How-to: Rigid Dually Reverse Lights Install - Picture Heavy
10-08-2014, 02:28 PM
#73
Senior Member
Because the wire and fuse to the reverse lights are not designed for extra load and could blow the fuse or start a fire. You can get away with very low wattage, LED for example, but it is not an ideal solution for standard bulbs. That's why you use a relay. You grab a low voltage signal off the brake lights to trigger the relay, but get your power from the battery. In my case I just used the trailer harnes power.
10-12-2014, 06:23 PM
#74
Senior Member
Thanks Benchwarmer....I knew something was up! The dual 87 pins explain it. Seems like you know more than the two of us put together! Appreciate you helping out.
I think the KC relay with the dual 87 pins may be non-standard. All the ones I looked at online and locally had both 87 and 87a pin outs.
If anybody is following along at this point, the standard automotive 5-pin relay with pins 87 & 87a should be wired as follows:
Pin 87 – Connected directly to battery, protected by 15A fuse.
Pin 30 – New B/U Lights, positive wire
Pin 86 - ground (or neg terminal on battery)
Pin 85 – Original Truck B/U lights, positive wire
Pin 87a – Power wire from the switch in the cab
I think the KC relay with the dual 87 pins may be non-standard. All the ones I looked at online and locally had both 87 and 87a pin outs.
If anybody is following along at this point, the standard automotive 5-pin relay with pins 87 & 87a should be wired as follows:
Pin 87 – Connected directly to battery, protected by 15A fuse.
Pin 30 – New B/U Lights, positive wire
Pin 86 - ground (or neg terminal on battery)
Pin 85 – Original Truck B/U lights, positive wire
Pin 87a – Power wire from the switch in the cab
I also have another 5 pin relay with two 87 pins and no matter what combination I use I can't get the lights to work either.
As a general statement the lights work but I can't get them to work when I use either of the two relays.
They work with the switch OR in reverse, but NOT when the whole shebang is wired up.
10-12-2014, 07:20 PM
#75
Senior Member
So if you close the switch with it wired directly to the lights they come on; but when you try to hook it up to 87a the lights don't come on, is that right? That connection will be the easiest to troubleshoot because it doesn't rely on the relay coil at all to provide power, it's normally connected to pin 30. Where did you locate the relay and where/how did you tie into ground?
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Truckin (10-13-2014)
10-13-2014, 11:52 AM
#77
Senior Member
So if you close the switch with it wired directly to the lights they come on; but when you try to hook it up to 87a the lights don't come on, is that right? That connection will be the easiest to troubleshoot because it doesn't rely on the relay coil at all to provide power, it's normally connected to pin 30. Where did you locate the relay and where/how did you tie into ground?
that sounds correct. wife has the truck today so I cant trouble shoot it. I haven't mounted the relay yet because I wanted to make sure everything worked first. for the ground I used a wire directly to the negative post on the battery just to see if everything worked before I mounted it. is it possible that my ground wasn't secure? one time the lights worked with the in-cab-switch but they never worked while in reverse (with the relay connected).
10-13-2014, 07:55 PM
#79
Senior Member
that sounds correct. wife has the truck today so I cant trouble shoot it. I haven't mounted the relay yet because I wanted to make sure everything worked first. for the ground I used a wire directly to the negative post on the battery just to see if everything worked before I mounted it. is it possible that my ground wasn't secure? one time the lights worked with the in-cab-switch but they never worked while in reverse (with the relay connected).
Step 1, put +12 volts directly on the 87a pin and measure voltage at pin 30. This is the normally closed contact of the relay so the +12 volts should be on that pin when the relay coil isn't energized.
Step 2, you'll want to put +12V on pin 86 and ground on pin 85. While doing this, listen for a "click" inside the relay. It'll make that sound when the coil is energized and tries to move the internal switch from the 87a to the 87 pin.
Step 3, if the coil operated correctly pin 87 should now be connected to pin 30 (as long as you keep +12V on pin 86 and ground on pin 85.) Now you'll put +12V on pin 87 and measure pin 30.
