build your own shift light, or get ripped off by ebay misadvertisement Options

[CilverSeliST205]

http://cgi.ebay.com/ebaymotors/SILVER-BLUE...609165518QQrdZ1

Above link sends you to a product called universal 3a racing shift light, which is not so universal since it needs a aftermarket 3a racing tach to work, but the seller "forgot" to mention it...

anyways, i ended up paying $25 for a aluminium tube with 4 led in it Can not return the product so i got to make it work.. here is how i want to do it:

OEM tach gets an input voltage corresponding to the rpms(please correct me if im wrong) if i run a variable resistor from that input to the base of a transistor that would switch 9V to the LEDs, then I will start the car and set the resistance to the low end and rev the car up i will get enough current to the base of the transistor to switch on the LEDs in shiftlight somewhere in low rpm range... then with increasing resistance i will get the LEDs to go on later in rpm range, and that is how i am going to adjust.

Am i going to make the tach read unaccuratley? Does tach input wire uses voltage as the only reference to rpms? Is this going to work at all? Thanks for reading/responses!

[creis]

^ he is right that shift light has a green wire also, however its listed to be adustable from 3k to 12k probably reads the rpm signal and goes to whatever settings its suppose to.

Side Note: whats the purpose of a shift light, seems like the only need for it is if someone is just learning to drive a stick shift? I mean its pretty easy to tell when to shift if your driving normaly, and it only takes a few launches to konw when to shift for the best acceleration.

[CilverSeliST205]

^ he is right that shift light has a green wire also, however its listed to be adustable from 3k to 12k probably reads the rpm signal and goes to whatever settings its suppose to.

Side Note: whats the purpose of a shift light, seems like the only need for it is if someone is just learning to drive a stick shift? I mean its pretty easy to tell when to shift if your driving normaly, and it only takes a few launches to konw when to shift for the best acceleration.

Yea back on topic my so called "shift light" has only 2 wires...

Side Note: shiftlights are nice when you have lots of power thats throwing your tach needle with the speed of light in first and second gear and your trying to get the max. precision with min. eyes on the tach.. I think it was talked about in this thread:
http://www.6gc.net/forums/index.php?showto...&hl=shift+light