A GP test TOOL to pinpoint heat at wired tip of gp while in car.Key activating gp circuit ,should be some heat to get a reading.Its another way to get results if it works .https://www.youtube.com/watch?v=LONm564Hv_k

I tried that several years ago but wasn't sitting in the car rather standing beside the engine. Unable to detect any difference.

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92 e300d2.5t
01 e320
05 cdi
85 chev c10

If you glowed maybe 5 times it might show a temp change for it to be a gauge?It wouldnt have to show much difference ,just enough to allow a look of a working and non working gp.Ive seen a thermal imaging test tool pickup thermal on this same gp run of diagnostic, these are soooo much cheaper.

You can use that to find a misfiring cylinder, or to locate which side is out on a V-8 Powerstroke when a valve cover harness connector fails.

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Brian
87 300Dturbo 180K #14 head still running R-12 SOLD 12/2017
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05 Chevy Express 1 ton w/Royal Utility box 120K
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