New headlights installed -with pics

[boxrodz]

Originally Posted by Zoomad75

Email sent with my write up. I included Boxrodz schematic in addtion to my own. I don't have Boxrodz name to give credit where it's due so if he could chime in to get recognized for his drawing...

It's all good. You can leave the write-up as is.

Jeff-
If you would like the original-sized jpg, like it in a different format (for clarity) or (if any of you guys) would like something change or added to the diagram, just give me a heads up.

[bigblock73]

OK gang, I got zoomads article as well as Russels. While both these articles are very similar, they were also different in their approach to this mod and how they were written. I tried to combine the best of both of them into one, and here is my attempt. Please read this carefully and let me know if I left anything out. Pictures and schematics will be added once I get a page created for it.





If you have ever driven a 73-87 GM truck at night you know one thing, the stock lighting leaves something to be desired. Dull, dim yellow light just doesn’t cut it in today’s world with the latest advancements in lighting. Halogen bulbs that were the best you could get 10 or 20 years ago, but they cannot match the latest stuff coming out of Detroit on the newer cars and trucks. To improve your trucks lighting, options include upgrading to Silverstar sealed beams, or the latest trend would be replacing the sealed beams with an H4 conversion bulb. Both of the options will increase the light output, but not as much as possible due to the limits in the stock GM headlight wiring.

The stock headlight circuit is very inefficient for delivering voltage to the headlights. Power flows from the battery, through the firewall junction block, to the headlight switch, then to the hi/lo switch and then back out to the lights. Add up the total resistance of this circuit and you end up with less than the available system voltage. In my case on my 75 Blazer, the available voltage at the lights was over 1 volt less than the available system voltage measured at the alternator. This is why most lights on these trucks are dim, add any corrosion or other wiring issues and yours could be less.

Think about this. Assuming that 12.6 volts where you receive 100% of your light output, look at this quick comparison chart showing light output percentage as compared to the voltage the lights are receiving:

12.6 V = 100%
11.5 V = 75%
10.3 V = 50%
8.7 V = 25%

According to the chart, you’d only be getting approx 50% of your possible light output at 10.3 Volts!

To correct this problem and provide more voltage to the headlamps, a simple change can be made to the wiring. By adding relays to the system you can use the stock lighting circuits (hi/lo) to remotely turn on relays that are connected to direct battery power for the simplest circuit possible. Follow along and I’ll show you how I did this on my ’75 K5 Blazer.

LMC Truck now sells a kit to do this, but when I wanted to upgrade mine it was not out yet.

Keep in mind that my setup is for a ’75 model year and should work for all ’73 to ’80 single headlamp setups. It will work for single headlamp setups from ’81 and up also, but I have not verified the wiring colors on these trucks. Dual lamp trucks (4 total) work similar except for the fact that the high and low beam circuits go to separate bulbs.







Items you will need:

2 30 amp relays
2 30 amp inline fuse assemblies
2 rolls of 14 GA wire (2 different colors)
1 package of shrink tubing (for 14 GA wire)
1 package of female spade connectors (I got the weather proof kind with heat shrinkable ends) get at least enough for 4 connections at each relay!
1 package of ground eyelets

Tools you will need:

Wire cutters/strippers
Soldering iron and solder
Heat gun or lighter for shrink tubing/spade connectors


Here's what I did. I planned on putting the relays directly above and behind the d/s headlamp on the backside of the radiator support. I did this for two reasons, ease of access (not hidden by the battery) and it’s close to where the headlight wiring comes from the fender/cab. Knowing where I wanted to put the relays, I could set the length of wire I needed to power up each relay as well as the ground wires for the relays. I decided to pull the power from the junction block on the firewall (just above and to the left of the brake booster), as I hate having a billion wires tapped off of the battery. I routed the wires in the same split loom that the stock headlight wiring ran in on the inside of the d/s fender. This way it's all hidden except where I put the inline fuses nearest the junction block. To add the inline fuse holder to the circuit I spliced the wires, soldered the connection and covered the connection with the shrink tubing. I could then hook up the power wires to the 30 terminal on the relays (keep the fuses out so you don't have a hot circuit to play with). I then hooked up the ground wires I made up with the female spade on one end and the ring terminal on the other to the relays and ground on the radiator support.

