Transmission Retarder Lever location? Position?

[Stevie Wander]

Okay, I haven't driven my Wandelodge much. I need to get it over a small but intimidatingly steep hill and wan to use the transmission retarder.

I understand the retarder, when enabled, will kick in whenever the brake pedal is pressed (and note that engaging and disengaging the retarder should be done with your foot OFF the throttle) but that also there's a manual lever to adjust how much oomph it supplies. Only I'm not sure if it's the lever I'm thinking it is.

On a 4-speed Allison (HTB748), 1987 vintage, is the transmission retarder the black lever, under the dash but close to the shift selector? Slightly bigger than a cigarette lighter, one domed end piece, one cylindrical (or a bit tapered) shaft? I wish I had a pic.

If that's the right lever, is down the least resistance and up more resistance, or the other way around?

Cheers!