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Anti-run valve wiring fix - who posted it?

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Brosky

Brosky

Great Pumpkin
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A while back, during a post about batteries going dead mysteriously, it was determined that there exists a wire that may be grounding out, causing the said valve to stick, thus draining the battery. I think that there may have been a possibility of a defective oil pressure switch as well.

I thought that I bookmarked the fix, but didn't. Anyone remember that and who posted the fix? I think the gentleman is an electrical engineer who designs relays and such for a living and was kind enough to explain the issues in detail understandable to a layman. Sadly, this layman wasn't smart enough to print or bookmark it.

As always, thanks in advance....
 
Paul - on p.107 of Rick Astley's "MGB Electrical Systems" book, he says "without the oil pressure switch, the anti run-on valve would be operating with the ignition off, resulting in a constant current drain which would result in running the battery down."

Here's a link to that Astley quote:

https://books.google.com/books?id=b55_ZAs...buk&output=html

Sorry I couldn't find the post you're looking for, but my old 76 MGB had this problem. The anti run on valve was always in the circuit and draining the battery.

Hope this helps.
Tom
 
Hi Paul,
This post sent me back to my Bentley manual to see which wire you need to examine. You have to check the condition of the white with purple trace wire between the solenoid and the pressure switch. If there is a ground condition in that one your anti-run on solenoid will never turn off and drain your battery.
 
Roman,

It is an intermittent condition, so I suspect a rubbing of a wire in the harness to ground that may or may not occur as it moves away from contact. Thanks for the tip on where to look. As soon as it's warm enough to work on it, I'll peel back the harness and start checking wires.

Does you manual show the specific placement of the three wires on the switch? I suspect these may have been moved during the clutch slave and master replacement.

Thanks again,
 
Anti-run valve?

Sounds like something in a joke played on a newbie mechanic!
 
https://cgi.ebay.com/ebaymotors/TRIUMPH-T...084839020QQrdZ1
antirun.jpg
 
It's a bad Lucas $60 joke if yours fails.

The only problem with disconnecting it is that the oil pressure, brake and ignition light don't work properly with the wires pulled to prevent the battery from going dead. Not a bad trade, since I still have a pressure gauge to watch, but not good for the brakes just in case.

I really don't need it and would appreciate if our resident guru electrical engineer Roman, would figure a way to rewire one of the old style switches into eliminate this switch all together.
 
Paul,
On the spade terminals of the switch there should be some letters stamped into them, P, S and I.
P= Black wire
S= White with Brown trace
I= White with purple trace

Hope this helps you.

BTW I had a similar problem as you but was able to trace it to a faulty pressure switch.

Good luck! /bcforum/images/%%GRAEMLIN_URL%%/hammer.gif
 
<div class="ubbcode-block"><div class="ubbcode-header">Quote:] BTW I had a similar problem as you but was able to trace it to a faulty pressure switch.
[/QUOTE]

That's exactly when the problem seemed to start. After I replaced my leaking switch for a malfunctioning, "but dry" switch.
 
Roman, now that I have the anti-run on disconnected, does it matter which wire goes to which terminal on it? That thing is a real pain to get at, but I'll pull it out if needed.

When it gets warm.....
 
Thank you very much! That advice will save me one sore back from the bending over. I'll get a new switch ordered tomorrow.
 
OK, it was finally warm enough to get this partially checked out tonight.

Ignition key is off.

I installed the striped wires on the switch as instructed.

As soon as I tried to connect the ground, the AR valve started clicking and the connector on the OP switch was sparking (just normal stuff).

I switched the wires around, same issue. The valve would sit there and click. Put the wires back to correct positions and I start the car, the ignition light works, brake light is out, but I never see the yellow oil light on. However, I do have great OP. Shut the car off and the valve is clicking on and off again with the key off (two or three times after shutdown).

I go to the AR valve with test light and ignition turned off. Connect test lead to black and red wire going to valve and it's hot??? The other lead is dead. Why would red/black be hot with the key off? Could this be the problem? I disconnected it, so that the battery wouldn't drain overnight.

Or is the OP switch possibly bad? I discovered one slightly loose terminal on the switch, but jiggling it around doesn't make any difference. That alone will make me get a new one tomorrow.

Any thoughts? I did not have time to trace the white/purple wire out to see if it's grounded. All of my harnesses look free in the holders and show no signs of being smashed or cut in any spots, but that was just a quick eyeball.

Hopefully, tomorrow will be decent and I can get this resolved.

This did correct the brake light being on at all times, which leads to another question. How many wires are supposed to be going to the brake pressure switch on a 74? My connector has to, but one is cut at the very bottom of the connector and I sure as heck didn't do that. The one that is cut looks to be blue or green from the tiny little stub that remains.

Thanks!!
 
It looks like I'm going to have to get deeper into the white purple wire based on guzzul's post below to another thread I had on the replacement switch. I nearly forgot about that advice. But I am going to try a new switch first.

<div class="ubbcode-block"><div class="ubbcode-header">Quote:]When you turn the ignition switch off, power cut from the ignition circuit and from the OP light, but is applied to the anti-run on valve. The valve has a ground available through the OP switch because there is still oil pressure while the engine is turning through its last few cycles. This circuit energizes the anti-run-on valve, which applies a little vacuum to the carb float bowl, enough to stop the engine from drawing fuel.

