converting tail lights

Ok maybe I wasn't clear in my first post. THanks to all those who have offered advice so far.

My 2009 Suburban has the standard tail lights with one bulb for brake, one bulb for turn signal, and a bulb for reverse. This requires 5 wires to complete: ground, brake, turn, reverse, park. I am swaping out the entire tail light assembly with a new assembly from a Caddilac Escalade that is all LED (except for the reverse bulb). The issue is that the Escalade tail light uses the same LEDs for brake and turn signal. So it only requires 4 wires to complete: ground, brake/turn, reverse, park.

Since they also use different plugs I have gone ahead and assembled new plugs to go in between the body wire harness and the new Escalade tail light with a converter in the middle. I have also included a 50watt 6ohm resistor to simulate a turn signal bulb to prevent hyper flash (which is controlled by the BCM or Body Control Module). I can not just swap out a "flasher can" as it does not exist in this vehicle. I have installed a Hopkins 5 wire to 4 wire electronic tail light converter to make this work and only use one side of the output and it works fine. (Although one of the two converters I purchased was bad and wouldn't pass through the brake light feed.) Really the only thing I need to accomplish is how to pass the brake and turn through and output it as one. If the brake is applied it passes straight through. If the turn signal is applied it passes through and flashes. If the brake AND turn signal are applied it still flashes, but just alternate of the + feed (so it will have to be opposite of the front turn signal.)

I would like to be able to build my own by using a small circuit board and some diodes and relays and then stick it all in a small metal enclosure, but I am not exactly familiar in this area. I can solder and assemble fine but not so good with design. My end goal is to be able to build more of these in order to sell to other's wishing to do the same tail light conversion.

I know a simple automotive relay would "work" but I would like to make this as small as possible and also be as quiet as possible. I tried to break open the bad converter to see what all it had inside, but the way it is built is by pouring the rubbery plastic over their circuit board inside a mold so there is no good way to gain access to their circuit board.

Maybe I should have posted this in a different forum?

-=riggz

IMO you were quite clear. As I said it requires a DPDT relay (or SPDT and SPST), BUT that requires relocation of the flasher can AFTER the flasher switch. Where that can't be done, delay circuits are required and I've only used programmable stuff for that. (Hence my usual referral to commercial products.) PS - your flasher switch may feed +12V to "each side" of the BCM in which case the DPDT relay solution should work.

Hold off before buying relays etc. The above was written in haste and I'm about to haste off again. An SPDT should suffice since the front indicators are not involved. I was also thinking SPST tho I doubt it - I'll have to think about your set up. Do you know the current draw of the stop/flasher LEDs? The reason I ask is that a J-FET is perfect for this application, however they have limited current capacity - far too little for traditional bulbs - but I haven't investigated their use for LEDs. Also if you could confirm that your left-right selector switch supplies +12V to "either" input of the BCM. Ground switching can also be accommodated. However if it's a single wire control - ie, CAN-bus or other signalling - a simple relay-only solution is not possible.

hi, the turn signal switch supplies ground signals to the BCM, independent left and right inputs. info obtained on GM upfitter website. mark

THANKS Mark!! In that case, an SPDT relay.   (One per side if applicable.) 86 to fused +12V (see below**) 85 to flasher switch output or BCM input (eg, RHS) 30 to LED +ve 87a to switched brake +12V output 87 to BCM flasher output (eg, RHS) That assumes both brake and flash are +12V signals (not GND), but that should be true. And it assumes the BCM does not ground 85. I suggest a spike quenching diode across the relay coil - ie, a 1N4004 or 1N4007 between 86 & 85; line end to 86 - unless spikes are known to be harmless. ** I said 86 to +12V to allow hazard flashers with IGN off but that depends on how the hazards are switched AND means the relay will be energised whenever the flasher switch is to that side. If that's an issue, then 86 to IGN +12V (eg from the flasher fuse), but then that rear flasher might not flash with hazards on, and definitely not unless IGN is on. To explain the above operation assuming it's the RHS: - normally the brake +12V is connected to the tail LED - ie, 87a to 30. - when the flasher switch is in its RHS position it grounds the BCM as per normal, and 85 which thus energises the relay. - the energised relay switches the LED (30) to whatever the BCM is putting out its RHS to flasher lights (87). The ballast resistor could be placed anywhere from the respective BCM output to the LED +ve, but after 30 is probably better to it hyperflashes if the relay or circuit is faulty.