I have done this mod and have had it running for a couple weeks.. Since doing this mod I have occasionally had both turn signals come on when using the left turn signal only. Not sure how the parking lights got involved since I have no connections to the parking lights...
I won't duplicate this on the other threads about the different years but It is a bad idea to do this in this manner. The positive lead is common and the BCM pulls down the relay's negative side of the coil. The BCM outputs have a limit on the current they can handle and I suspect GM never intended to have more than relay controlled in this manner. I do not know what the current limitations are for the BCM and I am sure GM over engineered them if we have 4 EXTRA relays running off one output but I am rethinking how this should be done.
If you do this mod and your truck starts acting weird or you Blow your BCM you have been warned...
To PROPERLY do this mod insuring no BCM damage I believe requires some wiring beneath the fuse panel and requires the addition of a new relay wired in parallel to the current one for each light you want to have on. (Low beam, DRL, Fog)
Use the posting I had earlier about the pin usage of the relays and identify what each pin does.
I should look up the wiring on each of the relays and offer the proper wiring but I won't do that until I do this myself.
Basically you need to wire the new relay so the switched contacts 30/87/87a are wired to the same wires as the same pins on the factory relays. You need one relay for each light you want to turn on, for all of the lights to be controlled you need 3 relays. (High beam is a "trigger" so it doesn't need a relay)
Chose either pin 85 or 86 to be the ground and the other to be the +12. Should not matter which is which.
Ground your ground pin on all of your added relays to the body. (Use a star washer between the body and your connection. A soldered or crimped connector is the best connection to the ground wires is best option here. Very little power goes through this wire so you don't need a big one.) (up to 3).
For the positive lead you need to pull this from the switched side of the relay you want to feed from. (Ex. The High beam light... Use the lead from the 30/87/87a pins that is positive ONLY when the lights are on.) If you are going to do more than one "trigger" you need to isolate them with Diodes with the line on the diode pointed in the direction of the relay you are switching.
So assuming you want to do the all on high mode you will run a lead from the high beam switched to all of the relays without need of a diode.
If you want to run the full time DRL along with all on high you will need to also run the DRL from the low beam but you will need diodes on the leads from the high beams and the low beam to the DRL relay so that when the low beam only is on it doesn't back feed to the high beams and light them up. Not to mention will likely blow a fuse since the low beam circuit is not large enough to run both low and high beams.
This works because now you are running the lights off the powered relays and NOT the BCM. This thus protects the BCM from potential damage and all of your lighting should work without issue. I have some small DEI security relays that I will use for this. No need to use the large 30/40 amp relays. The MOST you are going to pull, assuming 65 watt bulbs can be figured easily. 65x2 (for 2 65 watt brights) = 130 and 130 / 12 = 10.8 (For figuring amperage draw the formula is Watts / Volts = Amperage so in this case it ends up being 10.8 amps at 12 volts) So a small 20 amp relay such as those from DEI will work just fine. You can also look at the relays in the circuit and see they are small as well. The DEI ones are real nice because they are compact and already prewired.
I should also note that by wiring the relays in parallel with the original factory ones you are preserving the original factory operation and just adding to it. When the add on relay is on it will not affect the factory relay in any way and vise versa. However someone might get confused if they pull the factory relay and the lights still light up...
At some point this summer I will do this mod myself and document with wire colors and pictures.
I won't duplicate this on the other threads about the different years but It is a bad idea to do this in this manner. The positive lead is common and the BCM pulls down the relay's negative side of the coil. The BCM outputs have a limit on the current they can handle and I suspect GM never intended to have more than relay controlled in this manner. I do not know what the current limitations are for the BCM and I am sure GM over engineered them if we have 4 EXTRA relays running off one output but I am rethinking how this should be done.
If you do this mod and your truck starts acting weird or you Blow your BCM you have been warned...
To PROPERLY do this mod insuring no BCM damage I believe requires some wiring beneath the fuse panel and requires the addition of a new relay wired in parallel to the current one for each light you want to have on. (Low beam, DRL, Fog)
Use the posting I had earlier about the pin usage of the relays and identify what each pin does.
I should look up the wiring on each of the relays and offer the proper wiring but I won't do that until I do this myself.
Basically you need to wire the new relay so the switched contacts 30/87/87a are wired to the same wires as the same pins on the factory relays. You need one relay for each light you want to turn on, for all of the lights to be controlled you need 3 relays. (High beam is a "trigger" so it doesn't need a relay)
Chose either pin 85 or 86 to be the ground and the other to be the +12. Should not matter which is which.
Ground your ground pin on all of your added relays to the body. (Use a star washer between the body and your connection. A soldered or crimped connector is the best connection to the ground wires is best option here. Very little power goes through this wire so you don't need a big one.) (up to 3).
For the positive lead you need to pull this from the switched side of the relay you want to feed from. (Ex. The High beam light... Use the lead from the 30/87/87a pins that is positive ONLY when the lights are on.) If you are going to do more than one "trigger" you need to isolate them with Diodes with the line on the diode pointed in the direction of the relay you are switching.
So assuming you want to do the all on high mode you will run a lead from the high beam switched to all of the relays without need of a diode.
If you want to run the full time DRL along with all on high you will need to also run the DRL from the low beam but you will need diodes on the leads from the high beams and the low beam to the DRL relay so that when the low beam only is on it doesn't back feed to the high beams and light them up. Not to mention will likely blow a fuse since the low beam circuit is not large enough to run both low and high beams.
This works because now you are running the lights off the powered relays and NOT the BCM. This thus protects the BCM from potential damage and all of your lighting should work without issue. I have some small DEI security relays that I will use for this. No need to use the large 30/40 amp relays. The MOST you are going to pull, assuming 65 watt bulbs can be figured easily. 65x2 (for 2 65 watt brights) = 130 and 130 / 12 = 10.8 (For figuring amperage draw the formula is Watts / Volts = Amperage so in this case it ends up being 10.8 amps at 12 volts) So a small 20 amp relay such as those from DEI will work just fine. You can also look at the relays in the circuit and see they are small as well. The DEI ones are real nice because they are compact and already prewired.
I should also note that by wiring the relays in parallel with the original factory ones you are preserving the original factory operation and just adding to it. When the add on relay is on it will not affect the factory relay in any way and vise versa. However someone might get confused if they pull the factory relay and the lights still light up...
At some point this summer I will do this mod myself and document with wire colors and pictures.