Reverse Electric Lockout Not Working on Trailer and 2010 BMW X5 with OEM Wiring Harness

Question:

I have a 2010 BMW X5 with the 7 pin OEM wiring harness and am pulling a trailer with the flat 5 pin connector. The reverse lights are hot on the center pin of the 7 pin harness and I can verify voltage 12.5 at the output of the 5 pin adaptor which powers the solenoid to release the surge breaks. Having said this the surge breaks are not releasing. I hooked the trailer up to a friends tow vehicle and the surge breaks release when engaging reverse. Any suggestions on why the X5 would not disengage the surge breaks even though Im getting voltage output to the correct pin on the 5 pin connector? As my trailer has LED lights I have purchased the C35FR 7 to 5 pin adaptor for LED lights but have not tried it out yet. In addition to eliminating the light out warning would this adaptor have any impact on the reverse light circuit?

asked by: Dave C

Expert Reply:

You are correct about the bulb out sensor and the adapter # C35FR. There are load resistors built into the adapter to provide more load so that you do not get that sensor. The solenoid should have enough draw without it but it might help.

Since it works as it should when connecting the trailer to another vehicle that does sound like and issue on the vehicle side or with the adapter. Be sure to check that the output pin on the adapter matches the one on the trailer that leads to the solenoid just in case.

If the new adapter does not do the trick you may need an additional load resistor, # DI34ZR, on the solenoid wiring on the trailer to create more load since the power draw of the solenoid is low.

expert reply by: Michael H