87 buick grand national power antenna went up, but won't go down.

Its most likely running because of a broken mast cable.
The ACC fuse powers the antenna. But it also powers the interior lights, door locks, etc..
May just want to go under the dash and find the connector and unplug it.
If you go for an aftermarket replacement mast, not all work.
The cable on that is most likely a smooth cabel with a J hook at the end. Most the aftermarkets have teeth and no hook.
Napa auto parts sells replacements that may work. When the antenna mast did the very same thing on my 89 Camaro I got a replacement from Corvette Central. Pricey for just a top section of the mast but just about all I could find.
Aftermarket antennas are fairly cheap and can work.

you don`t say where they keep breaking.if its around the bolts then you can use a thicker washer this might help.if the tracking system that the seat slides on then if there is room you might be able to weld a re-enforcing plate to the system where it cracks to stop it.

this can be caused by a failed Vehicle speed sensor or a mechanical fault in the transmission or the OD solenoid, run a test on the system and see if u have any fault codes. here is how to do a OBD1 GM fault code test, go to the link
http://www.extreme-check-engine-light-codes.com/GM%20OBD1%20Decoder.htm

Follow the upper rad hose to the intake, remove the hold down and the
steel fitting.

the Thermostat is behind that.

Make sure you Lube the new O ring in the fitting or you will have trouble getting it back in.

Symptoms Like this usually point to the Fuel pump.

Also these cars suffer from inferior wiring to the fuel pumps and a substantial Voltage drop is noted between the Fuel pump relay and the Pump harness.

The fix for this is a "Hotwire" Kit

Fuel pump kits with a Hotwire kit are available at numerous Buick performance Vendors but the best stuff in my opinion come from Racetronix,com

You should also change the Prom Chip in the ECM to a modern
Chip from Turbotweak.
This will improve driveability greatly.

HTH

i have a 1987 buick grandnational and put a new fuel pump in and the car will run about 5 min then just shut off

sign up at turbobuick.com (it's free)..I can almost guarantee that someone there nows how and will give you step by step instructions

coil is next on list.

First make sure you have no restrictions in exaust[converter] after you are sure of this check fuel pressure,this is critical to make sure you do not hurt pistons.

^ Turbo Cars have Lots of Vaccum, Where did you ever get this idea from. I have personally converted 10+ Turbo Buicks to Vac brakes.

Make sure the check valve is okay at the booster. but it does sound like you have a bad booster.
Also, did you change the brake pedal to a Vac brake pedal?
They are not interchangeable.

Also, you should not have drilled the plenum, you can get a vaccum block to replace the plastic one on the top of the plenum with a vac brake port.