Headlight Relays

[baronbors]

After reading the article at http://www.madelectrical.com/electrical-tech.shtml , I decided to re-wire the headlights and fog lights using Radio Shack 12 volt relays. I obtained three of the 4 prong relays and then did a search on the site for possible threads on wiring. Didn't find anything relavent. It looks like two of the terminals on the relay are switched by applying current to the other two. I plan on running a 10 gauge wire from the battery ( 1 for each relay) to supply the current to the lights. The question I have is that it appears that the old power wires from the lights ( one for the low beam, one for the high beam and one for the fog lights ) go to the switch side of the relay and the other side of the switch go to ground. My concern is if I will be blowing a power fuse since there is no load on the switch and it shorts to ground?

[namba209]

Thom, I'm not sure what the RadShak relays are like, how do you plan on wiring them in the circuit? One relay each for hi-beam, and low beam and one for the fog lites? And if they are only a four prong relay, then you would have a 12V hi amp source in, one out when switched, a trigger or signal voltage in and the ground on the other two. Pretty simple as far as the relay goes, but you'd need a relay for both the hi and lo beam circuits and probably could use the hi-lo beam relay to trigger them. I'd have to do some more research and thinking about it to be sure. There would be no problem with using the power leads to trigger the relay, there will be very low amps used, just enufff to energinze the relays. So it shouldn't have any affect on blowing the fuses. It won't be a direct short to ground at all. HTH.

[69GTLEE]

Tom it sounds to me like you have a wire hooked up wrong the relay should draw less than an amp and not blow the fuse.
Ron is right you will need one relay for hi beams and one for low beams.
If the relays are wired right you should hear a click when they energized

Lee

[soybean]

Originally Posted by baronbors After reading the article at http://www.madelectrical.com/electrical-tech.shtml , I decided to re-wire the headlights and fog lights using Radio Shack 12 volt relays. I obtained three of the 4 prong relays and then did a search on the site for possible threads on wiring. Didn't find anything relavent. It looks like two of the terminals on the relay are switched by applying current to the other two. I plan on running a 10 gauge wire from the battery ( 1 for each relay) to supply the current to the lights. The question I have is that it appears that the old power wires from the lights ( one for the low beam, one for the high beam and one for the fog lights ) go to the switch side of the relay and the other side of the switch go to ground. My concern is if I will be blowing a power fuse since there is no load on the switch and it shorts to ground?

No, it should work as you want it to. I wired all my lights using mad electrical relays and the original switch energizes the relay, the high current draw comes from a terminal block from the battery. Run the ground wire as described. The only recomendation I would make would be to run a fusible link on the high current draw side of the battery to the relay.
So I wouldn't have a lot of wires running around in the engine compartment, I ran a terminal block to feed the relays. If you want, I can take a picture of mine to help make some sense out of the above. It can be confusing. HTH, Jarrell

[markandson]

If you use a double throw relay, (one set of contacts closed normally and another set of contacts closed when energized) then you can use it for both high and low beam. If it is a sprung relay, that is, it returns to a normal condition when un-energized, rather than staying where it was last switched to, then just wire the low beam to the un-energized side. When you turn the lights on they will always come on in the low beam state. All you do is wire the high low beam switch in the car to this relay. If you understand what a relay does it is extremely simple. It's just an electro-magnet operated switch.
Two of the inputs are for the magnet, one ground and one that gets switched on and off to energize and de-energize. The other terminals will all be for contacts, either normally closed or normally open, depending on what relay you buy. The rating of the relay is associated with the size of the contacts inside the relay. The voltage is the voltage it takes to operate the electro-magnet. Simple....see...

[baronbors]

Originally Posted by soybean No, it should work as you want it to. I wired all my lights using mad electrical relays and the original switch energizes the relay, the high current draw comes from a terminal block from the battery. Run the ground wire as described. The only recomendation I would make would be to run a fusible link on the high current draw side of the battery to the relay. So I wouldn't have a lot of wires running around in the engine compartment, I ran a terminal block to feed the relays. If you want, I can take a picture of mine to help make some sense out of the above. It can be confusing. HTH, Jarrell

Picture would be great- I was planning to run separate wires from the battery for the three relays but if a single run works to the terminal block and then three runs to the relays with a 30 amp inline fuse for each - this should cover it- right?

[soybean]

I'll take a picture around lunchtime and post it. Now, what Jeff said makes sense too and would cut down on the use of one relay if I'm correct. Jarrell

[markandson]

Check this quick sketch out. I think it is correct. The existing Headlight relay could be used as the power relay if you wanted to. I didn't look but I would think that this is the way the car is set up from the factory. It already has two relays controlling the headlights. The only thing not shown is the high low light on the dash, sorry I forgot. I included both a pdf and a jpg. The pdf took out a couple of the i"s for some reason, you'll just have to use your imagination.

[soybean]

Tom, here's the picture of how I wired my lights, fuel pump and Inertia Switch. All are powered by the terminal block indicated. I spliced into the harness in the engine compartment and found the High/Low wires and used them to energize the relays. All the relays are run from the terminal block using fusible links. One of our club members (BQ97) has enclosed his in a small project box and made it look real nice. What you see is a rats nest to my eyes and needs tidying up. But, it's a daily driver. The next one will have the relays out of sight. HTH, Jarrell

[namba209]

Jarrell and Jeff, both you guys are showing the "Bosch" type relays, Thom has or is using SPST relays, which is just a bit different although either will work, it's just in the wiring them in how they will work.

