wire foglights as drl , act as normal

Hi

Right now I have a set of lights set up as my Daytime running lights that are on a relay that are wired into my parking lights, so when I turn my headlights on, the DRL turn off. I am wondering, could I splice my power wire that runs to the lights from the relay (87a) into the existing headlight (foglights) harness. My thinking is that when my headlights are on, I can then turn the fog lights back on using the factory switch. My relay is set up as follows:
30: 12v power supply
85: ground
86: switch from parking light
87a: output to foglights.
I want to just try it, but wondering how the power running through the system will react when i send power to the foglights with a relay on the system, ie: will power power coming from the 87a side blow the relay?. Any help would be appreciated, thanks.

It depends how accessible said relay that controls the daytime running lights is. If it is easily accessible, I would say go ahead and try what you've planned. As long as the output to foglights splices directly into the factory foglight relay you shouldn't have any problem with current handling, since it would be a low current draw.

You may have to add an isolating diode into the fog lamp circuitry to prevent current from passing through the factory switch in the reverse direction. This depends on how that switch is wired. Testing with a DMM should allow you to figure that out.

Some vehicles (like mine) have a relay embedded somewhere in them so that the fog lamps can ONLY come on if the low beams are on and the high beams are off (or something similar). You'll have to bypass that relay to accomplish this.

Finally, I would switch the 30 and 87a terminals. Reason for that is that if you supply +12V to the common terminal (30) then the N/O terminal (87) is live while the relay coil is energized. Having a live post sitting around leaves the possibility for a short whereas if the +12V goes to 87a then 87 will just be grounded and that's not really a problem.

Best of luck!

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1998 Ford Contour SE
Kenwood Excelon KDC-X794
Boston Acoustics ProSeries 6.2, Proton 250
Kenwood KFC-C6893PS, Proton 222

Thanks for the reply. I have since decided not to bother and got some other DRL led lights. Plus my car also has the fogs off with high beams, so i'm sure it would be more work in the end. I took your advice and switched 87a and 30. Thanks again.