Making a variable pill for AutoMeter's 5340 Shift Light.

I bought an AutoMeter shift light and some RPM pills for it. The price kinda floored me: $25 for 5 pills that covered a 1000 rpm range.

That meant that if I wanted to vary my shift lite indicator from 4800 to 6200, I'd have to spend $75 in pills...and the light comes with a very useful 3000 rpm pill to start with. By the way, the light costs about $63. So the cost of the pills would have been more than the light itself. Sounds like effective marketing techinques to me.

So I installed the light to verify that it worked.

And boy, did it EVER! That puppy is bright! Luckily it comes with a translucent cover that helps tone it down a little.


I mentioned this dilemma on the Nova mailing list and Alex Bilan suggested that the pills might just be simple resistors. He was absolutely right. The image on the left shows the resistance readings in ohms. The first 4 readings are measured readings and the rest are extrapolated.

Then I ran a chart to see if there was a linear relationship. The image on the right shows a VERY linear relationship between resistance and RPM.

So I made a quick trip to the local Radio Shack store and brought home the following items:
Molex connector, part number 2740222, price $0.99
5k Ohm Linear potentiometer, part number 2711714, price $1.49
Knobs, package of 2, part number 2740403, price, $0.99
Total (including tax) $3.69 US

Then I trimmed the Molex connector so that the male connectors protruded thru, just like the connectors on the pills.

I had to do a little adjusting to get the tangs on the potentiometer to line up with the pins in the connector, but not bad. Here the whole assembly is being held in place by a craft from another solar system...or is it a pin removal tool? I forget.

Then I soldered the connectors together. This is the semi-finished product.

I plugged it into the slot for the pill and this is the result. The shaft on the pot still has to be trimmed and an enclosure built.

And here it is lit up like a...well...shift light (with the cover in place.) I've tested it up to 5000 rpm...and it seems to work fine. Not bad for an afternoon's work and $3.69.

I made another trip to Radio shack and bought a small plastic project box. It was about a dollar. Then I cut it in half and drilled a hole for the shaft of the pot and for the alignment tab. Then I trimmed the shaft and installed the knob.

I also created a little graphic to give a rough estimate of where the adjustment was. That tape is gonna have to be trimmed and the edge of the box could use some smoothing.

Then I cut an opening in the top of the box so that it could fit the light housing. almost looks like it belongs there. And $5 is a lot better than $75.

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