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· Registered
1988, Bronco, 5.0L EFI, manual 5 speed.
26 Posts
Discussion Starter · #1 ·
Recently purchased an 1988 Bronco XLT. 302 with a manual transmission 5sp OD/manual locking hubs. Not sure which transmission it is. I just put the 302 in the rig but need help with the wiring(factory 302 was seized). I found the diagram for a 1990 on here but haven't seen anything for the 1988. I believe the wires and colors are similar. My issue is the previous owner installed a push button to bypass the start position on the ignition. I replaced all the steering column components for the ignition. I haven't checked or replaced the clutch pedal switch as of yet. As of now the ignition turns everything on but will not bump the starter. The bypass button is essentially a jumper wire from the battery to the starter relay. Any ideas of what other circuits would cause a no start from the switch?(I have not fired the engine off, tackling one small piece at a time) I do have the red/Light blue wire in the 1990 diagram on the solenoid. If the manuals are all the same then I will continue digging through the 1990 but if they are not an 88 manual might help me out.

· Registered
1988, Bronco, 5.0L EFI, manual 5 speed.
26 Posts
Discussion Starter · #4 ·
I only recall a transmission position switch in the cranking loop circuit. I don't think the computer has anything to do with it.

Do you have power at the R/LB wire at the relay when the key is in start position? Have you attempted to bridge battery positive to the R/LB wire stud on the relay to verify the relay works? Have you bridged batter power to the starter cable to verify the starter works?
The start button that is installed(not by me) is bridging the power between the battery and the relay currently. One could probably call me picky that I want the key to work like its suppose to. I probably need to check to clutch interlock switch to make sure it is good. I should be able to bypass it temporarily to see if it is working or not. If that isn't it then I'll be back at square one. The diagram above is definitely a less complicated version of the one in the 1990 manual but I was able to decipher it. I would imagine there are some other electrical issues on the truck that I haven't found yet but I will get there with time.

· Registered
1988, Bronco, 5.0L EFI, manual 5 speed.
26 Posts
Discussion Starter · #5 ·
Yo dabernathy8181,
View attachment 174664
I need to roll now, will be back tomorrow.

Your 88 5.0 most likely has the Mazda M50D (5-Speed) manual transmission
View attachment 174662

Here's the 1988 Ford Bronco & Truck Service Manuals by Larry J via Kingfish999 in Google Drive @ 1988 Ford Truck Service Manuals (Thank you Larry Jorgensen) - Google Drive

1988 Bronco Dealer Brochure @

Haynes Red Manual for 80-95 Bronco & F Series @ Hanes guide 80-96 bko f series.pdf by BroncMom

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Thanks for the info, My issue is in the Interlock switch, It looks like someone tried to jump between the red/light blue wires on the back of the plug but it didn't work, I was able to take the plug off the switch and jump the connection side and the switch works, I'll have to go through the diagrams to see what the other wires do. THe switch wasnt attached to anything which is the first issue, so I'll have to find a complete sitch and go from there.

· Registered
1988, Bronco, 5.0L EFI, manual 5 speed.
26 Posts
Discussion Starter · #7 · (Edited)
Yo d,
Forgot to ask you about other items that were "touched" by previous owner or sho, such as ignition switch, etc.
Some more info for your 88 5.0
"Ignition switch:
1. Disconnect the battery ground cable.
2. Remove steering column shroud and lower the steering column. Refer to Steering Column: Service and Repair: Removal/Installation.
3. Disconnect the switch wiring at the multiple plug.
4. Remove the two nuts that retain the switch to the steering column.
5. LIFT the switch VERTICALLY UPWARD to disengage the actuator rod from the switch and remove switch.

1. When installing the ignition switch, both the locking mechanism at the top of the column and the switch itself must be in LOCK position for correct adjustment.
To hold the mechanical parts of the column in LOCK position, move the shift lever into PARK (with automatic transmissions) or REVERSE (with manual transmissions), turn the key to LOCK position, and remove the key. New replacement switches, when received, are already pinned in LOCK position by a metal shipping pin inserted in a locking hole on the side of the switch.
2. Engage the actuator rod in the switch. Must be inserted in the slot of the sliding, black carrier.
3. Position the switch on the column and install the retaining nuts, but do not tighten them.
4. Move the switch UP and DOWN along the column to locate the mid-position of rod lash. Tighten the two ignition switch retaining nuts (TOP NUT FIRST to minimize rod binding) to 4.51-7.34 N.m(40-65 in-lb).
5. Remove the lockpin. Connect the battery cable, and check for proper start in PARK or NEUTRAL.
Also, ensure the start circuit cannot be actuated in the DRIVE and REVERSE position and that the engine will shut off in either DRIVE, REVERSE or NEUTRAL. If the engine will not shut off in the above positions then the switch is NOT adjusted properly.
The switch will have to be re-adjusted. Refer to Ignition Switch: Adjustments.
6. Raise the steering column into position at instrument panel. Refer to Steering Column: Service and Repair: Removal/Installation.
7. Confirm that accessories are deactivated with ignition switch in OFF position, and that accessories are operable with switch in RUN position.
ROTATE the ignition key back and forth to either side of lock, until a 1.98 mm (5/64-inch) drill bit can be inserted through the lockpin hole as far as possible (minimum 9.5mm (3/8 inch) ). The lock pin hole is located on the right of the switch next to the steering column tube.
2. Loosen the two ignition switch mounting nuts.
3. Turn the ignition to LOCK (feel for detent) and remove the ignition key.
4. Move the switch up and down along the column to locate the mid-position of rod lash. Tighten the two ignition switch mounting nuts (TOP NUT FIRST to minimize rod binding) to 4.51-7.34 N.m (40-65 in-lb).
5. Remove the drill bit from the ignition switch lockpin hole.
6. Plug in electrical connector and operate the lock cylinder to ensure the switch is positioned properly.
7. Confirm that all accessories are deactivated with ignition switch in OFF position, and that all accessories are operable in RUN position."
View attachment 174721
View attachment 174723
View attachment 174724
View attachment 174725
Issue resolved. The clutch interlock switch was removed and the previous owner tried to jump the start wires but appeared to be unsuccessful and added the push button to start. I reinstalled the interlock switch and it functions as should. I think part of the reasoning for removal was the firewall flex which I have a kit from the bronco graveyard to install.
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