I put on some Hella 2020's last week and noticed that the fuel gauge starts to drop noticably when I turn them on. When I turn them off, the fuel reading slowly climbs back to it's proper level. I did put the switch and relays on one ground, but it's seperate from the other instr. cluster ground. The lights are great, but I'd like to get this bug worked out so it doesn't eat at my brain at night.

I'm a wiring nubie, but can usually follow paper intructions (when I read them).

 

Sounds like one of the wires you ran is causing interference with the resistance going to your gauge cluster. Reroute the power source wire for your lights, re hook up and try the lights again..

 

I ran the power source wire and light power wires through the little rubber boot of wires that goes through the firewall. I'll try to find another opening.
Thanks!

 

First, use a relay for the lights. The less power to go the distance the more power at the end. Your switch should be switching very low amprage. Just enough to trigger a relay (250-500ma. Thats .025-.05 of an amp) You can even tap off a fuse that goes on when the truck is running so you don't forget to turn them off and have a dead battery.

 

Agree on relay.


Best and safest to (wire like below):

• Use switched-ground control
• Take load power for the relay directly from battery through a fuse, not from wiring in the cabin. Fuse as close to battery plus as possible. Load wire between battery, fuse, relay and lights as short as possible.
• Take positive control voltage tapped from marker lights, and

This way:

• Relay is a close to battery and lights as possible,
• You will not forget to turn fog lights off (assuming you have light reminder feature),
• Only the grounding wire runs a long path from relay coil to cabin to your switch. Worst-case that that long wire shorts to ground, you just turn fog lights on.
• You stay consistent with Toyota's switched-ground control scheme.

To Clarify Physical Location of parts...

 

I didn't get a chance to mess with it this afternoon, but there are two relays (one for the driving lights and one for the fog lights) and an inline fuse in the system. I followed the Hella installation instructions on this adventure. Originally the the power source wire was tapped into the battery terminal and then I tried tapping into a fuse. Both of those options resulted in the fuel gauge drop. When I get the drop remedied, I'll definatly opt for tapping into a fuse.

 

Great info, rad4runner! I'll try to get on it tomorrow with your diagram and tips in hand.
Thanks!