1984-1989 Corvette Delay Timer Testing.

There is a fuse our board… if you blow it it’s easy to check if you have a multi meter, but if you blew the fuse there is an issue with the car. Testing continuity from B to C if the fuse is good you’ll have continuity

If you blew the Mosfet… (Mosfet is the larger square item to the left of the green fuse) in the picture below. If this is burned you’ve cooked it and you have a really bad issue, I’ll elaborate below.

We updated the board design when we initially started reproducing the boards. We did this so that if the car has any issue it will blow the fuse and not damage the car or the board and thus preventing any other damage from being done to the car. Typically if there is a problem that took out the original board and the problem is still there! Replacing the board without fixing the issue only causes the same issue… the board blows!  This is exactly  why we fused it and to repair a blown fuse requires you to send us the board, the charge is 14.00 plus shipping.

Reported timers showing burns or disintegration from heat are not due to a flaw in the timer board.  The flaw that causes this issue can be found in the car in the form of a failed rectifier attached to the rear hatch release solenoid. All instances reported are directly related to the Coupe and Convertible cars and is caused by a malfunction in the rectifier used for the suppression of the voltage spike created by the rear hatch/deck lid release solenoid is activated.

The rear timer is sequenced with the rear hatch switch to prevent opening of the rear hatch while the car is in motion and to also turn on the interior lamp when activated. When the rectifier fails to stop the voltage, it spikes the board and causes what is termed thermal runaway.  A schematic has been posted on our website to help you understand the issue at this link.

http://repairs.willcoxcorvette.com/corvette-delay-lamp-timer-and-switch-schematic-1986/  <- updated link 08-11-2015

Now if the mosfet is cooked on the board (that is the large black square item on the board), you’ll need another board. We updated this in 2015 as well.  The new Mosfet, IRF540n is capable of taking 1000 volt spike, but even then this can be exceeded if the rectifier in the rear circuit is not working.

Willcox

 

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