.  Then, a moment later, they both come back.  Then, they both fail again, intermittently, but simultaneously, always.

Apparently they're joined at the hip.   The problem is that its 103 degrees today and after much BS, I had finally gotten my AC system operational.   Except, when the tach and temp gauge fail together, the AC compressor won't come on.   Before I do a frame-off restoration trying to hunt it down, please, I hope someone can maybe point me to where these two gauge features might have a common circuit..... I've already cleaned the two grounds up by the battery and cleaned all the contacts, so that's eliminated....    Thank you for any insights

[ChrisWhewell]

Here's one, the guy had the same issue:   http://reattaowner.com/roj/kunena/reatta-community-forum/944-new-to-reatta-site-and-reatta-with-a-question

[padgett]

First thought: is the cap with the jumper that says "do not remove" on your ALDL plug ?

 

Next I'd display  BD60 (Vehicle speed read by the BCM) and see if it fails at the same time or not. If it does, check ED12.  (see VSS wiring in 8A-33).

 

Built in diagnostics are great but for more than one data point at a time, you need a real computer.

[ChrisWhewell]

No, there's no cap on the ALDL socket, it is missing.  Darn.   Is there a cheap fix, like jumper a wire between two points ?

 

Thanks so very much 

[Machiner 55]

Chris,

I believe our Technical Advisor also lives in or around Georgetown, TX.

His name is  Barney Eaton

He may be able to help with finding you a new cover for the ALDL connector.

 

John F.

[Barney Eaton]

It is probably a problem in the cluster..........I have a couple of spares we can try if you want to do that.

I am dog sitting this week so next week would be better......just give me a call.

[ChrisWhewell]

Thanks Barney, will do.  I just met one of your friends up at O'reillys, the chem. engineer dude who does forensic accident recon.  Small world ....   I went out to Gabe yesterday, got the ceramic window tint installed.   Wow, I'm impressed how it blocks infrared, the mfr. claims 70% screening.   Cost a little more but worth it.

[Barney Eaton]

Well...I try to make friends with smart people.   I can always drag them down to my level, but I can't fix stupid.

[ChrisWhewell]

Whatever its worth, and maybe a clue..... the tach stops first, then half a second later the temp gauge quits.  Sometimes the tach goes out and comes back on so fast, the temp guage doesn't have time to stop functioning.   So, the both don't fail simultaneously, it might seem as if the temp gauge failure is predicated upon first the tach reading stopping

[Ronnie]

I would check all the grounds behind the battery.

[padgett]

+1 on probably the cluster but can display both the tach (ED 11) and coolant temp (ED 04) with the diagnostics. See page 8D-6 in the 90 FSM.

Edited July 8, 2016 by padgett (see edit history)

[ChrisWhewell]

Still stumped on this.  Maybe a clue in the link below, the person had same problem, even changed cluster and BCM to no avail.  What is interesting is the expert John's reply, mentioning a ground he called "G103" underneath the alternator ??   I've seen a few threads about the grounds up behind the headlamps and at top of fender adjacent to the battery, but never saw anything about any "G103".   From what I can decipher from the OP's last post, is that a new ECM was the answer.    eek, maybe I'll try an ECM.... if I can find one ....

 

http://www.justanswer.com/car/130qt-90-reatta-shop-electrical-problem.html

Edited July 9, 2016 by ChrisWhewell (see edit history)