Messages

Thanks Phillip!
I've been registered for many years and finally read a post to which I could respond with some useful information.

Vic Yarberry at Cougars Unlimited might be able to...

Depending on what has failed, the OEM circuit boards may be able to be repaired.
Many times the copper on the circuit board is corroded beyond repair by water entering the rear quarter.

If the board is intact, the typical failure points are:

1. Glass diodes - the larger germanium diodes fail open - check with a DVM.
   These diodes can be replaced with a 1N34A diode.
2. Power SCRs - these transistors fail open, shorted, or with degraded specs.
   These SCRs can be replaced with a C106B1 (higher voltage).
   Use parts with a TO-202 case, some replacements use a TO-220 case, which does not fit on the heatsink.
3. 8-pin Hybrid module circuit - the internal transistors can fail.
   A replacement part is not available - transplant a known good part.
4. Relays - found only on later service parts; the internal contact arm breaks off inside the OEM Littelfuse relays.
   Replace with a Ford horn relay, C4AZ-13853-A.
5. Bad connectors
   Replacement connector pairs are available from Cougars Unlimited.

Note: the internal circuit diagram shown in the factory wiring diagrams is incorrect.
Ford used two different versions with some minor differences.

Generally, the amount of labor time and difficulty obtaining the components, may make these repairs cost ineffective. Also, modern high-power "Plasma" LEDs cannot be used with the OEM boards. The latest generation replacement boards eliminate the voltage drop (and bulb brightness loss) inherent with the SCR transistor-based OEM sequencer.

LMK if you have any questions.

Vic Yarberry
Cougars Unlimited LLC

The addition of the four relays to the sequential controller boards was a production change as of 1/1/70 for Cougars and Thunderbirds. The change was an attempt to make the rear lights brighter to meet 1970 Federal lighting standards. The relays eliminated the ~ 1V voltage drop across the SCR transistors used in the original sequential boards thus theoretically making the lights brighter. The under dash turn signal flasher can was changed to a green D0WY-13350-C at the same time to accommodate the increased current draw and maintain the correct flashing rate.

Since all the 1969-70 Shelby Mustangs were built prior to 1/1/70, none came with a sequential controller with relays. However, it was the service part available from Ford. Unfortunately, the relays are not reliable. The contact spring arm on these relays eventually work hardens and breaks off. When the arm breaks off, it either shorts the light on or renders the relay ineffective.

The current reproduction sequential controller boards do not use relays and do not have a provision for adding them to improve long term reliability.

Vic Yarberry
Cougars Unlimited LLC
www.cougarsunlimited.net