Tach is dark, until highbeams are turned on

[b0rderman]

Early 911 newbie here. I am trying to get my tach to light up at night, like all my other gauges currently do. I thought (and hoped) I had a bad bulb so I replaced it. No luck…but I finally ran into another aircooled car on a recent night drive and I flashed him hello from the other side of the intersection…sure enough, my tach light flashed itself on at the same time. Woohoo!

Can anyone point me in the right direction to try to correct this problem? High beams on, tach illuminated. Highbeams off, tach dark. All other gauges glow so nicely.

Unfortunately, I am also an electrical newbie, but that is changing by the day.

And just in case I minced words above, my issue is not with the well-documented high beam indicator light, but the light that illuminates my tachometer at night.

Thanks for any ideas on where to look first.

Edit: 1970 911e

[PorterF]

Does the high beam indicator light come on with the other instrument lights? It sounds like two of the instrument lights are switched.

If this was a later gauge I would try switching the top two leads/bulbs. Probably similar to the early gauge too.

[gptom]

start with the ground wire on the gauge

[troutmaskreplca]

Seconding ground wire. Remove, wipe clean, re-seat.

[timmy2]

What are the wire colors going to the tach gauge illumination lamp?
Is it still daisy chained to the other gauges with black/blue wire?
Or has it been spliced into the hi beam indicator light?
The gauge lamp harness was flimsy at best when originally made.
Worse after 50 years…

[GH85Carrera]

The instruments wiring is sketchy at best, even when the car was new. The lighting circuit has NO FUSE in factory original form. Be sure it has a fuse "while you are in there" and clean and check every ground.

We all like to think of our cars and the pinnacle of German engineering. The engine and most of the car is, but the electrical parts are often rather poor. It is a long story, but the 911 was destined for the scrap heap and was going to be replaced by the 928 back in the late 1970s. Only when the American, Peter Schutz took over as manager did the 911 get a reprieve, and the company was on the verge of bankruptcy.

[b0rderman]

I appreciate the suggestions. I popped the tach out, and just took some time to clean all the contacts, and re-attach everything firmly. Now, the high beams flash only when the headlights are off, and do not flash when the lights are on. The tach still only lights up when the high beams flash.

A step backwards...

On a mostly positive note, my turn signal arrows kind of light up correctly now. Before only the right turn signal indicator arrow would work, and only for three flashes. Now, at least ~70% of the time, both turn signal indicator arrows work correctly. However, sometimes the left turn signal causes both arrows to flash on that tach. The actual turn signals on the corners of the car continue to work as they should.

One 70% step forward!

None of this was intentional, monkey with a typewriter...but I'll keep monkeying around with the tach wiring from time to time and let you all know what happens next. I'll also spend some time getting to know the diagram a bit better, to and from the signal/high beam stalk.

[HarryD]

Add a location to your profile. A Pelican may be nearby to help you.

I suspect there are some wires in your car that are not correctly landed. If you do not have one already, you need a full color wiring diagram for your car. From an earlier post, you appear to have a 1970. Timmy2, posted this link for the wiring diagram: https://www.dropbox.com/s/32266dstkfqnwrx/SL35-Master.pdf?dl=0

[Bill Douglas]

There is a knob I turn. I can't remember which - maybe the light switch itself. And it turns the brightness of all the gauges up and down. Does this work and does it effect the brightness of the tach? tested with high beams and low beams.