Updated: USDM Foglight harness mod - Honda Prelude Forum

axion68 · 03-06-2003, 11:31 PM

Tonight I sat down and figured exactly what the 4 wires that go to the black relay did. I am positive I have it right this time, so here you guys go (I even tested them for a while and had no problems).

Tools:
Small Flathead Screwdriver
Electrical Tape
Solder iron and solder (or some sort of crimp on connector)
Terminal ring
Wire (lenth will vary, but atleast 4")

1. Remove the foglight switch holder as you did when installing the holder the first time. To do this wrap a flat head screwdriver in a towel and gently pry the housing out. There are 4 clips holding it in. You will be able to see them when it starts coming out.

2. Find the 4 pin black relay, and disconnect the plug. Now remove the little white housing from the brown connector, this will expose the wires.

3. Remove the black electrical tap and as much wire loom as you wish, you want enough room to be able to work with the wires. Now cut the blue wires with the red strips (give yourself more wire than I did).

4. Now you want to connect the headlight ground wires together (they are in the red box below). Then grab some spare wire (long enough to ground to a bolt somewhere), put a terminal ring on the end of it, and connect it to the new relay ground wire (yellow box in picture below).

5. Put the white cover back on the brown connector (or electrical tape the connector up if you can't get it back on) and plug the connector into the relay. Bolt both relays as well as the new grounding wire you made up. Clean up anything else and make sure the fogs work (parking lights need to be on). If so put the switch holder back and have a beer.

red92si · 03-06-2003, 11:44 PM

nice... great info

Niffum · 03-07-2003, 01:10 PM

Thanks for letting us know the updates!

99LudeSpeed · 03-07-2003, 02:46 PM

thnx for the update

pIOUs · 03-07-2003, 05:30 PM

Well done. Always nice to see a clean and simple solution. Keeping the relay is exactly what you want to do.

alphajesse · 03-21-2003, 02:48 PM

does this setup keep the fogs on with the highbeams, or do they still turn off in that case?

axion68 · 03-22-2003, 10:38 AM

fogs turn off with your highbeams. if you ran a test light on the gold relay I'm sure you could figure out a way to bypass the high beam cut, but it isn't a big deal (for foglight users).

shukuchi_2003 · 05-19-2003, 10:51 PM

Is this the solution to being able to turn on the fogs WITHOUT having to turn on the headlights first? That means being able to turn on the fogs with the headlights off.

axion68 · 05-20-2003, 01:17 AM

Quote:

Originally posted by shukuchi_2003
Is this the solution to being able to turn on the fogs WITHOUT having to turn on the headlights first? That means being able to turn on the fogs with the headlights off.

you have to have your parking lights on (IE tail lights/guages/side makers) but you don't have to have your headlights on. The USDM relays require your headlights to be on. With this mod you have the option to turn your headlights on too, but you don't have to have them on. You just have to have your parking lights on.

gioe · 05-20-2003, 03:35 AM

I don't recall my foggies turning off when my high beams are on. Then again I have a JDM harness...would that matter?

Perhaps, I should double check that. I could be wrong.

This should be FAQed.

Greek Lude · 05-20-2003, 11:53 AM

I have a JDM harness with USDM switches. I got them setup to be indipendant of the headlight beams regardless if there on or off.

axion68 · 05-21-2003, 11:14 AM

Quote:

Originally posted by gioe
I don't recall my foggies turning off when my high beams are on. Then again I have a JDM harness...would that matter? Perhaps, I should double check that. I could be wrong.

This should be FAQed.

The JDM harness allows your driving lights to be on whenever you want. Yours should turn on whenever the switch is turned on, regardless of if your headlights/parking lights are on. The USDM harness was designed for fog lights, and there are probably regulations in the US that requires your headlights to be on or something.

dat.silver.lude · 05-21-2003, 12:01 PM

Quote:

Originally posted by JakeTheSlayer

and there are probably regulations in the US that requires your headlights to be on or something.

Yes, there are...

Tony · 05-21-2003, 01:01 PM

Quote:

Originally posted by dat.silver.lude

Yes, there are...

how so when numerous vehicles come from the factory like this even american cars such as the Cadillac CTS.

axion68 · 05-22-2003, 01:28 AM

Quote:

Originally posted by Tony

how so when numerous vehicles come from the factory like this even american cars such as the Cadillac CTS.

well, I know in Idaho (and I assume anywhere else in the US) you can only have 2 sets of lights on. Your high beams and low beams each count since they are both on. That is why your fogs cut out when you turn your high beams on. I'm sure there are other regulations on how you have to have your headlights on for your fogs to be on or something like that.

Tony · 05-22-2003, 06:21 AM

i know about the 2 lights law, but i was referring to the fogs only comment.

pIOUs · 05-22-2003, 01:10 PM

Quote:

Originally posted by Tony
i know about the 2 lights law, but i was referring to the fogs only comment.

The question was answered. JDM harness can allow up to 6 lights on at a time if triggered by the parking lights.

The USDM harness complies with US laws by making it functionally impossible to have more than 4 lights on at a time by tapping into the headlight function and turning off the fogs when the brights are on. Aside from cutting the lowbeams when the brights are on, there is no other way to comply. Other vehicles do this, but our headlights are designed so that the highbeam extends the low beam function and isn't a standalone feature.

The 2nd gen eclipse is identicle in function and must be rewired to function as the Prelude JDM wire harness does BTW.

Further, If the factory harness was not tied into anything on the steering column (ie: you just push the button to turn on), you would be illegal once you had fogs on and activated the brights. That's the theory anyways. In practice, it is really not obvious that there are 2 bulbs on per headlight when the brights are on. Since they are integrated, the cops won't zero in on that one compared to driving with 6 sets of fogs activated like some of the morons out here do.