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
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