Bitsyncmaster
05-18-2012, 06:44 AM
Relay grounds in our car seem to be more problem then I thought. I did find a bad relay ground in my car by accident since my solid state relays would still work with the bad ground. Most of the relay grounds are just for powering the relay coil to switch a circuit on or off but some do need to conduct some current for loads. The one that can cause problems is the dome light socket ground. Since the dome light unit will keep your dome lights on after the doors have closed, it conducts the current for the dome lights though that socket ground. If your running incandescent bulbs that current is about 1 amp in the ground wire. If your ground connection has 10 ohms of resistance then you're only going to provide 2 volts to the dome lights and probably burn out my dome unit since it uses that ground to power its circuitry.
The really grounds are wired in a daisy chain with the right most socket wired to the common ground. So depending where your bad ground connection is will cause problems for all the relay sockets to the left of the bad one. My fix was to make up a new ground buss on my car. So each relay socket has one wire crimped to the terminal and all those grounds get tied to one common splice and then one wire goes to the common ground.
So as a precaution, I recommend you pull your left most relay in the two relay banks and use an ohm meter to check the resistance between its ground pin and the common ground point.
I've also come up with a hardware/software change for newly produced dome units that shut down the unit if the ground voltage drop is excessive. This will prevent burning out the dome light unit.
The really grounds are wired in a daisy chain with the right most socket wired to the common ground. So depending where your bad ground connection is will cause problems for all the relay sockets to the left of the bad one. My fix was to make up a new ground buss on my car. So each relay socket has one wire crimped to the terminal and all those grounds get tied to one common splice and then one wire goes to the common ground.
So as a precaution, I recommend you pull your left most relay in the two relay banks and use an ohm meter to check the resistance between its ground pin and the common ground point.
I've also come up with a hardware/software change for newly produced dome units that shut down the unit if the ground voltage drop is excessive. This will prevent burning out the dome light unit.