Definitely check the fuel pressure before replacing any parts.  You should have ~42 PSI at key on, idle, and WOT.

Get the interior of the throttle body clean with some carb cleaner spray.  Make sure to get all of the side passages and the butterfly edge clean.  Open the throttle to get good access.

Rather than throw parts blindly at it, download the MEFI 2 service manual and perform the tests in the book.  The PCM manual is fine if you can't find the one from Indmar.

You can also build or buy your own MEFI interface and read data from the ECM.

OK, some questions here for the experts:

1. If my trailer is sitting in my garage, fairly level, with nothing pulling on the tongue, the brakes should not be engaged at all, correct? So if I jack up one side and try to spin the wheel, it should spin, correct?

2. Using a "lockout" mechanism is to be able to back the trailer up without the brakes being applied if your vehicle does not have the right electrical connection to "tell" the trailer not to engage the brakes? If you have the 7-pin connector in place you should be good for that, right?

3. Another use of the lockout mechanism is to be able to disengage your brakes, if, while on the road, your brakes are engaging and heating up and you want to let them cool? Should not use long-term as it means no trailer brakes and your stopping distance would be longer, thus more dangerous?

4. If, while sitting level in the garage, you want to simulate the brakes being applied (compression at the tongue to engage surge brakes) you use a screwdriver in the slot on underside of tongue, pushing the piston back, so as to simulate the compression? While doing this, someone can try to spin the wheel and see if brakes engage.

Can we embed video here or only a link to a video?

Thanks

9 hours ago, uk_exile said:

Congrats getting it running. Well done.

No gauges and flickering lighting is probably bad connection. Most likely bad earth. Check the connections on the earth bar.

Why stop there?  Dive under the dash and check every connection you can find.

I would also check/replace all the idle air control valve and throttle position sensor. Does it run a little fast when going into gear?  I had a similar sounding issue and replacing these fixed it. Below is my favorite post to repost from @formulaben

I have bought out of state two times, never sold though.  For a sales transaction, I would handle it the same way whether local or not.  Certified check for full amount to be delivered at time boat is picked up, whether by a shipper or buyer.  Bill of sale would be emailed to buyer for signing and titles signed over at the time of pickup, would accompany boat on the trip or be overnighted depending on buyer's wish. 

I tried to purchase a boat that was 1000 miles away and I looked into delivery and picking it up over a long weekend.  Shipping would have cost about 3X what it would cost me to drive out and back, but ultimately decided that if I was buying that boat, I'd have had the trailer gone through wherever the boat was at including repack bearings, bleed brakes, and replace tires before making the trip. Turns out, the dealer couldn't locate the trailer (it was a racked boat) so I would have been buying a trailer and that added lead time just kind of made up my mind for me.  In the end, I bought boats 80 miles from my house and just stopped a couple times to make sure that the trailer wheels were not overheating or tires coming apart for that first trip home.