How to trace an intermittent short circuit in a car wiring harness
Intermittent shorts can happen while a car is just sitting parked, meaning they cannot be diagnosed by tracking down physical bumps or vibrations. Because replacing the sensor and connector often fails to fix the issue, the hidden fault remains trapped inside the harness, leaving owners struggling to narrow down its exact location.
What people tried
Every workaround mentioned in the threads below. We haven’t tested any of them — and nobody here is claiming they worked.
Found another way around this?
Share your steps and trade-offs so fellow engineers don't have to reinvent the wheel. No account required.
- 1Wiggling the wire harness manually to look for spikesDid this help you?
- 2Backprobing the signal wire at the PCM connector with a jumper wire to a meter while drivingDid this help you?
- 3Checking where the harness passes through the firewall for rubbed insulationDid this help you?
- 4isolating the load side from the supply side and checking continuity on each circuit individuallyDid this help you?
- 5testing continuity on every wire in the systemDid this help you?
- 6adding a 5A car fuse to protect the transformerDid this help you?
- 7Checking battery cables with loaded voltage drop testsDid this help you?
- 8Using factory diagrams to check ECM and TCM power and grounds while the vehicle is acting upDid this help you?
- 9Leaving the system off for a few hours until it temporarily resolves itselfDid this help you?
- 10Replacing suspected electrical components through trial and errorDid this help you?
In their words
Unedited, grouped by where they were said, most upvoted first within each place, each linked to the thread it came from.
“I have a intermittent short on a FTP sensor circuit (at least I believe) it comes and goes this is for a 06 mustang I’ll put it in run engine off and it’ll float between 0-50 pa on my code reader other times it’ll be 16000 Pa which is when it’s shorting I believe as google says that’s the max value (5v=16000 pa) I’ve changed the FTP sensor and the connector for it but I believe the issue to now be in the harness somewhere what would be a easy way to narrow this issue down?”source ↗
“I've been working at an independent shop for three years, and electrical diagnosis still gives me trouble.”source ↗
“Intermittently, the dash comes on but the starter doesn't turn, sometimes with a Service StabiliTrak message.”source ↗
“This time the ECM and TCM wouldn't communicate, even when I tried opening them individually.”source ↗
“That’s the weird thing the car can just be sitting on the driveway and sometimes it’ll spike or hold steady it does not even need to be hitting bumps lol”source ↗
“I installed a new transformer on my Lennox air handler and when my system came back on it ran for about an hour then my condenser started rattling still blowing cold air but then it blew the new transformer big time what is happening”source ↗
“Is this a continuity test every wire in the system situation or is there something specific I could be looking at?”source ↗
“This heat pump does this randomly. If you leave it off for a few hours, it'll work fine for days, weeks.”source ↗
“It seems to me that something is pulling down the 24v. You can see the status lights reset.”source ↗
“It never does it long enough to do much diagnosis. It does this almost exclusively on startup, but its done it while it was running.”source ↗
“Really, I'm at a loss. Pretty much everything electric has been replaced.”source ↗
“what we do when i attention to a court circuit in machine like this with mluti button what we do to separtion the probleme of court circuit to never get again in any country i want solutuion worked?”source ↗