Electrical 1986 Mustang GT 5.0 Starting Issues


New Member
Apr 29, 2019
River Falls, WI
Hi All,

I am new to the form and recently acquired an 1986 Mustang GT 5.0. Before I became the owner of the car, I did test drive it, but the previous owner told me he bump started it.

I assumed it needed a new starter. I replaced the starter, the starter solenoid, battery, and postie & negative battery cables. At this time i still can not get the vehicle to start.

I have jumped the starter solenoid and can only get a single crank/click out of it. I did notice a spark coming off a wire (possibly engine temp gauge wire??) that starts at the engine block and goes through the firewall under the dash somewhere.

I can post pictures as visuals are needed.

I am baffled why i cant get the car to start when putting 12 volts to the starter solenoid. Does anyone have any recommendations or trouble shooting tips?

Just an FYI this car appears to have had many owners and butchered quiet a bit, so it is very possible something is wired incorrectly.

Thanks in advance for any assistance,

  • Sponsors(?)

General karthief

wonder how much it would cost to ship you a pair
Mod Dude
Aug 25, 2016
polk county florida


StangNet's favorite TOOL
SN Certified Technician
Mar 10, 2000
Dublin GA
No Crank checklist for 5.0 Mustangs

Revised 24-Oct-2013 to update voltage drop figures.

No crank, slow crank and stuck starter solenoid problems have the same root causes – low battery voltage and poor connections. For that reason, they are grouped together.
Use the same initial group of tests to find the root cause of slow crank, no crank and stuck solenoid problems.

Since some of the tests will bypass the safety interlocks, make sure that the car is in neutral and the parking brake is set. Becoming a pancake isn’t part of the repair process…

1.) Will the car start if it is jumped? Then clean battery terminals and check battery for low charge and dead cells. A good battery will measure 12-13 volts at full charge with the ignition switch in the Run position but without the engine running.
A voltmeter placed across the battery terminals should show a minimum of 9.5-10 volts when the ignition switch is turned to the Start position and the starter engages or tries to engage. Less than this will result in a clicking solenoid, or slow cranking (if it cranks at all) or a starter solenoid that sticks and welds the contacts together.

Most auto parts stores will check your battery for free. It does not have to be installed in the car to have it checked; you can carry it with you to the auto parts store.

The battery posts and inside of the battery post terminals should be scraped clean with a knife or battery post cleaner tool. This little trick will fix a surprising number of no start problems.

The clamp on with 2 bolts battery terminal ends are a known problem causer. Any place you see green on a copper wire is corrosion. Corrosion gets in the clamped joint and works its way up the wire under the insulation. Corroded connections do not conduct electricity well. Avoid them like the plague...

If the starter solenoid welds the contacts, then the starter will attempt to run anytime there is power in the battery. The cables and solenoid will get very hot, and may even start smoking. The temporary fix for a welded starter solenoid is to disconnect the battery and smack the back of the solenoid housing a sharp blow with a hammer. This may cause the contacts to unstick and work normally for a while.

A voltmeter is handy if you are familiar with how to use it to find bad connections. Measure the voltage drop across a connection while trying to start the car: more than .25 volts across a connection indicates a problem. The voltage drop tests need to be done while cranking the engine. It's the current flowing through a connection or wire that causes the voltage drop.

See http://assets.fluke.com/appnotes/automotive/beatbook.pdf for help for help troubleshooting voltage drops across connections and components. .

Voltage drops should not exceed the following:
200 mV Wire or cable
300 mV Switch or solenoid
100 mV Ground
0.0V Connections
A voltage drop lower that spec is always acceptable.

2.) Check the battery to engine block ground down near the oil filter, and the ground behind the engine to the firewall. All grounds should be clean and shiny. Use some sandpaper to clean them up.

3.) Jump the big terminals on the starter solenoid next to the battery with a screwdriver - watch out for the sparks! If the engine cranks, the starter and power wiring is good. The starter relay is also known as a starter solenoid.

