Hi, got a question on wiring a Fuel Pump Relay on a TBI swap. Have read thru the sticky at the top, but it drifted off track. In going thru the search, it appears that different years used a different color scheme than that used by a later PCM. This is what I have came up with using a Bosch Relay, tell me if I'm on the right track. #30 - Grey wire from B12 on PCM, #86 - 12V switched, #87 - to pump, #87A - fuel pump prime? Hooks to what? #85 - Green w/white stripe from F6. The part that really throws me is the Grey wire ( B12 ), as its dinky for a main power wire for the f/pump, powering the relay. I have wiring diagrams for '88-'98 trucks, and a 16197427 PCM I've been using, but this fuel relay aint making sense. Thanks, Al

 

30 should hook to the battery (or the 12 volt switched)
87 to the pump
86 is probably the grey wire.
85 Ground

 

Would that mean the Dark Green w/stripe from F6 is not used then? Thanks, Al

 

dk grn/wht is the 12v call wire from the ECM. Without this, the relay will never engage

Gray is relay out to fuel pump
Orn is batt 12v input
Blk/wht is ground
Red is prime connector. Do not connect this, it is for testing purposes only. Once installed correctly, adding 12v to this connector will override the relay and force the pump to engage regardless of the ECM

GM used the same color combos and relay functions for most of the 90's, so as long as you've got all the colors, this is universal between vehicles. Older 3rd gens changed the pump wire from gry to tan/wht. Function is the same

Id post the pin assignements for a 3rd gen, but they dont apply to your truck or the truck PCM (different)

 

Thanks Guys. I'll be using a Howell TBI fuel pump, I guess I'm just having a hard time believing that thin, small Grey wire is where it gets its power from. Thanks, Al

 

Its 16ga and will carry more current than most people give it credit. Use a hotwire kit if you dont think its enough, just be sure to upgrade the intank wiring too

 

Thank you, Al