...Where is it? Sorry for the stupid question, but, I have very little idea...1986 Merkur. Is it the boost control selenoid? I hope not, because I've pretty much gutted the wiring for it so far and I don't want to rebuild the loom.

 

Put in adjustable control or diy. Do search worded. DIY boost control. Darn forum won't let me do a link.

 

Like he said you can build one. I've built about 10 of them for customer/friends. I just finished one actually for my friends '85.5 svo a few days ago.
They cost about $15 to build & you need a drill/tap. You may need a bit the size of the ball to grind out some material, most times the ball doesn't like to fit well.
I build all of mine with a drill press & the same tap. I use two different bits. They're pretty cheap though.

The only real trouble you may have when building one is springs. Some springs have different rates so you can't go by just size alone. Thats easy to fix though, get a spring make a run in 2nd gear 1/4 - 1/2 throttle & to test it. If it overboosts, cut the spring a little shorter & keep repeating until you get it the right size.

Better to diy though, No point in wasting $50 for a boost controller. I did that like 4 years ago for my first turbo project, took it apart & couldn't help but notice that every single part to it they had at the local hardware store other than the ****.