Now we need to get the switched on signal to the relays and output to the lights. I cut the brown and green wires that led to the d/s headlamp (don't make the cut in the wires to the p/s bulb, see the important note below). Each wire is still used; just the relays will be in between the where the circuit was cut.

****VERY IMPORTANT: The stock headlight wiring is set up in a parallel circuit. If you notice at the d/s headlamp the lamp connector will have two of each wire (brown and green) going to it. If you peel back the conduit you will see that one set of the brown and green wires actually goes to the p/s headlamp. This is a clever little wiring trick the GM engineers did to eliminate having 4 wires from the dimmer switch to the lights. Still before and after this mod, if the d/s headlamp bulb fails the p/s light will stay lit. (Not like a cheap set of Christmas tree lights!)

With the brown and green wires cut, add the female spade connecters on both sides of the cut, on the switch side and the side going to the d/s light. Depending on where you made the cut, you might have to add a few inches to each side of the brown and green wires to allow enough slack in the wires for easy connection to the relays (try and use the same colors if you can to limit confusion later!). Following the schematic, you then hook up the brown wire from the switch side to terminal 86 on one relay and then the other brown wire to 87 terminal of the same relay. Do the same for the green wires to the same terminals on the other relay and you are done with the wiring. Secure the relays to the radiator support, making sure you got all connections tight and recheck your connections to the relays. You should have both brown wires to one and green to the other. If you have a brown and a green wire to each relay, your dimmer will work backwards. Stuff the wires back into conduit/split loom, put the fuses back in the inline holders and hit the switch. LET THERE BE LIGHT!

One thing I would like to change on mine after seeing the LMC harness is the connections to the relays. Having 1 connector with 4 terminals to the relay would look a lot cleaner than 4 individual spade terminals. Plus you would be less likely to reconnect it wrong if you ever had to replace a burnt out relay.

You can see the one major difference in my setup to the LMC kit is that you cut the wires to the d/s headlamp and use the existing headlamp wiring/sockets whereas the LMC kit does not have any cutting and supplies new wiring/sockets for the headlamps. This is your call if you want to cut your stock harness. The LMC kit is quickly reversible, take the stock headlamp socket from the LMC kit and plug it back to your headlamp to go back to stock. This is a bonus if you are out in the boonies and a relay quits. My setup can be changed back to stock, but you have to splice the two wires back together. I'll carry an extra relay with me if one was to fail.

One other thing, since my setup uses the stock wiring at the bulbs, you might be inclined to ask why with the smaller stock wiring? I used mine, because the stock wiring was free of any corrosion (benefits of Colorado not using salt in the winter) and the resistance was just as low as the same length of 14 gauge wires. That and the fact that the wiring for the p/s lamp was tucked well under the top of the radiator support and I was too lazy to fish it out. Basically, this is a judgment call for you to make. If your stock wiring is thrashed and corroded, rewire the lights with fresh wire and new connectors. Rewire it just like it was factory so you don't have two wires crammed into one terminal at the relay.

Overall, the modification is fairly simple to do and is inexpensive as well. You will be amazed at the increase in light output…even if you don’t upgrade to H4 bulbs. If you do plan on adding H4 conversion bulbs it is a worthwhile upgrade to get all the output possible from your new bulbs.

DISCLAIMER:
USE THIS AS A GUIDE. Your wiring colors may vary by year of truck. Use the GM service manuals for the stock schematics on the later trucks (Chilton’s or Haynes are not perfect in this area). If you don't have access to a Gm manual, break out the test light and verify the color/purpose of each wire your self.

