H4 upgrade question...

[MAYHEM]

I just purchased a very clean and maintained 1994 Probe. I want to upgarde the headlights to H4. I did this same upgrade with my 77 280Z, to include 2 relays 1 for the low beams and 1 for the high beams. I noticed that in the haynes schamatics,that there is a relay that covers both head lights. Do you all spark chasers think it nessasary to still install 2 relays or should the one work? On the Probe fourm, a member did this same upgrade minus the double relay set up, so far no problem. The relay is to remove the load from the switch.

Cheers

 

[HTSS_TR]

Daniel Stern has a very article about adding relay to exiting wiring system.
http://www.danielsternlighting.com/tech/relays/relays.html

 

[MAYHEM]

Originally Posted By: HTSS_TR
Daniel Stern has a very article about adding relay to exiting wiring system.
http://www.danielsternlighting.com/tech/relays/relays.html


Thanks for the info,HTSS_TR. I noticed in his diagrams the first one does not have any relay, and he added 2 one forthe hi and one for the low, that what I did on the 77 280Z. Now on my '94 Probe, there is a factory relay that covers bothhi and low. I want to know if the one relay would surfice fo the mod?

Cheers

 

[HTSS_TR]

His first diagram shows original wiring from factory without relay. If there is a relay from factory for the '94 Probe, then you can keep that relay for high beam and add second relay for low beam only.

But to confirm this idea, you should contact Daniel Stern by email he would tell you what is the best way to upgrade your wiring with 1 or 2 relays.

 

[moribundman]

First of all you have to figure out how many Amps your lights will draw, and you must choose the relays and wire gauge appropriately.

Amps = Watt/Volt
For example 2x 55 W = 110 W
110/12=9.1

Automotive relays are commonly rated for 30 A. So yes, usually you can easily get away with one relay for two lights (with street-legal Wattage), but one relay per headlight adds welcome redunancey. While relays don't fail very often, you can reduce the chance of being left in the dark considerably by having one relay per headlight. That's why in case of the low beams I would go with one relay per headlight.

An H4 bulb contains one low beam (55 W) and one high beam (65 W) filament.