So I have my first FD electrical gremlin to troubleshoot, oh joy!

Problem: When signalling a left turn, the front turn signal doesn't flash at all, and both the rear turn signal & its dash indicator (left side) will hyper-flash (rapid flashing). The hazard flashers work fine on left & right sides, front & back, flashing at the normal rate, meaning that the front bulb is good.

I haven't had a chance to deep dive the FD wiring diagrams, but based on my FC experience this sounds like it could be a body CPU/flasher unit issue. Do FD CPU/flasher units have the same kind of old age issues that FC's did, like cold solder joints and disintegrating capacitors? Any tips on where to check first?

 

Rapid flashing could be as simple as a bad bulb

 

That was my first thought, but since all the same turn signal bulbs operate normally when I use the hazard flashers, it rules out dead bulbs.

 

Pete,

As Red94fd stated, that is an indication of a bad bulb. If the bulb is good then it could be an issue with the bulb contacting the lead inside the socket. Inspect the socket for corrosion then check the wires for proper contact by pushing them towards the bulb. My turn signals gave me trouble a few months back and this trick helped solve my problem.

Let us know what you find and how you fixed it, please.

 

^I tested that too, removed the "bulb harness" that connects the 2 bulbs to the 3 pin front/lighting harness plug and did a point-to-point resistance check on all the connections. There was a little corrosion on the bulb sockets that I cleaned up, and all continuity checks resulted in zero to a couple of ohms. Reinstalled and still the same problem.

 

When the hazards come on, it will cycle at a constant rate. It does not take into account any blown out bulbs. Did you test the suspect bulb while you had it removed? Either use a DMM to test the bulb or swap them from left to right. If the problem follows the suspect bulb to the right side then that's your problem.

You could verify the wiring from the socket to the Flasher CPU. The Flasher CPU connector is on the bottom of the Body CPU.

 

Yup, I tested the bulb for continuity which checks out fine, and all of the bulbs work as they should when the hazard flasher is switched on, so that rules out a bad bulb.

 

^Yep. I've run into this before, the turn signal circuit is more sensitive to a bad connection than the hazard circuit. I'd probably get 2 new front bulbs and check out the socket contacts.

If the flasher module sees the resistance in the circuit is wrong, it thinks the bulb is blown and does the hyper flash to let you know.

Dale

 

Pete,

Thanks for the added information. As I mentioned earlier, you could test the wiring to/from the Flasher CPU, then inspect the Flasher CPU for possible bad components and test the turn signal stalk switches.

 

Dale,

Thank you for those pearls of wisdom!

 

Sorry, I wrote my post when there was only 2 comments then walked away for a bit so I was missing some info.

It's possible it could be something with the flasher module itself. Could also be a bad connection there.

There may be a troubleshooting guide to this in the shop manual, worth going through if so.

Dale

 

I'll see if the FSM has a troubleshooting guide for this. Otherwise, next thing I'm going to try is just swapping bulbs side-to-side to see if the problem (a) persists as-is, or (b) problem switches sides. If (b) is the result, then I've got a bad bulb - putting a new bulb in should fix it. If it's (a), then either the bulb socket or a connection in that circuit/harness is adding just enough resistance to trigger the hyper flash and preventing that front bulb from lighting when turn signals are on

 

Also had a thought - I think the plugs for the turn signals are the same left and right. Swap the turn signals left and right and see if the problem stays with the bulb/harness or not. That would rule out the bulb and harness on each turn signal.

Dale

 

They are the same plugs (different wire colors though, duh!), so that's a great idea!

 

Dale & Pete,

You are correct, Sir! The turn signal lamp modules can be swapped. Both my FC and FD were afflicted with a similar symptom. My bulbs checked out but the housing intermittently worked. After knocking out some corrosion and some humidity, I used some electrical contact/connector cleaner inside the socket. I also pushed the contact pad towards the opening of the socket to ensure it made a positive contact with the bulb. Consequently, the problem has not returned on either FC or FD. *knock on wood*

One parting shot: Inspect the connectors on each turn signal module and on the harness side for corrosion or missing/bent pins. These connectors are very susceptible to water intrusion and the pins suffer the most damage from it.

 

Well go figure, I started this post describing it as a electrical gremlin, and true to form that's exactly how it's behaving - took the car for a spin after work today and the turn signal problem magically fixed itself! Completely normal operation of all turn signals, left/right, front & rear. Maybe my efforts in pulling the bulb harness & testing things may have done something useful, or appeased the rotary gods, but when I did a functional test last night before calling it quits, the problem remained.

Nice to know FD electrical systems are just as quirky and as much of a PITA as FCs are!

Let's see how long these turn signals stay "fixed"

 

Pete,

That's what I call FM...Flipping Magic (or insert your favorite expletive).

How much rain have you had lately? Is your FD garaged or exposed to the elements? Your problem could be from moisture build up. You could have dried out the connector and re-seated the socket.

 

No rain yesterday or on the days I drove it, with and without the problem occurring. The FD is garaged with my FC - my daily driver got kicked out when the FD showed up! Looking into putting in a 4 post lift so the daily ride can go back in the garage too.