The rest of the tech note only concerns no crank problems. If your problem was a stuck solenoid, go back to step 1.

4.) Then pull the small push on connector (small red/blue wire) off the starter solenoid (Looks like it is stuck on a screw). Then jump between the screw and the terminal that is connected to the battery. If it cranks, the relay is good and your problem is in the rest of the circuit.

5.) Remember to check the ignition switch, neutral safety switch on auto trans and the clutch safety switch on manual trans cars. If they are good, then you have wiring problems.

Typical start circuit...
Diagram courtesy of Tmoss & Stang&2birds

6.) Pull the starter and take it to AutoZone or Pep Boys and have them test it. Starter fails test, then replace it. If you got this far, the starter is probably bad.

Starter solenoid wiring for 86-91 Mustang

Starter solenoid wiring 92-93 Mustang or earlier Mustang with upgraded high torque mini starter.

Electrical checks for the switches and starter solenoid

Remove the small red/blue wire from the starter solenoid. Use a screwdriver to bridge the connection from the battery positive connection on the starter solenoid to the small screw where the red/blue wire was connected. The starter should crank the engine. If it does not, the starter solenoid is defective or the battery lacks sufficient charge to crank the engine.

If the starter does crank the engine, the problem is in the clutch safety circuit (5 speed) or Neutral Sense Switch (auto trans) or ignition switch.

See the Typical start circuit diagram above for wiring information for troubleshooting.

You will need a voltmeter or test lamp for the rest of the checks. Connect one lead of the voltmeter or test lamp to ground. The other lead will connect to the item under test.
Look for 12 volts on the white/pink wire when the ignition switch is turned to the Start position. Check the ignition switch first.
No 12 volts, replace the ignition switch.

The next step will require you to push the clutch pedal to the floor (5 speed) or put the transmission in neutral (auto trans) while the ignition switch is turned to the Start position.
Good 12 volts, check the clutch safety switch (5 speed) or Neutral Sense Switch (auto trans) for good 12 volts on both sides of the switches. No 12 volts on both sides of the switch and the switches are defective or out of adjustment. Check the wiring for bad connections while you are at it.


New Member
Apr 29, 2019
River Falls, WI
*Update - 4/30/2019

I appreciate at everyone's help. It turns out it was a bad ground connection at the firewall. It starts perfectly now.

