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Engine fan power. 73 1608.

Posted: Sat Jul 27, 2019 8:32 am
by Funcar
Yes I know that there is a lot of information on the engine fan and how it works. However I would ask for some advice on getting it running.

Initially when I got the car very little of the electrical was working but managed to clean grounds etc. and got most things working. To get the engine fan working I jumped the 2 leads to the thermal switch so it was always on with the ignition switch. I did put in a new thermal switch but still couldn't get the fan come on at temp over 90 so just jumped it so I could enjoy driving.

Now what has happened is while driving the fan has stopped working and next thing I know the car dies as also the electric fuel pump stops working. This happens when the temp gage gets over 90. Sometimes the 16 amp fuse blows and sometimes not. When the car cools down the fuel pump and horn work but I don"t get power to the engine fan.

Here are some pictures of my wiring. I would like to know how to trace the power wire to the fan connector.


Connecting wire from harness to fan.


ground for engine fan


wiring in engine bay drivers side in front of relays.


Wiring you see in front of drivers seat. You can see ignition on the right


Fuse box


wiring behind fuse box. you can see hood latch.


wiring above brake and clutch pedal.


Re: Engine fan power. 73 1608.

Posted: Sat Jul 27, 2019 11:34 am
by spider2081
I'm pretty sure you have a coolant fan relay in the circuit that you have not mentioned. The relay's coil is powered by the ignition switch when the switch is in the run & start positions. This closes contacts 30 which has power all the time and contact 87 that brings power to the coolant fan motor. The temperature switch in the radiator will supply the ground when the temperature is above 190.

Fuse 10 (i believe that is closest to the drivers door) unfused terminal (top) is where the relay coil terminal 85 gets its power =12 volts.
I don't know for sure but I think fuse 9 is internally jumped to fuse 10 in the fuse panel. Fuse 9 receives its power from terminal 15/54 of the ignition switch. I'm thinking both fuse 9 & 10 should have power at their top contacts when the ignition switch is in the "run & Start" positions. If the fuses are good and the contacts clean there should also be power at the bottom of these fuses.

I think the Fan relay is located on the drivers fender well under the hood. The wire colors going to the relay should be: Violet terminal 30, Blue terminal 87, Blue/black terminal 85, white/black terminal 86

I think there is a warning light delay timer mounted close to this relay. It can not be substituted for the relay.

Hope this is some help

Re: Engine fan power. 73 1608.

Posted: Sat Jul 27, 2019 4:26 pm
by Funcar

Thank you for pointing me in the right direction to find the problem.


Here is a picture of the relay. The green wire was burned and easily pulled free. It was actually fried.That was the problem.


Here is a picture of the 5 wires going into the relay. 2 violet. 1 black. 1 light green with a black stripe and obviously the green that burned. When I think about it I had put a connect into the ground which meant the fan always ran. I would think it stands to reason the wire over heated and melt the relay. I hadn't trusted the new thermal switch I had put in!.So that was the problem. ( Amatuer learning from bonehead move.)

I would think my best option is to source a new relay and move on. Do you have any recommendation where I can get one in Ontario Canada?

Substitute auto part?

Thanks again Dave.

Re: Engine fan power. 73 1608.

Posted: Sat Jul 27, 2019 5:16 pm
by spider2081
the relay is a standard automotive "cube" relay. Some people call them Bosch style relays. They are available with 4 or 5 terminals. I think you have a 4 terminal relay but a 5 will work in place of it. Any auto parts store should carry the relay and the socket it plugs into. The socket will not have the correct color wires in it. Bring your relay to the store and they will match it.

Re: Engine fan power. 73 1608.

Posted: Sat Jul 27, 2019 6:05 pm
by Funcar
Thanks again on helping me with my rolling restoration.

Re: Engine fan power. 73 1608.

Posted: Sat Jul 27, 2019 8:01 pm
by spider2081
My pleasure

Re: Engine fan power. 73 1608.

Posted: Mon Jul 29, 2019 11:46 am
by Funcar
I repaired the burned wire with a new connector . I used the old relay as it didn't seem damaged. The plastic holder needs to be replaced. Can someone tell me how to remove it from the fender or how it is connected. I would think I can source from a vendor or some one that sells parts.

