Headlight relay mod revisited...my way to do it and save some money - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Tx Firefighter · 02-06-2006, 07:36 AM

I was wandering around looking under the hood of junk cars, scavenging hose clamps and other usefull trinkets when I spotted the perfect thing.

On a FWD Mopar puke car, late 80's, early 90's there is a perfect little bracket with two Bosch style relays on the fenderwell.

These are the exact relays you need to do the headlight relay mod and not have to order them or buy them new. A Bosch relay is a Bosch relay. These were priced perfectly, free.

Here's some pics of what I'm talking about...

If you do this mod, please do it right, so it's reliable.

I posted a picture of good quality crimping tools. Those 4 dollar do-it-all electrical tools suck. Spend 25 bucks and enjoy the good life.

I also posted a picture of a neat tool I use. It's a miniature butane torch. I originally saw the Boyd's guys using them on TV. My wife picked one up for me at Home Depot. It's a godsend for heat shrink tubing in tight areas.

Finally, there is a picture of a finished connection. Notice there are no connectors with colored plastic sleeves. Remove the sleeve and expose the bare connector. Then crimp with a good tool. Next, solder the connection to the terminal. Finally, cover with heatshrink.

Matt covered the basics of this mod in his post, I'm just elaborating on a good way to do it even cheaper.

70c10 · 02-06-2006, 10:59 AM

Nice write up!. How did you know which terminals to hook up the headlight wires???. They look slick.

Tx Firefighter · 02-06-2006, 11:08 AM

Go here, and look at page 5. I just printed the page off for my tech notebook that I keep on my workbench.

http://sonolithics.com/files/bosch.pdf

Warning, not for the dial up guys, that's a big PDF file.

Tx Firefighter · 02-06-2006, 11:57 AM

The sonolithics lists the terminal numbers on the relays, and if you look closely at the bottom of the relay themselves, the same numbers are on them.

Also, I swapped the driver's side headlight plug for a spare passenger side plug I had laying around. Once you cut the original wiring apart, you will be left with two extra unused wires on the left headlight plug. The right headlight plug is exactly the same, but doesn't have the two unused wires hanging off of it. I did this strictly for a neater appearance. I didn't want two little short stubs of cut off wires sticking out and looking shoddy.

shifty · 02-06-2006, 12:25 PM

Great stuff. Might want to include a link back to the original wiring explanation thread just for the purpose of archival. Curious - what car exactly did it come out of? (rough estimate?)
i went to the junkyard today and just wanted to let everyone know - you can find the relay setup that Tex is talking about on 92-94 Dodge/Plymouth's : Sundance/Duster/Shadow models and I think also on the Summit as well. The relay setup is bolted to the driver's side shock/strut tower with what looked like a 1/2" or 13mm bolt. I seriously found at least 10 of them in good shape - and I didn't even make it all the way through the Mopar section of my local Pull-A-Part, so they are definitely out there to be had."

Tx Firefighter · 02-06-2006, 12:42 PM

Late 80's or early 90's FWD Mopar with 2.2 or 2.5 engine. I think it was a Sundance or similar.

jhow66 · 02-06-2006, 12:47 PM

Here's how I set up my son's Blazer (orangeuavol).

69TowRig · 02-06-2006, 05:27 PM

Quote:

Originally Posted by 67chevemall

Man I have been lookn for a pair of those crimpers for toooo long now.

Home Depot has started carrying more "REAL" electrical tools. I know they have those there.

Personally I use a GreenLee ratcheting cyclical crimper. I have the dies for insulated and uninsulated terminals. Works like a champ and you don't get a hand cramp from using them.

Also, I have noticed that LMC is now selling a supposedly "plug-in" upgraded headlight relay harness. I believe it was $29.99

Tx Firefighter · 02-06-2006, 05:54 PM

Mine are Klein brand. They cost 22 dollars a few years back. Worth every cent too.

You can get them online for 20 bucks.

http://www.mytoolstore.com/klein/1005.html

72MARIO · 02-06-2006, 06:52 PM

I have a hard time understanding how this works. Page 5 is what I should be looking at for the directions ? Any specfic info on how to do this to our trucks ?

