Back in 2000 I needed an RPM shift light for racing purposes
I purchased an AutoMeter model, They have several models that require additional purchases for RPM Pills.

It only comes with 1 RPM PILL, that was 3,000 RPMs.
This pill trips the shift light when engine RPM hits 3,000 RPMs

Of course that pill is useless, so you are forced to buy from that vendor a pill kit that is 5 modules,
so if wanting the 6,000 to 6,800 RPM range cost is another $75

So you need to swap the pill for the engine RPMs you want the shift light to come on

Now if for some reason you also want pills in the 5,000 RPM range you have to pay another $75 so now you're into it for $150 just for maybe a couple different RPM shift points

In my case did want to do some engine testing and needed that 5,000 range as only having the 6,000 RPM range
When I saw it would cost me another $75 it pissed me off and decided to backward engineer and with about $15 in parts and my time
designed a function, so no pill was needed and also now could slide a switch for a set point from 0 to 7,000 RPMs

That also means not having to keep 10 pills in car and have to manually swap when needed and that only can be done when car is off

Where my mod I can change that light trigger RPM even while driving

During a testrun I would slide switch to RPM I wanted the light to trigger on and captured that with a Scanner to see if I shifted at the RPM the light came on and would change shift point and results can see as I upp'ed the RPM set point and then did this from 4,000 to 6,500 range

I change the RPM trigger 8 times and each one I then shifted when shift light came on

Also showed that there really was no big torque gain if shifting at 5,000 RPMs to 6,500 RPMs

Click on each image to enlarge photo