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Electronics / A lesson in grounds
« on: June 05, 2014, 11:37:56 AM »
So I was dealing with some really odd electrical gremlins. Last night, I learned what can happen if you pull the dash out and PO515 the interior and dynomat over the transmission tunnel. You effectively block grounds that are connected to the metal bar underneath the dash.
Symptoms:
-No Vent control
-No Hot/Cold air control
-Intermittent blower fan
-Eventually lost dash lights, RPM guage and cigarette lighter
-No blown fuses
-No A/C Request (or light)
Nice thick coating of POR-15 over everything. Looks pretty, but man this screwed me. The metal dash support bar couldn't make good ground with the body of the car at the pillars and transmission tunnel. I also suspect the threading in the bolt holes were nicely coated with PO5-15, making the bolt itself not much help getting ground.
Adding to the problem, DynoMat covering the trans tunnel to make a nice thick barrier of "tar" at those 4 bolt connection.
The dash wiring harness has two ground points that goto the metal dash support bar. These are not even touched when you remove the dash, but the dash support bar still needs to ground to the car.
To troubleshoot what was going on I had to remove the dash wiring harness from the dash and put back in the car. Without it, you cannot test much. Maybe only the HVAC motors themselves, but you cant test for resistance through the circuit when you change temp controls from hot to cold for example.
This is the madness testing everything with all the harnesses, gauge cluster, and HVAC controls in place, but no dash.
Got really crazy electrical behaviors until I took those two ground pigtails and grounded them myself to a door bolt. Then EVERYTHING WORKED! I wire wheeled all the connection points to bare metal and I'm running another groundwire to that support bar. That-ought-do-it!
Careful with those grounds!
Symptoms:
-No Vent control
-No Hot/Cold air control
-Intermittent blower fan
-Eventually lost dash lights, RPM guage and cigarette lighter
-No blown fuses
-No A/C Request (or light)
Nice thick coating of POR-15 over everything. Looks pretty, but man this screwed me. The metal dash support bar couldn't make good ground with the body of the car at the pillars and transmission tunnel. I also suspect the threading in the bolt holes were nicely coated with PO5-15, making the bolt itself not much help getting ground.
Adding to the problem, DynoMat covering the trans tunnel to make a nice thick barrier of "tar" at those 4 bolt connection.
The dash wiring harness has two ground points that goto the metal dash support bar. These are not even touched when you remove the dash, but the dash support bar still needs to ground to the car.
To troubleshoot what was going on I had to remove the dash wiring harness from the dash and put back in the car. Without it, you cannot test much. Maybe only the HVAC motors themselves, but you cant test for resistance through the circuit when you change temp controls from hot to cold for example.
This is the madness testing everything with all the harnesses, gauge cluster, and HVAC controls in place, but no dash.
Got really crazy electrical behaviors until I took those two ground pigtails and grounded them myself to a door bolt. Then EVERYTHING WORKED! I wire wheeled all the connection points to bare metal and I'm running another groundwire to that support bar. That-ought-do-it!
Careful with those grounds!