[baronbors]

Thanks Jarrell- that is what I am going to do. I am going to mount it up on the side of the radiator to keep the wiring as short as possible. I don't have working relays on the headlights so the switching is already modified and goes through the fuse block to my dash. When I turn on my halogens the charging meter pegs out and the orange light comes on . Plus the halogens are only a little brighter than the original lights and the fuses get nice and hot because of the draw. Hope this will allow more power to the lights and make them much brighter. Did it work well for you?

BTW- the relays I got at Radio Shack are for auto use and look exactly like the ones you used.

[soybean]

I also did the 1 wire alternator upgrade at the same time and the difference was substantial. Lights were brighter and electrical things seemed to work better. I was also worried about melting down the fuse box, which prompted me to go to the relays to handle the current draw. Better a few bucks than a major rewire. I wish at the time I had known about the 105 amp alternator that guyopel has found, but the 65 Amp seems to be more than adequate. The reason I went with Mad electricals' products was that it was all in one package. All the connections were pretinned, the heatshrink tubing was included, etc. A little pricey, but I believe it was well worth it. HTH, Jarrell

[markandson]

Ron,
spst just stands for a generic term "single pole single throw" which means basically it is just and on off switch. The other choices are combinations of single/double throw and single/double/triple.... pole. Doesn't matter who makes it, just what you have as far as specs go.

[namba209]

Yeah Jeff, you're right, I was just looking at what you said and drew up, plus what Jarrell has in his pics. From what Thom said his relays were only 4-wire and the ones you referred to and what Jarrell shows are 5-wire, commonly referred to as "Bosch" type. I'm using 6 of those on Willit? to spread the load and I had to revamp one to get the starting circuit working on both the start and run positions in my power panel. spaghetti factory. Didn't really think about it too much, at the time, my comp problems had my mind elsewhere. :o

[asdasc]

Hi Guys,

All this talk about relays got me to thinking about fixing the lights on my 70 GT. I just went out and using a voltmeter decided that the main headlight relay is bad. Jumping 12v to the high side of the coil wouldn't make it click. The ground is good. So, the question is: Is this a special relay or can I get it at any autoparts place? If so, what do I call it? If not, where is the best spot to get one?

Thanks,
Steve

[markandson]

I have not opened one up yet to see what makes it tick. I doubt there is anyone in an auto parts store who will take the time to cross ref somthing for you. Best bet is to ask here, I am sure there are many available. I have one extra one. If no one else can help maybe you can beg me to part with it.

[namba209]

Steve, I'm not knocking your expertise here, but knowing the location of the relay and all the wires attached, are you sure you jumpered the right terminal? With a good ground at the brown wire, terminal 86, and 12 volts applied to the YellowBlack wire from the headlite microswitch at terminal 85, the relay should close and all the lites should come one. Applying 12 volts to the red wire on terminal 30/51 won't do anything to make the relay function. That wire supplies 12 volts to all the other lites through the relay contacts. HTH.

[asdasc]

Hi Ron,

I think I have it right. I confirmed that I have 12v at the red wire on 30/51. I then confirmed that when I flip over the cans, I can make 12v appear on the YellowBlack wire, without a click or any lights coming on. When I then Jumper from the red to each of the wires on connectors labled 87, the various functions come on, including the headlights.
One interesting thing is that the white light comes on and stays on when I flip the headlights open, until I jumper across and turn on the headlights, then it goes out, which makes sense.

Thanks,
Steve
By the way, Jeff, I am not ignoring your kind offer, I just feel bad taking your only spare. I found them on OGTS, but they are $45, which seems a little crazy. I work in the auto industry and will check my friends who have friends who make relays and see what I can get. I may also pull the cover and see what is making mine not work, it can't be too difficult to figure out!

[namba209]

Steve, great trouble shooting, that's exactly the way it is supposed to work, isolate the functions until you find the bad component. It definately sounds like a bad electromagnetic switch that is malfunctioning. It could be nothing more that one end of the coil wires being disconnected from the terminals inside the can. It can't hurt to pull the cover to check it out.

[baronbors]

Well- went and installed a relay for the low and one for the high headlights along with one for the fog lights. Man what a difference. Took me about 4 hours to re-do all the wiring but it really was worth it- I can't tell for sure but it looks like the headlights are about twice as bright. Well worth the $30 and the time involved. The Radio Shack auto relays worked great.

[baronbors]

Did an after dark run with the "Queen". Houston, we have power. The dim headlights are a thing of the past. YIPPEEE!!!!!

[namba209]

Well there now, Tom. By the sound of your post it appears you've eliminated a lot of resistance between the fuse panel and the headlites. And you know what resistance does to wires, don't you? Glad to hear your hard work paid off.

[soybean]

Originally Posted by baronbors Did an after dark run with the "Queen". Houston, we have power. The dim headlights are a thing of the past. YIPPEEE!!!!!

A lot of difference huh? Have you upgraded the headlights to Halogens? If you haven't, that's the next upgrade you should try. There is quite a difference there too. I am looking for the Cibies (sp?) with the Z beam. I've been told they are the best. Glad it worked out well. Jarrell

[baronbors]

Originally Posted by soybean A lot of difference huh? Have you upgraded the headlights to Halogens? If you haven't, that's the next upgrade you should try. There is quite a difference there too. I am looking for the Cibies (sp?) with the Z beam. I've been told they are the best. Glad it worked out well. Jarrell

I did that upgrade first hoping it would cure the dim headlight problem- it didn't. Went to standard H-4 's with the replacebal lamps- love em!

[baronbors]

Originally Posted by baronbors Did an after dark run with the "Queen". Houston, we have power. The dim headlights are a thing of the past. YIPPEEE!!!!!

Wife says the horns are louder too!