Thanks again for all the assistance,

Thread starter Similar threads Forum Replies Date
B [Project Car] 1986 5.0 V8 Foxbody Mustang Starting Issue Fox 5.0 Mustang Tech 8
N 1986 Mustang Gt Not Cranking Over Fox 5.0 Mustang Tech 12
O Engine 1986 Mustang Only Starts Cold, Suggestions? Fox 5.0 Mustang Tech 11
jrichker Help me create the "Surging Idle Checklist" Fox 5.0 Mustang Tech 560
I 1986 Ford Mustang Starting Problems SN95 V6 Mustang Tech 2
S Did all mustangs get 8.8 starting in 1986? Fox 5.0 Mustang Tech 2
Nick Bos Can I fit a 1979-1986 C4 Nuetral Safety Switch to my 1970 mustang C4? 1965 - 1973 Classic Mustangs -General/Talk- 1
S 351 w in 1986 mustang help 1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk- 2
Driver460sz Electrical 1986 (5-spd) mustang reverse lights not working. Fox 5.0 Mustang Tech 10
F 1986 Mustang GT Interior questions 1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk- 21
1984Convert WTB/Trade 1985-1986 Mustang rear bumper cover Fox Body Mustangs For Sale (1979-93) 0
UsernameRequiredFox WTB/Trade 1986 Mustang GT! WTB! Fox Body Mustangs For Sale (1979-93) 0
S Exhaust 1986 Mustang - Exhaust setup Fox 5.0 Mustang Tech 14
W 1986 Mustang GT Convertible Fox 5.0 Mustang Tech 5
J 1986 Mustang LX Convertable Wheels 1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk- 3
G (Help) Car Wont Run : Mass Air Conversion 1986 Mustang Issues Fox 5.0 Mustang Tech 7
A For Sale 1984-1986 Ford Mustang SVO Turbo Gauge Cluster - VGC Interior Exterior Parts 1
P 1986 Mustang Convertible Parts 1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk- 2
M 5.0 Swapping A 1986 3.8 Mustang Need Advice! 1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk- 0
Russ77 Expired 1986 Svo Mustang Fox Body Mustangs For Sale (1979-93) 0
V 1986 Mustang 5.0 Running Problems Fox 5.0 Mustang Tech 16
bluelx347 Expired 1986-93 Ford Mustang Sve 130 Amp 3g Alternator Upgrade With Braket - $125 Engine and Power Adder 0
S Expired 1986 Mustang Gt Convertible Fox Body Mustangs For Sale (1979-93) 2
Davedacarpainter 1986 Mustang Production Line 1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk- 10
A My 1986 Mustang Lx Coupe The Welcome Wagon 5
MRaburn SOLD 1986 Mustang Gt - 39k Original Miles - Survivor Fox Body Mustangs For Sale (1979-93) 13
E 1986 Mustang Idle Tough Idle Problem Fox 5.0 Mustang Tech 2
tacomatrx450f Expired 1986 Mustang Gt Convertible Fox Body Mustangs For Sale (1979-93) 0
R 1986 Mustang Power Window Switch Layout Fox 5.0 Mustang Tech 1
R Expired 1986 Foxbody Mustang 302 5.0 Custom - $6000 Fox Body Mustangs For Sale (1979-93) 0
T Expired 1986 Ford Mustang V6 In Excellent Condition Fox Body Mustangs For Sale (1979-93) 0
tacomatrx450f Gt40 Heads On Stock 1986 Mustang Fox 5.0 Mustang Tech 2
B SOLD 1986 Ford Mustang G.T. Convertible For Sale (Danville, CA) Fox Body Mustangs For Sale (1979-93) 0
bgjohnson SOLD 1986 Mustang SVO. 25k miles, 2nd owner. Fox Body Mustangs For Sale (1979-93) 9
M 1986 mustang with different motor? Classic Mustang Specific Tech 2
TurboDude Back Into Mustang Iis Since 1986 The Welcome Wagon 0
E Need To Sell My New 1986-1993 5.0l Mustang "renegade/efi" Paxton Supercharger 1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk- 2
C Expired 1986 Mustang Gt T-top 42k Miles Fox Body Mustangs For Sale (1979-93) 4
B 1986 Mustang Gt Convertible - 1 Owner - Red/gray - Michigan Fox Body Mustangs For Sale (1979-93) 0
B 1986 Ford Mustang G.t. Convertible Fox Body Mustangs For Sale (1979-93) 2
keithnra 1986 ford mustang coupe for sale Fox Body Mustangs For Sale (1979-93) 2
79'293stang 1986 Mustang SVO Fox Body Mustangs For Sale (1979-93) 6
J Diagnose Fuel Pump 1986 LK Mustang 3.8 Fox 5.0 Mustang Tech 24
C *F/S*1984-1986 Mustang SVO & 1993 Cobra Tail Lights w/ BLACK STRIPES Interior Exterior Parts 0
Blown331LX 1986 Mustang GT Convertible 5spd - 90k orig miles / Stock - Needs Work but easy resto Fox Body Mustangs For Sale (1979-93) 0
palmaceae 1986 Mustang GT Convertible Fox Body Mustangs For Sale (1979-93) 1
gxnos 1986 Mustang GT, Crimson Red, 500+ hp Daily Driver, 70mm Turbo Fox Body Mustangs For Sale (1979-93) 12
E 1986 Mustang GT F/S.... Fox Body Mustangs For Sale (1979-93) 4
A 1986 Mustang GT Fox Body Mustangs For Sale (1979-93) 0
Mystic1350 1986 Ford Mustang GT 1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk- 6
Similar threads