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View Full Version : Tapping in trailer plug to car loom


Lionelgee
27th July 2018, 06:12 PM
Hello All,

Blowing my brake lights on my Commodore every time I hooked in a trailer plug caused me to investigate how the car end of the trailer plug was wired into the loom. In the past the vehicles I have owned had the trailer plug wire joined in at the loom before the wires led to the indicator and brake lights. I thought that this was standard practice.

What I found when I took the interior covers off was the trailer plug wires were cut into the indicator wires just a couple of centimetres before the bulb fits into the lens body. Is this the new standard practice for the auto-electrical industry; or is it a previous owner's hack job?

My daily driver is a VY Commodore Wagon.

I reckon the problem is in the car. I have two separate boat/trailer indicator boards, plus I have tried the trailer's individual wiring. I have checked each unit and none of the three systems has a fault. Nor, did they cause any problems with my previous car. However, as soon as the trailer plug is inserted into the car female fitting and the ignition is turned on - the fuse for the brakes blow.

Should the trailer wires be hooked in via the loom before the wires start branching off to the various indicators or am I just being too "old fashioned"?

I did not check to see if the wire joints were soldered or just clipped in. I just checked the wiring for any obvious problems. Then I saw how the wire joints were arranged. I shook my head and put the covers back on. It is not going to be a quick job to fix. Plus I thought I would seek some advice first.

Kind regards
Lionel
Tombie
27th July 2018, 06:20 PM
Grab a multimeter and work out the pin outs on the Commo’

Once you know how that’s wired you have a beginning.


Cutting and soldering in before the socket isn’t a hack, depends where the loom allows access. IMO cut in and solder is better than Scotch Locks, which should be banned [emoji41]
87County
27th July 2018, 06:51 PM
Grab a multimeter and work out the pin outs on the Commo’

.....

. IMO cut in and solder is better than Scotch Locks, which should be banned [emoji41]


I came across an ARB installed bullbar where scotchs had been used - most unprofessional and unreliable
Lionelgee
27th July 2018, 07:05 PM
Grab a multimeter and work out the pin outs on the Commo’

Once you know how that’s wired you have a beginning.


Cutting and soldering in before the socket isn’t a hack, depends where the loom allows access. IMO cut in and solder is better than Scotch Locks, which should be banned [emoji41]

Hello Tombie,

To get to the loom before the sockets requires the removal of two trim clips and two screws. I suppose time is money...

To me cutting in before each socket just looks so untidy!

Yes and I fully agree about the Scotch Locks. Former cars I have owned had them fitted by previous owners. When I began to troubleshoot faults the Scotch Locks were usually found to be the problem. They were promptly replaced with soldered joints. Problem solved.

Kind regards
Lionel
Tombie
27th July 2018, 07:07 PM
Your Commo’ didn’t have a Trailer brake controller at some point?
Lionelgee
27th July 2018, 07:17 PM
Your Commo’ didn’t have a Trailer brake controller at some point?

Hello Tombie,

I think it is highly unlikely as the towbar is only rated to 750 kilograms. I asked a couple of local tow-bar and muffler fitters in Bundaberg about getting a heavy duty tow bar fitted back in March this year. They both separately claimed that it was illegal to fit heavy duty tow bars to VY Commodore Wagons because they were not strong enough.

A couple of months later I saw a VY Commodore wagon towing a very large caravan that was clearly rated greater than 750 kilograms. It seemed strange to me that a heavy duty tow bar could not be fitted to a wagon because they used to be considered a commercial vehicle. As in Australian made utes, panel vans and station wagons were identified as "commercial vehicles".

Kind regards
Lionel
LuckyLes
28th July 2018, 06:55 AM
Hi,
I'd pull the socket apart and check the wiring there first off. Could be a short between the connections in there. If you have tried different light systems and had the same result, then the cause is obviously in the car as you have determined. I have found, more than once, sockets wired incorrectly by a back yarder, who had then wired their trailer plug to suit.
LuckyLes