Russell · 02-06-2006, 06:56 PM

Oh, and here is how I did mine up:

http://www.zieglerdigital.ca/public/...tricfans01.jpg

I haven't run the power wire from the firewall distribution block to the core support dist block yet, but other than that, its all ready to go.

Still plan to buy an H4 European style bosch headlight conversion kit for the truck yet, both sealed beams have one of their beams burnt out.

I have an H4 kit in my 77, without the relays, and dang is it ever nice! Can't wait to see it done up with the relays!

jhow66 · 02-06-2006, 07:19 PM

Quote:

Originally Posted by Tx Firefighter

jhow66, where can I get one of those inline circuit breakers at? Anything OEM that I can get at the junkyard?

Got mine at NAPA. Got the ticket somewhere--will look up the number for you.

roger0080 · 02-06-2006, 07:29 PM

TxFirefighter, did these have any female plastic connector housings attached to the relays from the MOPAR donor car or did they attach like you show in the photo?

Tx Firefighter · 02-06-2006, 08:28 PM

72Mario. Basically, here's the deal. Power must travel from your battery all the way to the light switch then back to the lights. This induces a lot of resistance and voltage drop. The end result is that far less than battery voltage reaches the lights, causing them to not be as bright as they could be.

The relay mod changes all this. It makes it to where the power only has to go from the battery through the relay on the core support and then to the headlights. This is a much shorter pathway with fewer sources of resistance. The end result is full battery power reaches the headlight and that gives 30 to 50 percent improvement in headlight output.

Mad electrical has a great article on their website which explains this fully, in easy to understand language.

Tx Firefighter · 02-06-2006, 08:34 PM

Here is the link to MAD's article. There are two pages with lots of pictures.

http://www.madelectrical.com/electri...adlights.shtml

Roger, the Mopar used a nice plug with the wires securely positioned. Only thing was, the owner had stripped this car of it's entire wiring harness. So, I was able to get the relays, but not the connectors. I'm sure you'd be able to get them off your donor though.

bigblock73 · 02-06-2006, 11:39 PM

Quote:

Originally Posted by 72MARIO

I have a hard time understanding how this works. Page 5 is what I should be looking at for the directions ? Any specfic info on how to do this to our trucks ?

Mario, maybe this will help (I hope)

http://www.73-87.com/7387garage/exte...ight_relay.htm

Tx Firefighter · 02-07-2006, 12:27 AM

Quote:

Originally Posted by Premium72

where they show the "junction box" what is that...that the block on the passenger inner fender next to the battery tray?. this may solve the issues im having now. thanx. awesome write up.

It's a phenolic deal with a metal stud made into it.

A wire comes from the positive battery terminal to this block. From there, two wires travel across the core support and into the trucks wiring harness.

If you're having troubles in this area, check your fusible links. Use a testlight and also try to stretch them. Sometimes, a fusible link fails, but still looks fine. They go bad inside the insulation.

jhow66 · 02-07-2006, 01:21 AM

To Tex.: here is the item # for circuit breaker at NAPA--BK 7823105

jhow66 · 02-07-2006, 01:35 AM

By the way DO NOT use a fuse in your headlight circuit between the power source and your relays. Why? Pitch black road--75MPH-- hit a bump or whatever--light wire shorts and blows fuse--no lights and a curve coming up that you cannot see--ouch. Circuit breaker--lights goes out-comes back on -goes out and so forth. The circuit breaker in the light switch will protect the wires from light switch to the relays.

project1971 · 02-11-2006, 11:53 PM

Alright guys here is another source for a relay panel. I got mine from work actually, I work for Ford and had some wire looms laying around the entire things. Had some small relay boxes i had set aside for later projects and i ended up using one of them for my elec cooling fans (which also got from work they came off a wrecked Escape) They are in a plastic case with a removable top and you can replace the the relay if need be very easily. These can be found in most late model Ford vehicles like '97-03 F-150's. Inside the truck on the pass side under the panel on top of the dash is probably the easist to get to. I will take pic of it tomorrow and post them and pics of the cooling fans also they work great. I can have it sitting still running and turn the fans on and cools it so well the guage registers just below the normal level on the cold side! I have a box full of those relays I take them out of every fuse panel i replace to keep as spares or other projects.

project1971 · 02-12-2006, 01:42 PM

ok here is the pics i promised keep in mind they are off a Ford but who cares if it works right?!?