I activated the engine fan by connecting the ground wires that attach to the thermal switch. I reconnected them to the thermal switch and went for a drive and brought the temperature gauge to the 200 range or higher but prior to reaching the red zone. I was home in my driveway. I popped the hood and could see the fan was not working. I again connected the 2 ground wires that attach to the thermal switch and the fan ran. The lower rad hose was hot.

Then my car stopped running as the fuel pump stopped working. I left the car sit for about 1/2 hour and the car started right up.

When I get back to the car tomorrow i will trouble shoot why the fan doesn't work in the stock wiring. Check coolant system is properly bled. Check ground wires. Check thermostat ( new). It ihas a new thermal switch. Is there anything else I can do?

Why did my electric fuel pump stop working? Why did it work after my car sat for 1/2 hour.



Re: Engine fan power. 73 1608.

Posted: Mon Jul 29, 2019 12:03 pm
by bartigue
1973 model cars had a mechanical fuel pump. When you ask why your electric fuel pump failed all I can think of is because it's wired into a system that isn't designed for it. Now most electric fuel pump configurations work just fine, but in a car where the electronics have been obviously messed with it represents just one more point of failure.

My reaction to cars with electrical system modifications is to undo the modifications and revert to stock as you move along. Before you "improve" something make sure it works in the first place, then go and add relays or whatever to it.

I never had a problem with mechanical fuel pumps on these cars. If the carb drains back into the tank then its a pressure or fuel problem.

Re: Engine fan power. 73 1608.

Posted: Mon Jul 29, 2019 2:16 pm
by zonker
What temperature fan switch is installed?

Do you have a laser thermometer that you can point to the bottom of the radiator to compare temps when you suspect the fan to engage?

Where is the electric fuel pump getting it's current from? The same 16 amp "A" fuse? Or the pink wire on the fuse box?

I think your '73 should have it's OEM wires like my '71, Fan current flows on it as follows:

Battery positive cable > Starter 13mm nut > Black wire > Fuse "A" > Purple wire > Terminal 30 on relay > Terminal 87 on relay > Lt. Blue wire > Fan positive connection.

Battery ground cable > chassis connection near battery > Chassis ground stud on fenderwell near voltage regulator > black wire > Fan ground connection.

Battery positive cable > Starter 13mm nut > Brown wire > Ignition switch > Pink Wire > fuse box > Blue/black wire > Terminal 85 on relay > Terminal 86 on relay >White/black wire > Coolant thermal switch > White/black wire > Radiator fan ground connector > black wire > Chassis ground stud on fenderwell near voltage regulator > Ground cable connection at battery.

Re: Engine fan power. 73 1608.

Posted: Tue Jul 30, 2019 9:50 am
by Funcar
Thanks for your response Brad.

The wiring in this car is pretty much how I recieved it. To me it looks like there are too many wires and as I know that this car was a combined 73 and 75 or higher car I think it has both wiring harnesses. I could be totally wrong as I don't have any other Spiders to compare it with as this is my first Spider and there are not a lot of other ones in the area. I was a bit surprised when no one said anything about the pictures I posted of the wiring inside the engine bay and under the dash. At any rate this is a winter project and I would like to get some driving fun in during our short Canadian season and have lots of other stuff to do!

Here is the picture of my electric fuel pump. You will note the battery is in the trunk!I replaced the old electric fuel pump as it wasn't working. You can see a red wire ( power) which runs from the number 10 fuse down the inside of the floor carpeting to the fuel pump. It has a 16 amp fuse.

I am interested in your comment about pressure build up as a cause for it to stop working and will start another thread on this as I think it has more to do with gas line plumbing and the ports on the carburetor that are blocked off.

Zonker. I bought the thermal switch from AR and told them what engine size so know they would have sold me the correct one for this car. I don't have a laser thermometer and may pick one up to run this check. I agree the gage may not indicate the actual temperature near the switch and thus it doesn't activate. As mentioned above the fuel pump gets it power from fuse 10 (L) and it has a 16 amp fuse. The engine fan is wired to fuse 1 (A) and it is also a 16 amp. fuse. It passes through a relay attached to the fender and you can see the wiring in my pictures above of the 5 wires going to it. 1 black, 1 green with a black stripe , 2 violet and the green power wire that goes to the motor of the engine fan.

I bled the coolant system again last night and will test again today.