Figure 9: Step 3c - Trace Each Control Circuit's Path ECM Applies Ground on BOTH Terminal 54 & 41 = High Speed Cooling Fan All 5 relays are now on and the fan runs on high speed. the starter relay's solenoid output was showing 0.1 ohms to ground. That might explain the no crank but what about the 25 amp fuse being fine? Something wasn't adding up. Avoiding Disasters by Learning from Others December 2016 Dave Hobbs When something doesn't add up - STOP! There is most likely a reason it doesn't add up. In my case, I didn't stop. Dad's timeless advice to me in the service bay was always this; "Quit for a while. Walk away. Work on something else. Get a cup of coffee." Well I never acquired the taste for coffee I guess. On the Sonic, I became impatient, assumed the schematic was wrong and totally forgot that a good starter solenoid indeed has about 0.1 to 0.3 ohms of resistance between ground and its switch terminal. What looked like a short that couldn't be (0.1 ohms would be 120 amps of potential current draw) would have turned into around 7 amps on that little yellow wire coming from the starter relay as the pull in winding switches over to the hold in winding. Had I have waited and thought it out I would have simply checked that starter "S" terminal's resistance to ground directly at the solenoid with the relay control wire disconnected. But I was working in Southwest Florida in July where it was 95 degrees in the shade and 100 % humid- Figure 10: B.E.C. (Bussed Electrical Center) after the fire! Relay had been removed in order to activate a circuit with power using a fused ammeter. A simple bit of confusion on which terminal went to the load and which was the relay's ground. 10 amp Fluke 87 meter fuse survived but the customer's B.E.C. was not as fortunate! ity. I was hot and miserable and just wanted to get this car diagnosed and repaired. So what did Mr. Impatient do next? I switched my supply of fused B+ (fused at 10 amps through my Fluke 87 ammeter jacks) to another terminal in the empty relay slot on the B.E.C. 7 MACS Service Reports