Headlight Relay Switching, 1993 Chevrolet Blazer

Hello everyone,

I have a 1993 Chevy blazer K1500 and I want to use relays for switching on/off for the headlights to get the high amp draw away from the switch. I also want the headlights to have all 4 lights on when on highbeam. All the big names sell kits to do 1 or the other but not both. My question, is there a DIY way to do this easily or is there a way to mod one of the aftermarket kits to do it easy and efficient. The only way I could think of doing it was to use the signal wire from the highbeam relay to run both relays while high beam was on and add a diode in the circuit to prevent a backfeed to the low beam signal, probably wrong.

Any ideas would be welcome. Thanks to everyone in advance.

This thread will get both on with high beam

The above will get the 4 lamps on when on high beam. It will not be any extra load on your switch. Nothing more than the high beams are currently putting on it.

Are you having trouble with switches? If so, which portion, High or Low?

Thanks for the reply. I am not having any load problems with the switch, just trying to avoid switch problems and throw more light down the road. I have a 1970 Chevy K10 and I purchased and installed a relay kit without any problems.

I finally got around to my headlight project on the Blazer. I bought a harness kit with 4 pin relays that takes the power away from the switch and directly from the battery, but it only operates the normal factory way with 2 lights for lo beam and 2 lights for hi beam. I want to make it operate with 2 lights on lo beam and all 4 lights when the hi beams are switched on. The harness was pretty easy to install but I ran into problems when I tried to modify the harness to get all four lights to come on when the hi beams are switched. I tried to wire a diode ( to prevent current back feed ) in series to pass a positive signal to switch the lo beam. The hi beam relay switch signal was wired directly and I put another wire and diode ( to prevent back feed ) in series over to the lo beam signal wire so both relays would switch on when the hi beams were activated. When all of this was installed it resulted in the lo beams not coming on at all and the hi beams working only when they were switched on.
     Am I wiring it wrong? Am I using the wrong diodes? Magic Beans? In my mind it would work perfectly, in the 12 volt world, not so much. HELP!

I finally got around to my headlight project on my 1993 K1500 Blazer. I bought a harness kit with 4 pin relays that takes the power away from the switch and directly from the battery, but it only operates the normal factory way with 2 lights for lo beam and 2 lights for hi beam. I want to make it operate with 2 lights on lo beam and all 4 lights when the hi beams are switched on. The harness was pretty easy to install but I ran into problems when I tried to modify the harness to get all four lights to come on when the hi beams are switched. I tried to wire a diode ( to prevent current back feed ) in series to pass a positive signal to switch the lo beam. The hi beam relay switch signal was wired directly and I put another wire and diode ( to prevent back feed ) in series over to the lo beam signal wire so both relays would switch on when the hi beams were activated. When all of this was installed it resulted in the lo beams not coming on at all and the hi beams working only when they were switched on.
     Am I wiring it wrong? Am I using the wrong diodes? Magic Beans? In my mind it would work perfectly, in the 12 volt world, not so much. HELP!

Can you post a picture or drawing of how you have your relays/diodes connected?

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My ex once told me I have a perfect face for radio.

Sorry for the crayon drawing. It's all that I could come up with. I am using 4001 diodes and I can't remember the brand name of the harness or relays ( super cheap either ebay or amazon ) I crimped and adhesive heat shrunk both ends of the diodes to 1/4" male disconnect terminals so they could be flipped in direction of current flow. The diodes were tested with a multimeter and they are ok.

Looks good on paper. What voltage readings do you get when you backprobe the relay coils (leaving the relays connected) with low beams on/high beams on? Have you seen what happens if you swap relays?

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My ex once told me I have a perfect face for radio.

I have switched the relays and it made no difference. If I recall correctly, I would get full +12v before the relay and less than 1 volt at the relay. I am going to work on it tomorrow and will have better numbers

Let me explain differently. If you put one meter probe on terminal 85 of the low beam relay and the other probe on 86, what voltage reading do you get when you turn on the low beams? What about the high beams?

Trying to picture your "before and at the relay" almost sounds like you reverse biased a zener diode.

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My ex once told me I have a perfect face for radio.

I got it figured out and everything is working the way I want. Thanks for the replies (geepherder), they were very helpful and gave me the energy to stick with it.