Electrical Troubleshooting
 

Good weekend folks. first things first i have a 93 running an MS3Pro. i did a complete engine rebuild, turbo system upgrade, and chassis refresh on the car. i've gotten to the point where everything is back together except the interior. i got myself a fresh uncut harness from a clean car at the junkyard. here's my problem.

condition: key at "ACC" and all accessories (radio, cigarette lighter) are getting 12V

condition: key at "ON" MS3 lights 1 and 4 are illuminated, no prime to fuel pump, WHT-RED wire (ignition power) has 3.5V, circuit opening relay is not activating (no power on VIO wire {should be getting power from MS3}) therefore not actuating the relay and priming the fuel pump. LT-GRN wire at circuit opening relay has 3.5V

condition: key at "START" no changes to key at "ON"

ive swung tested a known working circuit opening relay and had the same results. where else should i be looking as far as relays or power supply? why isn't there enough juice flowing at "ON?" any help is appreciated.

EDIT: wiring harness is from a 92, and the only difference i've encountered was one of the plugs that feeds the chassis harness (to the fuel pump stuff) had to be repinned. continuity was checked on all wires to verify it was repinned correctly.

Just a shot in the dark, but clean the contacts in your ignition switch and put new grease in them.

completed. no change

Swapping the harness is a big touch. The low voltage on R/W is your smoking gun, stay on that. Confirm that R/W isn't shorted to ground, the tried a different relay with the same results step has derailed many. You can bypass the relay with a jumper to see if you get 12V on R/W. Download the wiring diagram and study it carefully.

will do. more to follow, making dinner and waiting for the temps outside to drop lol

also i already have 2 copies of the schematic. one in document protectors and one that's been abused for about two years 😹

confirmed i do nkt have short to ground. checked continuity from (WHT RED) to known hood ground and no beep. im about to do a few continuity checks on (WHT RED) and see what i come up with

Tail fuse powers TNS (main) relay coil

my bad, INJ fuse (contact)
engine fuse is coil

okay so im probing the (WHT RED) socket on the main relay socket and checking continuity to ground and im getting intermittent beeps so i must have a short to ground somewhere

Yeah, use resistance instead of continuity.

350.1 Ohms

Do you have 12V in the socket when the key is off (from the inj fuse)

0 VDC

In all 4 locations? If so, check INJ fuse

350 ohms isn't a dead short, but it's lower than it should be. Start removing fuses, see if the value changes. That'll tell you which leg is iffy.

350 is actually higher than what is on my car.

at the main relay socket i have 0 VDC on all 4 sockets in the off position. with key on i only have 3.5 at the (WHT RED) socket and 12V at the INJ socket

Ok, that is back drive most likely. Check that INJ fuse. You should have 12V in the location Joe P indicates in this thread

there was damage to the pin/wire but i fixed it and it runs!!!! thanks for your help man. i would have never looked there. lessons for next time lol.

Right on, we work for cats 😉