I've heard about this problem before. You've been driving on a warm day and, at some inconvenient stop, the starter won't engage. Dead. Nothing. Nada. Battery is fine but no action from the solenoid. Bump start works and you get back to your home just fine. Next day the car starts as if nothing was wrong. People with more knowledge than I, and they are legion, tell me that this is a common problem with the teener. Thanks for that but I would like to know what the root cause problem is. My car has been run on hotter days for longer periods and this is the first time I've experienced this failure. Is it a wiring problem, a weak fuse, a tired old original part or what? Inquiring minds want to know. Thanks.

(74 2L)

There maybe more than one cause, my experience was caused by an ignition switch that was on it's last leg.

I had that problem, put new starter, no help. Then I was looking at relays on relay board, and one of them was cracked. So l just replaced all of them, since they did look like originals. I haven't had a problem, and thats been 3 yrs now.

If it happens again, lightly tap the starter solenoid with the handle of a screw driver. I've seen that work more than once. Do not replace the starter until you have checked all the easy things first. Relays, switches, wiring etc.

My experience has been that as the cars ages, there is just too much resistance in the stock system when the car gets hot. If you can rule out the other simple things as suggested and can engage the starter when hot by bridging across the solenoid then you need a hot start relay. Original Customs has a pre made one that is really nice. Or you can build your own.

I found this during one of my searches.

Click to view attachment

Nice diagram!

The current has to travel all the way up, through the ig switch, back to the back, through the relay board, and then to the starter. That hot start circuit is a great change that takes the current from the battery directly to the starter with only the relay in the between. Less draw through the key, less current needed to trigger the relay.

Here's one thats all put together , nice clean kit , good price , Bill D.

http://www.thesamba.com/vw/classifieds/detail.php?id=1119538

I had that problem. I decided to take apart the solenoid and clean the out the dust and wipe off the contacts. It took some de-soldering and re-soldering but it solved my hot start issue.

I have similar, but not exactly the same..... This is not really in a HOT situation, but I have noticed it since the very first day I tried to start the car.

I turn the key and sometimes I get nothing... I think I have not turned it far enough and put alittle more turn on it and nothing.

Turn the key off, then FULL to the right and she fires right up. Has never left me stranded.

I was thinking about replacing (what I'll call) the ignition switch. It is the white piece in the steering column that mates with the bottom of the key and the wires connect to the bottom of it. Without the key switch in the car it just takes a screw driver to turn it and start the car.

So which is it for me? Ignition or Hot start relay? Hell for $25 I should do the hot start thingy.

Clark

Could be both.
I still have trouble with the electrical switch portion, which I replaced. There is a tang in the mechanical portion that engages the electrical portion of the ignition switch. Over time it gets twisted backward and wont turn the switch far enough. If I wiggle it, sometimes it will work. If it doesn't I use the push button I have installed. That always works. Even when hot.

I replaced my ignition switch and the problem went away for 3 months! ha... the hot start relay is a good way to go, or go thru your electrical circuit and make sure everything is good!

Adding a 'slave' relay is a good method to save your ignition switch contacts from arching and extend it's life. . It does not fix a defective solenoid with a Hot Start problem. . . It does however give you a better {shorter} path for the yellow lead that operates the solenoid. . This would be effective if the yellow lead, which comes from the ignition switch, has a low voltage /amperage resistance problem.

Electrically, Heat is a resistance multiplier to current flow, and when the solenoid and the battery cables get really hot, there is a higher current resistance and less current can get thru to operate the starter.

Yep, the solenoid can easily be taken apart, It has large contacts inside which are most likely heavily pitted [another resistance location]. . these can be sanded or filed to extend their life. . I've successfully remade the copper contact parts when they were beyond a simple filing. . . The other common big resistance issues for hot start problems are in the battery cable itself, it's connections on both ends, and the Ground Strap at the transmission. Often, corrosion from the battery terminal travels down the battery cable and are present inside the cables insulation cover. .

All the small resistances add up, sometimes individually they aren't much, but in a complete circuit, they are accumulatively over the threshold for the starter to operate when hot

Go with simple first, check the connections and cables before you pull the starter and solenoid. The following is a general sequence to locate the problem source, but multiple issues may mask the real problem. . .
If the solenoid does not click [try to operate] when you turn the key, look for an issue in the large yellow lead, it's connection or the ignition switch. .

If the solenoid clicks but the starter does not turn, investigate the main battery path. . remove the yellow lead, and jump the main battery terminal at the starter to the terminal where the yellow lead was. . You have now bypassed the ignition switch and the starter should turn. .

If it does operate, a slave relay may be your solution. . . If the starter does not operate, look into the solenoid contacts and cable connections. . . . .
You can still have resistance problems within the solenoid. . you didn't fix the issue, you overcame the lower operation limit of the solenoid. . Hope this make sense. .

Typically if your ignition switch is OK.

Its dirty grounds or a dying starter.

the tranny strap design with its open webbing eventually looses its ability to transfer electrical current efficiently.

Get a new tranny ground strap and clean the body and tranny where it attaches.

Get a new ground cable for the battery and clean where it connects.

The car is 40 years old, some starters are 40 years old
Some battery cables are 40 years old.
Most tranny straps are 40 years old.

Ford had an issue, probably still does where whatever they used for cables, or whatever was going on (seen some threads on this, but forget) the battery cables would rot from the inside out...in several years, not even a decade.

The greenies you would find when you open up the cables was the issue...just made it harder to move electricity through the cables.

A relay will mask an issue and allow you to ignore it.
Might not fix the issue at the end of the day.

Thank you one and all for the advice. Good stuff in there and I hope that it helps more than just me.

Ford solenoid fix for 25+ years, never once replaced a switch or cut a single (factory) wire, unless of course someone else already hacked into it.

And that $25 ghia horn relay isn't worth a piece of warm dog shit....IMHO
I have a brand new one sitting in my wire scrap bin, replaced it last year with a real solenoid.

Jack

Personnelly I went this route , I mounted it under the dash & the button only works when the key is ON, the added bennefit is if & when I do stall the car ,I just push the button , I dont have to turn the key back & turn it forward again , Bill D.

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My 1971 914 was not starting in the heat in 1972. Age may be part of it but it is not a new problem.

A follow-up to close the topic. I had the car serviced in June. Yes, I had it done by a shop. At my age it is getting difficult to do the necessary contortions and I never was much of a mechanic. The start problem had mysteriously gone away. Intermittent problems are the worst kind and when this one occurred again in July it was back to the shop. It turned out to be a simple fix; the solenoid was bad. So I am back on the road again. My thanks to all of you who offered various diagnoses.