trailer brake blue wire voltage present error

[1 FMF]

i have a hayes g2 trailer brake in the truck, pulling horse trailer which has a break-away box with battery. sat for a year, pulled it home no problem. washed it this weekend and pulled it tonight and had this happen:
while stopped engine off key off trailer brake on (or engine can be running):
- touch brake pedal hayes g2 says blue wire voltage present, vehicle brake lights on but not trailer brake lights.
- turn on parking lights g2 says blue wire voltage present, no lights come on trailer.

i futz around with it and everything starts working, so i pull it down the road a few miles. as i'm driving the hayes will report no trailer then come back. then when i hit the brake i'll sometimes get blue wire voltage present error at which point if i turn on parking lights while driving i'll get no trailer lights. however when things are working i turn parking lights on while driving and all trailer lights come on then when i get the error either randomly or occasionally hitting brake pedal the trailer lights will stay on.

while driving i had the break-away battery connected, however all these errors will happen when parked with the battery not connected.
was wondering if anyone can verify from experience with certainty it's either the circuit board in the breakaway box or it's the breakaway switch before i cut wires. the way it was wired at the factory it's going to be a pain to redo there's no extra wire length to work with.

 

[Colt45ws]

I would check grounds. I dont know exactly how this is setup, but a faulty ground can cause all sorts of weird issues.

 

[eljefino]

I tend to agree, it's grounding thru the trailer ball which as you can imagine isn't always great.

 

[1 FMF]

my ground is white wire through the 7-pin connector.
i've redone the 7-pin receptable on the truck and that ground is good to the frame.

also, when i get this blue wire voltage present error the trailer brakes are NOT engaged, so that makes me think it's not the breakaway switch.

 

[1 FMF]

well, the cheap toolbag manufacturer sells the trailer with a 7-pin harness and a breakaway kit because it's a horse trailer. they used a basic 4-wire setup to the 7-pin plug and tapped off the brown wire for battery charging. that also explains why my trailer interior light will only work when i have the parking lights on (which i already figured). and now i know why the battery never seemed to be charged after using the trailer.