I do a little fly fishing when I have an opportunity. Some anglers consider the Elk River one of the best trout streams in the Eastern U.S. It has native Brook trout, and plenty of wild Brown and also Rainbow trout. It is 248 miles from my house. You take 77 south and catch 79 out of Hillsdale. I wasn't going quite that far. A friend of mine has a trucking company near Big Chimney.

He said that "They threw everything at one of his trucks including the kitchen sink. This truck had issues with the dash, the gauges would go dead at times and had the following codes:

SID 251, FMI 4; SID 231, FMI 9; SID 231, FMI 13; SPN 639, FMI 9; SPN 639, FMI 13.

"The ECM was replaced, as was the VECU," Larry, the owner said. His technician, Dale Richmond, was also there.

"Is the VECU new or is it a reman box?" I asked.

"Brand-spanking new," Larry replied.

"Anything else?"

"I installed both terminators. There's no communication with the brake ECU, SRS ECU and the VECU. Oh--and I fixed a broken ground near the starter."

I wrote it all down. "Is that it?"

"I found 160-Ohms on the ground for the ABS/ECU, cleaned it up and used Stabilant-22."

I noticed that the multiplex DTC's would go inactive every 45 seconds and then went active for 5 seconds--strange.

"One of the guys said the pitch of the twist in the wiring could be wrong. Or that we should change the terminating resistance."

"Don't do that. Keep the terminators as is."

"Why?" Dale asked, "Why do they put the terminators where they do and why keep the value the same?"

"Because of Electromagnetic Compatibility," I said.

Dale turned to Larry. "In other words, boss, he doesn't know."

"Firstly," I said, examining the fuse box, "Both terminating impedances have to be balanced between the two wires' terminating ends and matched to the characteristic impedance so as to minimize signal scatter when high baud rates are used. Secondly, both wires must individually present the same impedance with respect to a signal ground and also to a shielding ground. Thirdly, both cables must have the same exposure to the interfering intrusion."

I looked at Dale. "Need I go on, my friend?"

"Nope."

"On this truck, the VECU controls the multiplexing. Can I assume that you checked the fuses and the wiring?"

"Yeah," Dale said.

  I checked the fuses and F81 had no power. Dale couldn't believe it. "Well, it had power when I checked it."

He grabbed the test light. It lit, indicating continuity across the fuse. "See? You must have had a bad connection or something."

I checked it again with the same test light. It did not light. Dale grabbed it and checked it again. It illuminated. He laughed, handing me the light. "I guess you Ohio boys talk up a storm with that technical garbage but you can't do the hands-on, eh?"

I started pulling the fuse panel.

"What are you doing now?" Dale asked.

"Look how the gauges are fluctuating," I said, "There's something going on with F81."

Sure enough, on the backside of the fuse box was a fleet tracking device. "This could be a problem," I said.

"The guy that installed it knows a lot more than you do," Dale said. I didn't know what his problem was, but I started to remove the case. "You know, I do electronics," Dale said. Alphonso and I designed that FTR and he knows more than anybody.

"Then why don't you call him?" I asked.

"He went out of business," Larry said.

I examined the circuit board. "We used a solid state relay and latching relay combination in parallel driven by different pins, as you can see. The SSR is powered up just long enough to switch the mechanical relay and then we switch the SSR off."

Wow--Dale impressed me.

"So, do you see anything unusual, professor?" He said that mockingly.

"Are you using an AC load in the circuit, Dale?"

He chuckled. "Of course not--you should know better than that, professor."

"Well, ace, the solid state relay you guys used is meant to switch AC loads only."

Dale's eyes widened. He looked at the SSR. "This relay won't shut off until the zero crossing occurs. Because you are using it on a DC load, then it stays on once switched on and will not turn off until the current goes to zero. It's putting just enough current into Relay RLY04 upstream to cause distortion."

I de-soldered the PCB SSR and scavenged one from Larry's scrap parts box, found inside a PDC box. I soldered it in place, checked the circuit. The dash functioned normally, the DTC's were gone and now I could test fuse F81 as well as Dale could.

Larry was thrilled. "Son-of-a-gun--let's go to dinner. It's on Dale," Larry said.

"Want to work full-time for me, Bob?"

"Nope--I'm 65 years old, I do this because I like it and if I do it for a living I'll hate it."

"Well, then, come on down and we'll do some serious fly fishing."

"Yeah--and we could do some canoeing," Dale said. Right when he said that, I thought about the movie "Deliverance."

"I'll pass on the canoe trip."

Oddly enough, the radio station I was listening to on the way home played the Dueling Banjos song. Creepy.