Jimmy: I notice you have an 88 coach, does it have the DDEC system or is the engine controlled through a mechanical governor. Given the symptoms I would suspect a mechanical governor but you need to confirm this before we proceed. THe two types of engines have different control circuits for the Jake.
In either case I suggest you go to the Jacobs Engine Brake website and download the manual for the system. Here is the link to the "mechanical" engine:
http://www.jacobsvehiclesystems.com/...dfs/003879.pdf
If this is your engine you will want the section titled "Control System Installation".
Now, a a quick review of how the system operates. On my engine with a single stage of engine braking electric power is supplied to the "Jake Brake" switch on the dash. When that switch is on power then flows to the "buffer switch" on the governor. The buffer switch passes power only when the engine is above idle speed and the governor is calling for no fuel (engine is coasting and being driven by the vehicle rather than driving the vehicle). When the "buffer switch" closes it passes power to a solenoid under the valve cover for each bank of cylinders. Energizing that solenoid valve changes an oil pressure at the exhaust valves that opens them just as the piston is near the top but not in a position to hit the exhaust valves. The high pressure in the cylinder is released through the exhaust instead of pushing the piston down so the engine essentially becomes a big air compressor absorbing power from the drive wheels and slowing the vehicle.
If the engine has multiple stages the power flow starts at the "buffer switch", goes the the stage selection switch on the dash and then to the solenoid valves under the valve covers. There will be one solenoid valve for each stage.
The setting of the buffer switch is critical because if it comes on too soon the engine will be trying to brake and provide power at the same time - the kind of thing that could cause damage. If it comes on too late no braking will occur. When adjusting the buffer switch you are adjusting its position relative to a part inside the governor. Do not adjust the switch or its mounting on the bracket as this will really mess things up. The other advice relative to adjustments is to take it slow with 1/8 turn adjustments. On mine I went from having a rough engine with banging at higher engine speeds to operating properly 1/4 turn out. Following the manual cautiously will be just fine if you have good mechanical skills.