Plotting two graphs on the same figure

I want to add a line that represents the relationship between x and y to a strip chart, I've tried the following functions:
par(new=TRUE)
points(x,y)
lines(x,y)

but nothing works, I get the strip chart but line doesn't show up. Here is my function:

stripchart(hydfin$exp ~ hydfin$alt, vert = TRUE, pch = 1, method = "jitter", jit = 0.05, xlab = "Elevation", ylab = expression(paste(delta^{2}, "H")))
points(1:3, hydfin.M, pch = 16, cex = 1.5)
arrows(1:3, hydfin.M, 1:3, hydfin.M + hydfin.se, lwd = 1.5, angle = 90, length = 0.1)
arrows(1:3, hydfin.M, 1:3, hydfin.M - hydfin.se, lwd = 1.5, angle = 90, length = 0.1)
par(new=TRUE)
lines(hydfin$exp, hydfin$alt,type="l",col="red")