Fan/horn nonsense

[FordPrefect]

Alrighty, my 77 (appears to have 76 wiring) overheated the other day, so I've been poking around.

Problem: fan never appears to turn on
1. fan works when connected directly to battery
2. relay clicks when i short the thermo switch terminals
3. I get 12 volts at the fan connector with key on and thermo switch shorted
4. that 12 volts appears to not reach the fan when I plug in the connector
5. I've cleaned the connector, wires look ok.
6. Fuse (A, possibly I, depending on year) seem ok, I gave them a wiggle
7. I've actually pulled the wires out of the plastic connector, plugged the spade connectors directly together, and don't get the 12 volts. I only get it when the fan is unplugged from this connector
8. shorting the relay terminals seems to not make a difference.


Another thing I've noticed: horn no longer works.

1. no power at horn terminal

I need to find the horn relay, and check my fuses again, any suggestions, tips, etc?

[So Cal Mark]

sounds like a voltage drop due to a poor connection

[Squidders]

Check the fuse carefully again. I had a similar issue and on close inspection the fuse had a minor crack and would only make contact intermittently. Better still just swap it out.

[RRoller123]

1, 3 and 4, taken in combination, imply that the connector at the fan is bad. Could be either side.

1. fan works when connected directly to battery
3. I get 12 volts at the fan connector with key on and thermo switch shorted
4. that 12 volts appears to not reach the fan when I plug in the connector

[aj81spider]

That's an interesting problem. The horn and the fan share a common fuse, and the horn not working would indicate that you have a fuse problem. I would definitely take Squidder's advice and change the fuse. However having 12 volts at the fan is a counter-indicator to that, so it's possible you have two problems, or that Mark is correct and you have a voltage drop problem. Check to see if you have 12 volts at the horn relay, and if you do check to see if the voltage drops when you press the horn button or turn on the fan.

When you apply 12 volts to the fan and it works are you applying 12 volts to one side and ground to the other? The thermal switch actually grounds one side of the fan motor (go to www.artigue.com and download the 77 wiring diagram if you haven't already), so having 12 volts at the fan is normal and won't make it work. To check Pete's theory plug the fan connector in and unplug the thermal switch and apply ground to the wire there. If the fan doesn't turn on then you don't have a robust 12 volts at the fan (i.e. either the fuse is bad or Mark's theory about voltage drop is correct). If the fan does turn on then you have a bad thermal switch that is not grounding the fan (and you have a separate problem with your horn).

[RRoller123]

If #1 didn't use the ground pod (G1) ground for the fan, but directly grounded back to the battery, or another ground, then 1, 3 and 4 taken in combination, more directly imply a bad ground at the pod, or a break along the wire going from the fan to the ground pod. Check for ground continuity along this run. Here is the schematic:

[spider2081]

Some year Spiders did have a relay between the fan motor and the radiator temp switch. This is more than likely the relay you hear clicking. I don't know where the relay is located. I would suspect if it were in the engine compartment you could have found it from the sound. So I think it might be mounted under the glove box.

I would suggest you get a trouble light and a voltmeter and make some tests. Learning to use these 2 tools will remove much of the anxiety of electrical problems with your car. Your symptoms could be as simple as a bad relay. It does sound like a poor connection somewhere in the circuit. Finding the relay and testing from that point is a good direction to pursue.
Let us know how you are doing

[FordPrefect]

If #1 didn't use the ground pod (G1) ground for the fan, but directly grounded back to the battery, or another ground, then 1, 3 and 4 taken in combination, more directly imply a bad ground at the pod, or a break along the wire going from the fan to the ground pod. Check for ground continuity along this run. Here is the schematic:

Hey, now that's a great schematic!

[RRoller123]

It is from an available online set I bought 5 years ago for a few bucks, bound. Only applies to 1980 and maybe a couple of years afterwards, but they are generally all pretty close. Get one specifically for your year! Get the shop manuals too, they are very helpful.

But ALSO, Brad Artigue has kindly donated color coded schematics on his web site that you can download for free.

Pete

[FordPrefect]

Alrighty, had power at the fuse, figured the voltage was ok at the relay, but maybe not enough current? traced the power wire up to another connector just before the firewall and cleaned the terminals. Boom, we have fan and horn again!

As a side note, I don't the the horn has its own relay in my car.