Bizarre Datalogging Issue. TunerProRT/Moates Cable

[jmgtp]

Datalogging my car using TunerProRT. I use a Moates ALDL to serial cable, through a serial to usb adapter into the laptop - all works well with datalogging. That is, until I turn the headlights on.

Headlights on causes TunerPro to have data errors at a rate of about once per second. Headlights off, no errors whatsoever. If I turn the headlights on, and then turn the dimmer switch OFF (no dash lights) TunerPro works just fine. So the issue is, that if I turn the headlights on I have to turn the dimmer switch to off or I can't datalog.

What can possibly be causing this?
The only thing I can think of is that the Moates cable plugs into the 12v lighter socket for power and somehow the voltage might be going down on it just a smudge when the headlights/dash lights are on. Hard to believe, but no other idea. Voltage gauge reads 14v with headlights on. And I'd think that when I hit the brakes that is more of an electrical draw than the dash lights.

Not a huge issue for me since it not really a problem to just kill the dimmer switch. I can't see the gauges but at least the HUD stays on.

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[Joseph Upson]

The voltage change is probably exactly what you're dealing with. I've been having problems with my inverter supply to my laptop plugged into the lighter socket shutting off when idle dips low briefly. It's a safety mechanism built in to prevent draining the battery but I've noticed it is sensitive to it. With that being said you've explained the reason I was having intermittent problems with errors occuring during aldl connection as my backup laptop requires the use of the adaptor because of a weak battery and an accidental grounding had previously damaged the OE ground wire to the lighter socket. A thinner gauge ground wire has been connected to it making it more sensitive to fluctuations so I bet voltage fluctuation is what's causing the problem you are experiencing.

[Superdave]

I'd re-ground the cig lighter socket and see if that helps.

If you continue to have issues and are comfortable with modifying electronics then let me know...