Car runs great, gauges function perfectly until...

- When I use turn signals, both temp and voltage gauges "bounce" in tandem with the signals.

- When depressing the brake pedal, temp gauge goes full right (hot), voltage drops to 9

- When I turn on the headlights, temp buries full right, voltage buries full left

Suggestions??? Thanks guys....

https://colorwiringdiagrams.com/products/po...-fuel-injection is money well spent. It's large, in color, and laminated. Sounds like you should check all of the grounds and make sure they are clean imho.
Chris

Where to start?

Given the limited information, you only mention anomolies with the center console gauges. Is that it? (Of course, I am assuming a center console, not an aftermarket triple gauge cluster.)

Is this a new issue, or something you've had/observed since owning the vehicle?

Next assumption/question...was the console/cluster factory or was it installed "after-the-fact" by a previous owner.

There are definitely joys to owning/driving a 914...one of them is NOT having a car where the OEM wiring harness has been "butchered" by umpteen previous owners.

If you don't already have a copy for your vehicle (what year?), locate a good, colored, wiring diagram (obviously with a legend).

As a start, I would recommend disconnecting the battery and pulling the two screws for the fuse panel under the dash...do the wires on the back side of the fuse panel look as they appear on the wiring diagram or have they been tampered? This should be a good indicator of whether this is a simple diagnostic exercise or if the issue may be related to another wiring/installation issue.

A good multimeter should be a part of everyone's toolkit.

The 914 is notorious for ground issues. Although, just saying that isn't very helpful...this is where the multimeter pays dividends...one circuit at a time.

I don't want to sound negative...the more info you can provide, the easy it will be to diagnose the root cause.

Ground issue for sure ,just had this with my VW Corrado,tacho would read fine then with headlights etc on the rpm would read lower, pulled the fuse box and the earth was cut for the gauge cluster when it had a crappy alarm fitted,no differant with a 914 with the exception that the wiring is some what older .
Make sure you have a good clean earth clamp on your battery also.
Find all your earth posts and clean them up as well as the wiring eyelets be really fussy with these points ,I cleaned up the post threads and used new bolts and washers,one of the first things I did before starting mind numbing wiring changes for 911 gauges.
Good luck you will get there.

Agree. And load up a small wire wheel on cordless drill to do the ground connection cleaning.

Thanks guys. It's occurred to me that this all started after I had the battery out/ground disconnected for the Winter. Will follow your suggestions tomorrow and report back. Thanks!!

add one for suspecting dodgy grounds. I'd start by checking / tracing through the gauge GND wire...

- Tony