Electrical 88 GT with 91 harness, no crank and low voltage on starter wire at ignition switch

[VSK2033]

Just got finished putting 95% of the car together and I went to test starter with fuel pump relay in to make sure everything was good and got nothing. Followed the no crank no start checklist and got the starter to work from touching the two large posts so I moved on and removed the connector off the small post and touch it to the post connected to the battery and the starter worked there too so I went inside the car and checked the white/purple wire at the switch and was only getting 4.7 volts while other terminals were getting 12.
My main issue is this is a wiring harness off of my old car that I put into this one and the previous person bypassed the clutch switch so I am not sure if maybe his hack job got messed up in the process of the install or if its something else but I am sorta at a lost currently as to why it is getting almost 1/3 the voltage it should be

 

[Mustang5L5]

How much of the wiring harness is from a 1991?

Generally 1988 and 1991 are not compatible. They are wired very differently so need to know how much of the harness you are using.

 

[VSK2033]

How much of the wiring harness is from a 1991?

Generally 1988 and 1991 are not compatible. They are wired very differently so need to know how much of the harness you are using.

All the wiring in the car is from the 1991 car, there's no wiring left in the car from 1988

 

[Mustang5L5]

Do you have 12v on the yellow wires?

The ignition switches on these cars are know. For not being so robust. Do you have a other one to try out?

 

[VSK2033]

Do you have 12v on the yellow wires?

The ignition switches on these cars are know. For not being so robust. Do you have a other one to try out?

Thats the worst part I tracked it back to the switch after doing the tests so I did that first and tried two used switches so I cant imagine both are bad when I know that one used to work, my current idea is that it has to do something with the clutch switch since that white/pink wire is only getting 4.7 volts while other terminals on the ignition switch are getting 12, Im not entirely sure what is limiting the voltage but it has to be something in that circuit I believe and that would make sense why it is not starting from the key

 

[Mustang5L5]

How did he bypass the clutch switch? Depending on what they used, it could lower the voltage if there is an increase in resistance.

You need to remove the bypass and then measure voltage on the red/blue wire. If you don’t have it there, crawl under the car, unplug the reverse light harness (where the NSS jumper is on the 5-spd cars) and measure the voltage on the red/blue wire there. If you still don’t have it, you either have a damaged white/pink wire of the ignition switch just isn’t outputting the proper voltage for some reason.

You need to isolate the circuit and work backwards to the source to rule out potential causes of the voltage drop.


Usually, a 5amp blade fuse is all that’s needed to bypass the clutch switch, however you may want to consider just making it functional.