Leaderboard

New ICM has the exact same resistance as the old ICM from pin B (bypass circuit) to the case ground of 9.6 ohms. So I put the old ICM back in and did the ground short test again, this time using a test light as the manual says to do, instead of a voltmeter, probing ECM harness BC7 and the other end to 12V. The test light did not come on. Voltmeter still showed voltage of 11.4V. I feel somewhat led astray by the service manual because in the intro to the electrical section it says a voltmeter can be used anywhere a test light is called for. Apparently that is NOT the case, because even though the voltmeter read 11V, there was not enough of a ground to light up a test light. So maybe a resistance of 9ohms to ground does not indicate a short. I did use the Deoxit D5 on the ECM connections. I also found the battery cable's negative terminal stripped, so I replaced that. Drove the car for 8 miles without any problems. I don't know if I fixed it or not. I guess time will tell. 🤷 I'm afraid to return the ICM before I know for sure, because that could invoke Murphy's Law 😳 in addition to Ohm's

I'm not an electronics expert, but most likely the ICM uses SCRs to trigger the coils to fire. The SCRs may leak some voltage, which isn't unusual, but still not allow enough amperage through to turn on a test light. Maybe that is the reason they recommend using a test light. My comments are based on the ignition system on Evinrude boat motors I've owned that use SCRs in their electronic ignition systems.

I don't think you are going to find a wire in the IPC connector that comes from the photocell. The wire from the photocell goes to the BCM. The BCM controls the brightness of the IPC and CRT based on inputs it gets from the photocell and the dimmer slider on the headlight switch. You haven't mentioned the CRT. If the CRT is working properly the photocell isn't likely to be your problem.