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1985 Oddity Posted by Justin VanAbrahams [Email] (#32) [Profile/Gallery] (more from Justin VanAbrahams) on Thu, 5 Oct 2017 19:57:21 Members do not see ads below this line. - Help Keep This Site Online - Signup |
Ran into something weird today... while trying to button up the T5 conversion on my SPG, I started it up for the first time since May. It sprang to life and settled into a nice idle. I let it run for about 3 minutes and then turned it off. Well, I turned the key off. The car kept running. That was unexpected. I pulled the fuel pump fuse and it died.
Then I spent an hour going over all my Trionic wiring and found that with the key off there was still 5v coming across that ignition switch wire, keeping the ECM alive.
Long story (REALLY long story) short, I found there is no diode on the alternator light on my cluster, so the exciter gleefully back feeds the system with the key off. I guess with LH 5v was enough to shut down the ECM, but Trionic doesn't think 5v is off enough and keeps running.
All the wiring diagrams show a diode, and I yanked a 1990 cluster from the garage to verify it had one. I don't understand why my '85 doesn't have one, but I guess be warned all ya'll... if you try to T5 an '85, you may need to install a diode on the alternator light!
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