As the engine comes to a stop, the oil pressure drops below 5-8 psi and the switch flips to open the run-on ground and close the OP light ground. So the run-on valve should now de-energize. Voila.

So if you do have a short to ground in that white-purple wire coming off the anti run-on, when you turn the ignition switch off you have a live circuit, which would keep the valve on (and drain the battery).
[/QUOTE]
 
Hi Paul - you may well have a bad OP switch. When they fail they can give some unpredictable results. But as per your testing, here are some thoughts:

Brosky said:
Ignition key is off. As soon as I tried to connect the ground, the AR valve started clicking and the connector on the OP switch was sparking (just normal stuff).
Click to expand...
This would indicate a 'live' ground - which you should NOT have when the oil pressure is low.
Brosky said:
I switched the wires around, same issue.
Click to expand...
Switching the wires around on the anti-runon valve will produce the same effect. The valve has no polarity, so it doesn't matter which wire is on which terminal of the valve.
Brosky said:
I go to the AR valve with test light and ignition turned off. Connect test lead to black and red wire going to valve and it's hot??? The other lead is dead. Why would red/black be hot with the key off?
Click to expand...
This is correct operation. The red/black (red/brown maybe?) wire is hot when the ignition is switched off. This is not a problem. The problem is with the ground wire. When you say "the other lead is dead" I assume you mean it has no voltage on it, which it should not. But did you check that same lead (usually White/Purple) for continuity to ground? If you have continuity to ground on that wire, plus the red/black wire is 'hot' - then that, in fact, is your problem. You have a live circuit across the valve.
Brosky said:
Put the wires back to correct positions and I start the car, the ignition light works, brake light is out, but I never see the yellow oil light on. However, I do have great OP. Shut the car off and the valve is clicking on and off again with the key off (two or three times after shutdown).
Click to expand...
Again, my apologies about the possible differences between Spits and TRs, but on a Spitfire neither the ignition light nor the brake light should have much effect on this problem (unless there is a short somewhere inside your wiring harness). The only commonality between OP, ignition and brake lights is that they go through the same fuse.
The oil pressure light should come on when there is low pressure and the ignition switch is 'On' (e.g. with the ignition switch On, but the engine not started), and it should turn off after the engine starts and oil pressure builds.
After you shut down, the AR valve should come on ONCE only (i.e. one 'click'), while the oil pressure switch senses that the oil pressure is still temporarily high. When the oil pressure drops it should click 'off' once. If it is clicking on and off multiple time you have an intermittent circuit or you have a bad valve. My guess would be intermittent circuit through the OP switch.

If you want to test the continuity of the OP switch it is very easy to do. Connect an ohmeter between the 'common' terminal and the OP light terminal. With the engine off (no oil pressure) this should show continuity. The common to AR-valve terminal should show NO continuity. With the engine running (oil pressure high), these results should be reversed.

If the terminal(s) on your OP switch wiggle, or if you suspect that the switch is not sensing oil pressure correctly, I would replace the switch. These are inexpensive (see other posts about GM replacements, about $10).

If you wire the switch backwards (reversing the AR terminal and the OP light terminal, but have the 'common' terminal correct) then you can get a condition that results in power on the AR valve and a permanent path to ground with the ignition off. If you wire it as per RomanH's post you should be ok.
 
OK, I think the case may be solved, provided that I don't wake up to a dead battery due to an intermittent issue. (Or a dead short that isn't making contact now)

Luckily, one of the old time parts stores (yes, like hardware stores, they still actually exist, though somewhat rare) found one in their warehouse and had it picked up on the afternoon run (yes, they actually do believe in customer service) and I bought a new one for $9.95. Before I went over to get it, I removed the old one and low and behold, white/brown terminal was moving up and down. I never noticed this before. So I installed the new one and no crazy clicking when I hooked up the A/R valve. I started the car and heard the click when I turned the key on and ran it until it was warm. Shut it down, one click after and all seems well.

Ignition light comes on when I turn the key on and the brake light stays off.

Possible mission accomplished. Thanks to all, especially to Ross and Roman for the walk down electrical lane. Not exactly my favorite avenue of repair, so I appreciate the help.

Tonight, I'll solder in some new ground terminals and a new terminal on the white/brown wire and this one should be behind me.
 
Brosky said:
I started the car and heard the click when I turned the key on and ran it until it was warm. Shut it down, one click after and all seems well.

Ignition light comes on when I turn the key on and the brake light stays off.
Click to expand...

Oops. Sounds like your OP switch was a problem all right, but I'm not sure about what you're experiencing now. Maybe I'm not reading this right.

You should not hear the anti-runon valve click on when you start the car. At that point it should have no power and no ground. Also, when you shut the car off you should hear two clicks. Once when it engages (immediately after you turn the switch to 'Off'), and then a second click maybe 10 seconds or so later when the oil pressure drops and the AR valve loses its ground circuit.

Does the oil pressure light come on properly when you turn the ignition switch on (before you start the engine)?

Double-check the wiring at the OP switch. If necessary, use the ohmeter to make sure which direction the switch it 'grounding' to when the engine is off and when it is running - just to make sure you're plugging the right wires on it.

It sounds like progress, though.....great.
 
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