New here. Wiring problem

[T.Huck]

Hi!
I'm T.Huck, and I'm in West Texas. I have owned a '65 GMC 3/4 ton flatbed truck since the early 90's. It had the old V6 motor, and my daughter blew it up in 2001. I put a 350 V8 in it, from a '69 Chevelle, that had around 100.000 miles on it. My son then started driving it and had it for a few years. he then threw a piston rod thru the oil pan. The old truck sat at my ex-father in law's farm for about 10 years until I got it a few months ago and started making a rat rod out of it. I had another 350 from a '71 Corvette, and have installed it in the truck and am about ready to start it up. I have one problem.

I am doing this on a shoestring budget, and have done pretty good so far, but have spent a bit of change on a couple things, such as a generator to alternator conversion, and some wiring. I ordered an engine harness from a classic truck dealer, and made a mistake and ordered the one for a Chevy instead of a GMC. The harness plugs into a socket on the drivers side firewall goes along the fender, to the front radiator grille area. there is a plug in to the headlights, and a plug for the horn relay, and in this is my problem. The harness has a two wire plug that goes to the relay, and a seperate thick red wire that has a spade connector that goes onto a screw post, and the existing horn relay only has a three wire plug. I purchased a new horn relay for a Chevrolet truck, thinking that I would just use it, but it is quite different in that it has two screw terminals. I have looked up diagrams on line and just became confused, as they all reference a voltage regulator.

Has anyone here had the same trouble, or know haw to deal with this issue? I do not wish to invest in another harness if I don't have to.....


Thanks!

[ray_mcavoy]

Welcome!

The 2 screw terminals on the Chevy horn relay serve as a buss bar or junction block that is used to tie all of the main feed wires together.

Your new harness should have 2 of those thick red wires with spade terminals ... one is the main power feed into the truck cab and the other is the output from the alternator. Both of them should be connected to the screw terminals on the horn relay. It doesn't matter which screw since they're electrically connected.

You will also need to run a similar gauge (typically 12ga) wire from the positive battery terminal, across the radiator support, and connect it to one of those screw terminals on the horn relay. Although not factory, it is a good idea to add a fusible link to the battery end of this wire ... use a 16ga fusible link to protect a 12ga wire.

Finally, the voltage regulator's voltage sensing wire also attaches to one of the horn relay screw terminals. For the factory external regulator, this is 16ga red wire going to the regulator's #3 terminal. For a newer 10SI or 12SI internally regulated alternator, this would be a wire connecting from the alternator's #2 terminal to the horn relay. Some installations take a shortcut on this and simply loop the wire from the #2 terminal over to the alternator's output stud (it works in most cases but doesn't offer remote voltage sensing capability).

[T.Huck]

Thanks for the welcome, and thanks for the info! I wont be working on it again until next Tuesday, but will check all this out. Believe me, if I have any more questions I'll post right away!

T.Huck