headlight relay thought

[73stallion]

was thinking last night about the H4 harnesses last night, the fact that they have a relay for low beam and high beam.

is there any reason why 1 relay couldn't be used for both? what i'm thinking of doing is interrupting the power going INTO the dimmer button on the floor, installing a relay in that wire, then it works for both low and high beams. would this work? if not why? would it overload the dimmer switch then?

 

[Viperwolf1]

If you only have 1 relay to supply power to low and high beams there would be no way to turn them off. You could use another relay to kill the power (from battery/fuse) and turn them off but what would you gain from that?

Power going through the dimmer just provides the signal to turn the relay(s) on. The switched high current power needs to come from a fused battery (constant) source.

 

[73stallion]

you missed what i'm saying. the relay would be in the power wire BEFORE it goes into the dimmer switch (not the headlight switch in the dash) so it'd work for both high or low beam. this is instead of having to run 2 relays AFTER the dimmer. it'd still turn on and off with the headlight switch.

 

[Viperwolf1]

Oh. That could work technically. I think the dimmer has some heavy contacts. The only issue I see with that is you would have to upgrade the wiring from the relay to the headlights (grounds too) if you still have the stock harness. The factory stuff is very small and it would become a bottleneck.

 

[oleguy74]

lite sw relay

this would be ok.it would lower current through lite sw.but useing h4's,dimmer sw might be taxed.relay would need to have 70-80 amp contacts.all in all two relays are better.

 

[Justafordguy]

I agree that two relays are better and the pre-made kits are easy to install and cheap.

 

[73stallion]

cheap? at $60? i can get a $6 relay and a $4 roll of wire, saves me $50. on my budget any way i can save money and still get good results i'll try and do it. worst case i'll remove the relay and splice the wire back together if it doesn't work, not much lost. not trying to cheap out or be a PO, just trying to get results on a budget.

 

[70_Steve]

I thought the reason for installing the relays was to eliminate the voltage drop created by the small guage wire run from the fuse panel to the headlight switch, then to the dimmer, and on to the headlights. If you put the relay before the dimmer, it only eliminates half the problem.

I've got my H4's running off of the stock wiring. They're much brighter than the stock headlights, so I'm happy. If you're on a budget, and the headlight switch circuit breaker's not cutting out on you, why even bother putting in a relay?

 

[Justafordguy]

I just bought 2 @ $29 each. I plugged them in in 5 minutes, Done.

If you have plenty of time, they are really easy to build but the kit is just so easy. I figured I could save maybe $10 but my time is worth way more than that.

 

[73stallion]

I thought the reason for installing the relays was to eliminate the voltage drop created by the small guage wire run from the fuse panel to the headlight switch, then to the dimmer, and on to the headlights. If you put the relay before the dimmer, it only eliminates half the problem.

I've got my H4's running off of the stock wiring. They're much brighter than the stock headlights, so I'm happy. If you're on a budget, and the headlight switch circuit breaker's not cutting out on you, why even bother putting in a relay?

because the breaker in the light switch IS tripping. you're right about only eliminating half the problem, but i've never heard of a dimmer switch burning or tripping because of higher power lights. this is just to take some load off the light switch so the breaker will stop tripping.

I just bought 2 @ $29 each. I plugged them in in 5 minutes, Done.

got a source on the $29 harnesses? you got my attention.

 

[70_Steve]

because the breaker in the light switch IS tripping. you're right about only eliminating half the problem, but i've never heard of a dimmer switch burning or tripping because of higher power lights. this is just to take some load off the light switch so the breaker will stop tripping.

Well, you've got a specific problem, and a reasonable fix, and it's only $10!!!! I say go for it! Take some pics of where you mount the relay.

got a source on the $29 harnesses? you got my attention.

Hmm. I'd be interested, too!

 

[canrel]

this would be ok.it would lower current through lite sw.but useing h4's,dimmer sw might be taxed.relay would need to have 70-80 amp contacts.all in all two relays are better.

70-80 amp contacts? Where are you getting the 420 watt bulbs?

65 watt high beam in 12 volt system should pull about 5.5 amps
per bulb. 15 amp switch, relay, is plenty.

 

[Broncobowsher]

So you want to keep the low beams on and add high beams instead of actually switching filiments.

Bad. Not the wiring or the relays. The bulbs themselves. That is too much heat for the bulb. they are not designed for it. I even remember seeing a service bullitain for police upfitting that stated to prevent that from happening and that was just for flashing high beams, not holding them on. I am sure it will work for awhile, but I would expect to see reduced bulb life from it.

 

[oleguy74]

70-80 amp contacts? Where are you getting the 420 watt bulbs?

65 watt high beam in 12 volt system should pull about 5.5 amps
per bulb. 15 amp switch, relay, is plenty.

that is true.did not mean to imply that maybe lower rating would not work.but still go with 20 amp contacts.

 

[oleguy74]

So you want to keep the low beams on and add high beams instead of actually switching filiments.

Bad. Not the wiring or the relays. The bulbs themselves. That is too much heat for the bulb. they are not designed for it. I even remember seeing a service bullitain for police upfitting that stated to prevent that from happening and that was just for flashing high beams, not holding them on. I am sure it will work for awhile, but I would expect to see reduced bulb life from it.

in my post#5 the relay would just put power to the dimmer sw just like the lite sw.the main diff is the lite sw would only see the current of the relay not the lites.just rember the power source from relay contacts must be non-switched power.good or bad I just showed how to do it...only one filliment would be on at a time.high or low.

 

[Broncobowsher]

OK, got it now. Pictures sometimes have issues on the work computer.
Full current through the dimmer. Headlight switch only power the relay.

I have found that dimmer switches to often be a weak link. I have delt with enough old rides where the dimmer switch would turn off the lights when switched and a little frantic floor pounding was needed to cycle the switch enough for the contacts to finally make decent contact and the lights to stay on. Personally if I were going to go and do a relay, I would go ahead and just do 2. Keeping the dimmer switch handling full current and you still have half the potential problems.

 

[oleguy74]

my thoughts also.

 

[MarsChariot]

I just bought 2 @ $29 each. I plugged them in in 5 minutes, Done.

If you have plenty of time, they are really easy to build but the kit is just so easy. I figured I could save maybe $10 but my time is worth way more than that.

I would like to see that. I thought that I would be really smart and make my own plug-in relay harness and ended up spending $85 by the time I collected all the parts to do it really professionally and then had to spend my time building it, too.

Yes, the pre-made relay kits are a steal.

 

[73stallion]

well an update, installed the relay yesterday and it worked great. he had to use his lights on the way home and no problems with them going out now.

 

[Justafordguy]

got a source on the $29 harnesses? you got my attention.

I got them from LMC. I put one on the EB and one on the 70 Mustang. It takes like 5 minutes to install. It makes the lights brighter also.