First off the quit making the 780 in 1990. What do you mean brake relay? Brake light relay/integrity sensor? Need more information
Please go to this URL. I think 780 has the same relays and locations: http://www.davebarton.com/pdf/relay_87_700.pdf Igor.
Assuming you're referring to a Volvo VNL 780 truck, with the double bunk sleeper, 12'6".
You'd have to contact Volvo customer service for this. IIRC, there were a couple different options for the 730 and 780.
with a fridge
96 inches.
Try seaking seal
Volvo dealership. Have fun with that... if you've never taken off a Volvo starter, you could be in for a lot of excitement.
16"
15,000 to 18,000 lbs., depending on options.
You do not need any special tools to change out the auxiliary fan switch on a 1989 Volvo 780. The wrenches you normally use are sufficient.
On the right side of the throttle pedal
Curb weight for a 780 is typically between 18,000 - 19,000 lbs.