upshift light bulb

dw1 · 06-10-2021, 01:51 PM

There are some good threads on gage repair, particularly the one by "Determined" on his tach fixes, but none of them cover the upshift bulb specifics.

Can anyone tell me anything about the upshift light bulb (for example, voltage and wattage)? This a PCB-mounted incandescent bulb mounted in the tach.

Because I was taking the tach apart to clean the glass, I did some diagnostics and found the upshift bulb (known as CASIS) was dead. I know many find this light irritating, but I like that it also comes on at/near readline at full throttle and I'm also trying to get my car working as original as possible. BTW, this is from an '87 3.2.

Joe Bob · Joe Bob's Garage

Looks to be similar to the gauge light bulbs. I consider it a worthless nanny light. You are better off w/o it...%^)

pavegeno · pavegeno's Garage

Mine works perfectly on my 88 and I like it. If you replace the bulb and it doesn't work, the DME module under the seat (not the DME relay) controls the light. Mine recently failed and I sent the DME module back under warranty and got a new (old) one and CASIS works right. It serves two purposes. As you noted, it will come on at/near redline to remind you to upshift. Second, the light will come on under soft or medium acceleration for fuel efficiency. Pretty cool system. Like you, I like every detail, no matter how small, to work.

mo-mon · mo-mon's Garage

I agree with Joe Bob. Mine works & I pay no attention to it. The day the bulb goes, I won't replace it.

HaroldMHedge · HaroldMHedge's Garage

I consder the light as the lug me (engine) light.

It's one of these dash blubs.
900-631-102-90 12V - 2 watts
900-631-103-90 12V - 4 watts

Having it work is a personal option.

Edit
Taken from 89 PET.

dw1 · 06:52 PM

I understand that some feel that this indicator is nothing but an irritant, but I want mine working.

Sorry HaroldMHedge, but this is a standard-type T1 (3mm) incandescent bulb, far smaller than the dash illumination Ba7's. The bulbs you list are the dash illumination bulb and the license plate bulb. This upshift light bulb is not one of the bulbs that plug into the back of the tach - it is soldiered to the tachometer PCBA.

Irritatingly, this lamp & base assembly is quite non-standard in that it has no markings.

T1 incandescent bulbs come in a variety of voltages from 2.5V to 28V, with 5V, 12V, and 28V being the most common. I was just wondering if some of the knowledgeable people here who have dissected and fixed their tachs (like member "Determined") might have some knowledge of the CASIS lamp voltage & wattage.

It would be a major PITA to do trial & error, especially since disassembly of the tach & soldering in the replacement is required for this bulb, and I'm trying to avoid that more than once.

gamin · 06-11-2021, 04:00 AM

In my 88, I didn't find the light to be useful so I installed a voltmeter in that space. Now I have important information displayed.

famoroso · 06-11-2021, 07:05 AM

Quote:

Originally Posted by HaroldMHedge

I consder the light as the lug me (engine) light.

I agree! In fact, I wouldn't be surprised if some of the valve guide wear issues in the 3.2s weren't exacerbated by people following that "idiot" light's finger wagging "recommendations" and lugging their motors / driving them incorrectly leading to higher than normal cylinder head temps.

If I recall correctly, you can pull one of the wires from the rear of the tach and it disables the fuel economy portion of the system while retaining the upshift at redline functionality. Honestly tho, that little light, buried at the bottom of the tach, is hardly an efficacious shift light. That being said, I appreciate that there are those that want to have everything work as designed.

Larmo63 · 06-11-2021, 08:01 AM

One of the first things I noticed when I went to look at and test drive my '86 Carrera was that little arrow light. I had never owned a Porsche new enough to have high tech stuff on it like that. I pay no attention to it now, as I don't seem to be someone who minds his 'nanny' very well. If it stops working, it won't hurt my feelings.

By the way, Frank said "efficacious."

Nice word.

GH85Carrera · GH85Carrera's Garage

Quote:

Originally Posted by gamin

In my 88, I didn't find the light to be useful so I installed a voltmeter in that space. Now I have important information displayed.

This.

100% original is nice for Concours cars. Mine is a driver, so I have modified and vastly improved AC and the silly shift light was replaced with useful information.

I also replaced the dumb temp gauge with one with real numbers. I don't care if it is not as sold. It can be put back easily enough.

As far as finding that bulb, I have no clue. I bet somewhere on the site there is a thread about it.

Good luck.

dw1 · 06-11-2021, 03:56 PM

A specific technical question was asked, acknowledging the previously-posted opinions, so I hoped for the best. But alas, the replies were a rehash of previously posted opinions about the value of this feature and a bit of misinformation. Oh well...

Seriously, I saw the tech + voltmeter in a previous thread and gave that careful consideration, but instead decided to use a cigarette-lighter plug-in voltmeter for when I was concerned about the alternator and/or battery.

As far as the CASIS bulb itself: I decided to solder some test leads to the tachometer PCBA, partially reassembly the tach and install it in the car so I could test it. To no great surprise testing showed the bulb is a 12 - 14V one, and dimensional measurements make it a 3mm (T1) bi-pin package with 0.100 inch lead spacing. There isn't a whole lot of choice available these days in T1 incandescent bulbs, so I ordered some typical 12 V, 65 ma, 0.15 MSCP units and will see how that works out.