02-06-2006, 07:36 AM	#1
Tx Firefighter Watch out for your cornhole ! Join Date: Jun 2003 Location: Azle, Texas Posts: 14,162	Headlight relay mod revisited...my way to do it and save some money I was wandering around looking under the hood of junk cars, scavenging hose clamps and other usefull trinkets when I spotted the perfect thing. On a FWD Mopar puke car, late 80's, early 90's there is a perfect little bracket with two Bosch style relays on the fenderwell. These are the exact relays you need to do the headlight relay mod and not have to order them or buy them new. A Bosch relay is a Bosch relay. These were priced perfectly, free. Here's some pics of what I'm talking about... If you do this mod, please do it right, so it's reliable. I posted a picture of good quality crimping tools. Those 4 dollar do-it-all electrical tools suck. Spend 25 bucks and enjoy the good life. I also posted a picture of a neat tool I use. It's a miniature butane torch. I originally saw the Boyd's guys using them on TV. My wife picked one up for me at Home Depot. It's a godsend for heat shrink tubing in tight areas. Finally, there is a picture of a finished connection. Notice there are no connectors with colored plastic sleeves. Remove the sleeve and expose the bare connector. Then crimp with a good tool. Next, solder the connection to the terminal. Finally, cover with heatshrink. Matt covered the basics of this mod in his post, I'm just elaborating on a good way to do it even cheaper. Attached Images __________________ I'm on the Instagram- @Gearhead_Kevin Last edited by Tx Firefighter; 02-06-2006 at 07:38 AM.

02-06-2006, 10:59 AM	#2
70c10 67-72 Addict! Join Date: Feb 2002 Location: The TAX State! Posts: 7,857	Re: Headlight relay mod revisited...my way to do it and save some money Nice write up!. How did you know which terminals to hook up the headlight wires???. They look slick. __________________ Jim 1970 C/10 Fleetside w/Ghost Flames Lowered 4.5" front and 4" rear (Raked) 355/350 Turbo w/shift kit 10" Redneck Performance Verter w/2500 stall Hooker Super Comps part#2808-1 Performer RPM Air-Gap 12 Bolt w/3:73 gears- Eaton Posi Comp Cams XE262 with 1.6 Crane Energizers, Road Demon 625 and Brodix IK 180 heads

02-06-2006, 11:08 AM	#3
Tx Firefighter Watch out for your cornhole ! Join Date: Jun 2003 Location: Azle, Texas Posts: 14,162	Re: Headlight relay mod revisited...my way to do it and save some money Go here, and look at page 5. I just printed the page off for my tech notebook that I keep on my workbench. http://sonolithics.com/files/bosch.pdf Warning, not for the dial up guys, that's a big PDF file. __________________ I'm on the Instagram- @Gearhead_Kevin

02-06-2006, 11:57 AM	#4
Tx Firefighter Watch out for your cornhole ! Join Date: Jun 2003 Location: Azle, Texas Posts: 14,162	Re: Headlight relay mod revisited...my way to do it and save some money The sonolithics lists the terminal numbers on the relays, and if you look closely at the bottom of the relay themselves, the same numbers are on them. Also, I swapped the driver's side headlight plug for a spare passenger side plug I had laying around. Once you cut the original wiring apart, you will be left with two extra unused wires on the left headlight plug. The right headlight plug is exactly the same, but doesn't have the two unused wires hanging off of it. I did this strictly for a neater appearance. I didn't want two little short stubs of cut off wires sticking out and looking shoddy. __________________ I'm on the Instagram- @Gearhead_Kevin

02-06-2006, 12:25 PM	#5
shifty Questionable Join Date: Mar 2005 Location: Atlanta Posts: 13,376	Re: Headlight relay mod revisited...my way to do it and save some money Great stuff. Might want to include a link back to the original wiring explanation thread just for the purpose of archival. Curious - what car exactly did it come out of? (rough estimate?) i went to the junkyard today and just wanted to let everyone know - you can find the relay setup that Tex is talking about on 92-94 Dodge/Plymouth's : Sundance/Duster/Shadow models and I think also on the Summit as well. The relay setup is bolted to the driver's side shock/strut tower with what looked like a 1/2" or 13mm bolt. I seriously found at least 10 of them in good shape - and I didn't even make it all the way through the Mopar section of my local Pull-A-Part, so they are definitely out there to be had." __________________ If I've got anything up for grabs, it'll be here: 7-hole gauge cluster for a 67-72 p/u FREE (link) I can't check the forum daily. If I don't reply to you within 24 hours, drop me a PM! I'm (hopefully) still alive and will reply faster to a PM. Last edited by krue; 05-30-2007 at 11:26 PM.

