I was having some intermittent problems with the carburetor cooling fan and it just stopped working. after hrs of troubleshooting I discovered it was the computer by grounding the fan power M4 relay.
Here is a retrofitted timer relay setup to replace the computer with a modern timer that functions very similar to the original computer. (Pictures and info below)
The labeled wires in the picture show the colors to connect to in the circuit. The way the fan powers on is the computer closes to ground from the thermistor. For this to work you must have that thermistor on the block near exhaust always grounded. Most people already have it grounded due to the wire melting.
The timer was bought from Amazon. It has 7 programs that do different functions. I am running program 2 on the timer relay. Set to 1200 seconds (20 min). The wiring config allows the thermistor ground to pass through the computer for 20 min to the M4 relay. That relay kicks on and powers the fan. The timer and relay is triggered by connecting the labeled ground switch wire to a ground in the dash. Push button style switch.
So I turn off the ignition and push the switch to start the 20 min fan run. Really only need it when it’s over 80 degrees out.
Timer Relay: Time Delay Relay, DROK Timer Delay Controller Module DC 5V 12V 24V Delay-Off Cycle Timer 0.01s-9999mins Adjustable Trigger Delay Switch Control Relay Board with LCD Display Support Micro USB 5V Input https://a.co/d/guih4Aq
Ignore the programming on the computer below. I was troubleshooting. Run it on P2 for 1200 secs. Each time you hit the switch to ground the timer starts over. This relay came with good instructions.
Also, there are other timer relays with more functions that you could use the ignition off to trigger the timer start. I liked this one because I can control when it runs by a switch.
Here is a retrofitted timer relay setup to replace the computer with a modern timer that functions very similar to the original computer. (Pictures and info below)
The labeled wires in the picture show the colors to connect to in the circuit. The way the fan powers on is the computer closes to ground from the thermistor. For this to work you must have that thermistor on the block near exhaust always grounded. Most people already have it grounded due to the wire melting.
The timer was bought from Amazon. It has 7 programs that do different functions. I am running program 2 on the timer relay. Set to 1200 seconds (20 min). The wiring config allows the thermistor ground to pass through the computer for 20 min to the M4 relay. That relay kicks on and powers the fan. The timer and relay is triggered by connecting the labeled ground switch wire to a ground in the dash. Push button style switch.
So I turn off the ignition and push the switch to start the 20 min fan run. Really only need it when it’s over 80 degrees out.
Timer Relay: Time Delay Relay, DROK Timer Delay Controller Module DC 5V 12V 24V Delay-Off Cycle Timer 0.01s-9999mins Adjustable Trigger Delay Switch Control Relay Board with LCD Display Support Micro USB 5V Input https://a.co/d/guih4Aq
Ignore the programming on the computer below. I was troubleshooting. Run it on P2 for 1200 secs. Each time you hit the switch to ground the timer starts over. This relay came with good instructions.
Also, there are other timer relays with more functions that you could use the ignition off to trigger the timer start. I liked this one because I can control when it runs by a switch.
