negative trigger from backup lights

Hello,

This is my first post.  I have searched the site so I hope this is nota duplicate post.  Sorry for the length.  Just trying to be complete.

I recently purchased a new boat trailer with disc brakes. The brakes

are surge brakes.   The system has a 5th wire (blue) that is to bewired into the backup light circuit.  This wire supplies power to asolenoid in the brake system to release the brakes when backing up. 

The backup lights in my vehicle (2002 Ford Escape) are activated by

closing a switch to ground when reverse is selected.  The + side ofthe backup ligh is hot when ever the ignition is switched on.

I researched the issue on this site and found how to wire a relay to

use the negative trigger to supply power to the brake solenoid.

I ran a fused 12 volt line from the battery and connected it to

terminals 86 and 30 of the relay.  I connected terminal 85 to thenegative side of the backup light and 87 to the blue wire to power thebrake solenoid. 

After connecting all the wires I checked the voltage and everything was

working as it should.  I was only checking the output voltage, I didnot have the trailer connected.  I then tied it all up with wire tiesand the next thing I knew, I had 12 volts on the output side (bluewire) all the time even with ignition off.  But the backup light wasnot lit.  The backup light continued to work as it should but thetrailer wiring had power through the relay all the time.  Somehow the relaywas getting a ground, yet the backup light was not seeing the ground.

I thought I had fried the relay but after disconnecting it and

testing, it works as it should.  I tried it all over again and thesame thing happened.

How is the relay seeing a ground when the backup light is not?  What am i missing here?

Thanks for you help

John W.

Farmington,Mi

Disconnect 85. 1) Is the relay still misbehaving? 2) Is that wire you disconnected at 85 seeing a constant ground? 3) Or does it only see a ground when you go into reverse? 1) Have you connected to 87a rather than 87? 2) If yes something wrong with your wiring or you have a short. 3) Diode 1N 4004 across the relay coil, band towards 86. Also line diode same type on 85 wire, band away from relay.

Thanks, will disconnect 85 and check relay behavour.

Wire to 85 is connected to backup light ground and only sees ground in reverse.  I put it in plastic loom to protect it.

John W.

Farmington,Mi

if you check, term 85 will show a ground with vehicle off, that is triggering the relay. can't connect term 86 to battery, needs to be connected to same power feed as reverse lights. you could connect terms 85 and 86 to the wires at the reverse light...orange / YELLOW +12 volt ignition, BLACK/ pink reverse (neg). or you can also find both at fusebox in left kick panel, they are in the same connector. mark

Mark,

I was wondering if it might be better to separate the circuit that powers the coil from the power feed. Iwill give this a try.  Thank You

John

John W.

Farmington,Mi

I did as Mark suggested.  Wired the relay coil to the back up lights (85 and 86), ran the power supply to 30 and took power off at 87.  It all works fine now.  Thanks

John

John W.

Farmington,Mi