02-06-2006, 12:42 PM	#6
Tx Firefighter Watch out for your cornhole ! Join Date: Jun 2003 Location: Azle, Texas Posts: 14,162	Re: Headlight relay mod revisited...my way to do it and save some money Late 80's or early 90's FWD Mopar with 2.2 or 2.5 engine. I think it was a Sundance or similar. __________________ I'm on the Instagram- @Gearhead_Kevin

02-06-2006, 12:47 PM	#7
jhow66 Registered User Join Date: Jun 2002 Location: Knoxville Tenn. Posts: 3,058	Re: Headlight relay mod revisited...my way to do it and save some money Here's how I set up my son's Blazer (orangeuavol). Attached Images __________________ 56 Chevy Bel-Air 2dr. HT (purchased new) 71 Chevy Cheyenne SWB PU (502HO) 65 GMC short bed step--work in progress and my gofer

02-06-2006, 05:54 PM	#9
Tx Firefighter Watch out for your cornhole ! Join Date: Jun 2003 Location: Azle, Texas Posts: 14,162	Re: Headlight relay mod revisited...my way to do it and save some money Mine are Klein brand. They cost 22 dollars a few years back. Worth every cent too. You can get them online for 20 bucks. http://www.mytoolstore.com/klein/1005.html __________________ I'm on the Instagram- @Gearhead_Kevin

02-06-2006, 06:52 PM	#10
72MARIO Registered User Join Date: Nov 2000 Location: Huntsville Ontario Canada Posts: 4,052	Re: Headlight relay mod revisited...my way to do it and save some money I have a hard time understanding how this works. Page 5 is what I should be looking at for the directions ? Any specfic info on how to do this to our trucks ? __________________ 1968 Suburban numbers matching all original truck now equipped with 6.0/4L80 on Accuair http://67-72chevytrucks.com/vboard/s...d.php?t=625017 1967 C/20 6.0/4L80 Roofing Truck 1990 V2500 Suburban "Plow Truck" 2005 TAHOE DD

02-06-2006, 06:56 PM	#11
Russell Professional Grade Join Date: May 2003 Location: Fort McMurray, Alberta Posts: 7,915	Re: Headlight relay mod revisited...my way to do it and save some money Oh, and here is how I did mine up: http://www.zieglerdigital.ca/public/...tricfans01.jpg I haven't run the power wire from the firewall distribution block to the core support dist block yet, but other than that, its all ready to go. Still plan to buy an H4 European style bosch headlight conversion kit for the truck yet, both sealed beams have one of their beams burnt out. I have an H4 kit in my 77, without the relays, and dang is it ever nice! Can't wait to see it done up with the relays! __________________ 1995 Chevrolet 2 Door Tahoe (6.6L LBZ Duramax / ZF6 / NP241 with 1 ton solid axle swap) Last edited by Russell; 02-06-2006 at 06:56 PM.

02-06-2006, 07:29 PM	#13
roger0080 Registered User Join Date: Nov 2000 Location: Carver County, Minnesota, USA Posts: 626	Re: Headlight relay mod revisited...my way to do it and save some money TxFirefighter, did these have any female plastic connector housings attached to the relays from the MOPAR donor car or did they attach like you show in the photo? __________________ 72 Chev C-10 90% restored (former AZ truck) ... 71 Chev K-20 Cheyenne my vacation crusier... 72 Chev C-10 Now retired and striped after many faithful miles... 72 GMC 1500 Retired to the junk yard after bought new in '71...

