Classic/Antique Car Repair: 1986 gmc c15 pu, buic, shop teacher

Question
Hi there
I’m a 16-year-old kid and I recently purchased a 1986 gmc c15 that was originally a 6.2L diesel but has been changed to a 305 by the previous owner. I have rebuilt the truck and during the rebuild I noticed that one of the previous owners has replaced the 2 factory horns with one dinky Canadian tire unit. I decided it was time for an upgrade. I took the horns (4) out of a 93 Buic roadmaster and mounted them in the front of my truck behind the grill and added one more connector to each original power lead. I tested the new outfit and it worked well. But one day as I was moving it out of the shop my dog was in the way so I went to use the horn and all it gave me was a buzzing sound from underneath the dash. I determined that it was the relay that is attached to the steering column so I replaced the relay but it is doing the same thing. And I know it is the relay making the noise because if you touch the relay and activate the horn it vibrates. I have no idea what this could be or even where to start. I did check all the fuses and they are not blown. Any suggestions appreciated. Thanks Derek

Answer
Even though I am pushing 80, that is years not speed, I am used to 16 year olds. For 20 years of my work life I was a high school auto shop teacher. So, here we go. You say that the Buick yielded you 4 horns? That is a lot of electrical current to try to pass through one relay. If I was doing this job I would wire one relay for two horns and add a second relay for the other two. It sound simply that you over loaded the relay and it gave up the ghost. Now, do you have a volt meter? And do you know how to use it? If so check the voltage coming out of the relay. I'll bet that it is low and pulsing. In other words two horns per relay.