[bigblock73]

boxrodz and zoomad75,

Can either of you please E-mail me the schematic jpgs you created? My E-mail is jdodge@73-87.com

Also, zoomad75, boxrods, and Russell...please send me the best (and your favorite) picture of your truck...I use it atop each article by the authors name. Also, please include your full name if you can in the E-mail

Thanks fellas!

[Zoomad75]

looks good. email sent! Thanks for hosting it for us.

[bigblock73]

OK, got the page put together. Like I said, I tried to combine both articles together the best I could...but ended up using mostly Rob's stuff. Here is the link...

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

Russell, I still have your stuff...and I appreciate you taking the time to do your part. I might end up putting together an article for your process as well...

Boxrodz, please send me a pic of your truck if you would be so kind, and your name as well...I would like to add it to the article.

Thanks again guys for your article and information, hopefully it will come in handy (again) in the near future for another 73-87 owner.

[Russell]

Like I said in the email, I don't need my article up there in its entirety to feel special inside

His is definitely the better writeup, so I seriously don't mind one bit

[boxrodz]

Originally Posted by bigblock73

boxrodz and zoomad75,

Can either of you please E-mail me the schematic jpgs you created? My E-mail is jdodge@73-87.com

Also, zoomad75, boxrods, and Russell...please send me the best (and your favorite) picture of your truck...I use it atop each article by the authors name. Also, please include your full name if you can in the E-mail

Thanks fellas!

Jeff-
Email sent.
It looks good. I did have a couple of minor suggestions. I also included a larger pic of the schematic as well as a modified one for the single headlamp setups.
Thanks again for the work that you, Rob and Russell have put into this.

[74Chevy74]

This is a great article, I'm getting ready to do this mod as well. I was poking around on ebay and found these, what do you guys think????

http://cgi.ebay.com/ebaymotors/ws/eB...MakeTrack=true

[boxrodz]

Originally Posted by 74Chevy74

This is a great article, I'm getting ready to do this mod as well. I was poking around on ebay and found these, what do you guys think????

http://cgi.ebay.com/ebaymotors/ws/eB...MakeTrack=true

But, it's hard to tell 'bout their quality from their picture.
They look alot like the Southern Rod and Parts Tri-Bars that Summit Racing sells. They go for about $30 each. The Tri-bars from Summit Racing look cleaner.

[DroppedZ84]

Just curious..but how many other "sealed beam" healight cars do you think this upgrade would be similar on? Makes ya wonder...Because some of my cars with sealed beam, the headlights LITERALLY SUCK!

[robsm88]

Old topic, but no one ever came to a conclusion if these tri-bar lights worked better. Found these on ebay.
http://cgi.ebay.com/ebaymotors/ws/eB...K%3AMEWA%3AVRI

[boxrodz]

Originally Posted by robsm88

Old topic, but no one ever came to a conclusion if these tri-bar lights worked better. Found these on ebay.
http://cgi.ebay.com/ebaymotors/ws/eB...K%3AMEWA%3AVRI

It's hard to tell from the pics, but I don't think those are tri-bars. They look like diamond headlights that use H4 bulbs. Don't know if they would be better, since they don't list the bulb wattage rating.

[badpeanut]

What are thoughts on using two 30A circuit breakers instead of two 30A fuses?

This way if you were flying down a dark road when something shorted at least you might get a flicker to guide yourself to a stop.

[boxrodz]

Originally Posted by badpeanut

What are thoughts on using two 30A circuit breakers instead of two 30A fuses?

This way if you were flying down a dark road when something shorted at least you might get a flicker to guide yourself to a stop.

It seems circuit breakers are popular among 4 by'ers. I imagine it's more convenient to flip a switch rather than fumbling to replace fuses. But, I'm not sure it buys you anything. Once the circuit trips, I'd figure the darkness is immediately welcoming you. In the end, if the circuit is tripping due to a short, it'll continue to trip until the short is corrected. What you could do is put each of the headlights on their own separate circuits (i.e relay for each low (or high beam) elements) that would isolate them from tripping simultaneously.