OK, here's the joint transcription from Dale, Gene, Joe, and Sourdough:

LITTLE RED CABOOSE BEHIND THE TRAIN
Paul Warmack and his Gully Jumpers

I am growing old and weary
And my sight is getting dim
I have laid my links and pins away to rust
And the only friend that's left to me
In this wide world to stand
Is the Little Red Caboose Behind The Train.

CHORUS
Oh, I'm growing old and feeble now
And my sight is getting dim
And I cannot see those signals anymore
I can hear those whistles blowing
And I know I'll soon be going
To a better home I know that, far away.

There are young ones coming on
It is time for me to go
They'll be pestered with the rain, the sleet and snow
And they'll find a heap of trouble
When those hills they have to double
With the Little Red Caboose Behind The Train.

CHORUS
^^

And the notes from Dale:

The Little Red Caboose Behind The Train/Paul Warmack and his Gully Jumpers, recorded Nashville, TN 10/1/28 From The Railroad In Folksong, RCA Victor Vintage Series 532, 1966.

From the notes (not much on this song) The Grand Ole Opry, in its first decade, featured a handful of Tennessee String Bands like Paul Warmack's Gully Jumpers. The Little Red Caboose Behind The Train is a folk parody of Will Hay's minstrel classic "The Little Log Cabin In The Lane." Railroaders delighted in caboose ditties which evoked the warmth of a trainman's home and the spirit of his final parting. ARCHIE GREEN

"Links and pins," the predecessors of couplers, were used to join train cars together - so those words seem to me to be the correct interpretation.
-Joe Offer-