02-06-2006, 08:28 PM	#14
Tx Firefighter Watch out for your cornhole ! Join Date: Jun 2003 Location: Azle, Texas Posts: 14,162	Re: Headlight relay mod revisited...my way to do it and save some money 72Mario. Basically, here's the deal. Power must travel from your battery all the way to the light switch then back to the lights. This induces a lot of resistance and voltage drop. The end result is that far less than battery voltage reaches the lights, causing them to not be as bright as they could be. The relay mod changes all this. It makes it to where the power only has to go from the battery through the relay on the core support and then to the headlights. This is a much shorter pathway with fewer sources of resistance. The end result is full battery power reaches the headlight and that gives 30 to 50 percent improvement in headlight output. Mad electrical has a great article on their website which explains this fully, in easy to understand language. __________________ I'm on the Instagram- @Gearhead_Kevin

02-06-2006, 08:34 PM	#15
Tx Firefighter Watch out for your cornhole ! Join Date: Jun 2003 Location: Azle, Texas Posts: 14,162	Re: Headlight relay mod revisited...my way to do it and save some money Here is the link to MAD's article. There are two pages with lots of pictures. http://www.madelectrical.com/electri...adlights.shtml Roger, the Mopar used a nice plug with the wires securely positioned. Only thing was, the owner had stripped this car of it's entire wiring harness. So, I was able to get the relays, but not the connectors. I'm sure you'd be able to get them off your donor though. __________________ I'm on the Instagram- @Gearhead_Kevin

02-07-2006, 01:21 AM	#18
jhow66 Registered User Join Date: Jun 2002 Location: Knoxville Tenn. Posts: 3,058	Re: Headlight relay mod revisited...my way to do it and save some money To Tex.: here is the item # for circuit breaker at NAPA--BK 7823105 Attached Images __________________ 56 Chevy Bel-Air 2dr. HT (purchased new) 71 Chevy Cheyenne SWB PU (502HO) 65 GMC short bed step--work in progress and my gofer

02-07-2006, 01:35 AM	#19
jhow66 Registered User Join Date: Jun 2002 Location: Knoxville Tenn. Posts: 3,058	Re: Headlight relay mod revisited...my way to do it and save some money By the way DO NOT use a fuse in your headlight circuit between the power source and your relays. Why? Pitch black road--75MPH-- hit a bump or whatever--light wire shorts and blows fuse--no lights and a curve coming up that you cannot see--ouch. Circuit breaker--lights goes out-comes back on -goes out and so forth. The circuit breaker in the light switch will protect the wires from light switch to the relays. __________________ 56 Chevy Bel-Air 2dr. HT (purchased new) 71 Chevy Cheyenne SWB PU (502HO) 65 GMC short bed step--work in progress and my gofer



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02-11-2006, 11:53 PM	#20
project1971 Registered User Join Date: Apr 2003 Location: Oklahoma City Posts: 605	Re: Headlight relay mod revisited...my way to do it and save some money Alright guys here is another source for a relay panel. I got mine from work actually, I work for Ford and had some wire looms laying around the entire things. Had some small relay boxes i had set aside for later projects and i ended up using one of them for my elec cooling fans (which also got from work they came off a wrecked Escape) They are in a plastic case with a removable top and you can replace the the relay if need be very easily. These can be found in most late model Ford vehicles like '97-03 F-150's. Inside the truck on the pass side under the panel on top of the dash is probably the easist to get to. I will take pic of it tomorrow and post them and pics of the cooling fans also they work great. I can have it sitting still running and turn the fans on and cools it so well the guage registers just below the normal level on the cold side! I have a box full of those relays I take them out of every fuse panel i replace to keep as spares or other projects. __________________ 2008 Ford FX2 Screw 1971 C10 project in shop now! 2004 Pontiac Grandam (wifes) 2000 Cavalier z24 (gas saver)

02-12-2006, 01:42 PM	#21
project1971 Registered User Join Date: Apr 2003 Location: Oklahoma City Posts: 605	Re: Headlight relay mod revisited...my way to do it and save some money ok here is the pics i promised keep in mind they are off a Ford but who cares if it works right?!? Attached Images __________________ 2008 Ford FX2 Screw 1971 C10 project in shop now! 2004 Pontiac Grandam (wifes) 2000 Cavalier z24 (gas saver)

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