JasBass

Hi all. I have an 89 Z51 with the front and rear rad fan setup. Front fan (non engine side) runs fine and will operate normally when desired engine temp is reached. The rear fan (engine side) will run all the time, even when key is turned to ACC as well as while running.

I traced all the wiring to and from that relay and is as follows:
5 pin relay

85 (D, thin blue) looks to run in harness through firewall into interior
86 (F, thin blk/wht) ground to alt. bracket bolt

30 (E, red thick) from pos. battery terminal block drivers side
87a (C)- no connector, no terminal
87 (A, thick blk/red) runs to positive terminal of rear fan

negative pin from fan connector grounds to body through all black wire by power steering reservoir.

From an non professional eye, this looks to be correct. I would appreciate opinions. I know there is some involvement with the pressure switches on the AC lines, but wanted to see if this wiring was correct first. I have an electrical diagnostic book for a 91, but i've found enough subtle differences for me not to be able to track this down

WVZR-1

F - I'd expect DK GRN/WHT to ECM

Did you rewire this previously? A PO maybe and it's been this way since you bought it? Wired as you have it I'd expect the situation you have.

JasBass

PO had this wired up this way. I'm having to go back and clean up some of the previous work. Work was really well done, just don't understand why they did what they did. I've got the whole interior blown out down to the firewall and steering column, so it is a good time to work on wiring. I'm assuming the issue is with the ground on the alt, at minimum on the 85/86 side of things?

JasBass

Just gleaning from the 91 FSM, it looks like I need to track down the wire connection to the ECM for the 86 terminal (currently grounding to alt bracket). Looks like the AC pressure switches feed into the ECM and will charge the inductor to switch the circuit to ground.

JasBass

Just wanted to close out the post having found the problem. From my original post, pin 86 (F) was grounded to the alt bracket. I could see where the original grn/wht wire leaving the relay had been cut and a new piece spliced into it that was the alt ground. I opened up the harness and sure enough, the other half of the original grn/wht wire was sitting in the bundle. Traced it all the way back to the ECM. Used a waterproof 18 gauge connector and everything works as it should.
Next up, tracking down why the fuel pump runs non stop with the key in ACC. I suspect a similar grounding issue.

PatternDayTrader

Nice job.