1966 230sl electric fuel pump won't stay on

[ronwall83]

Hello!

I inherited a 1966 230sl from my aunt & uncle. They drove it regularly but it probably sat untouched for over 5 years before they gave it to me...

I'm not a mechanic, so I'll start with that. But I am handy with a wrench and am trying to immerse myself into the workings of this car...

I can get the car running (poorly).  I flushed the tank, updated the fuel lines, just as a starting point.  Here is my issue...when I turn the key to the "on" position, the fuel pump does not start up.  I have to turn & hold the key just passed "on" and before "start" to activate the pump.  However, when I start the car and return the key to "on" the pump quits and car dies.  If I hold the key between "start" and "on" letting the starter disengage, the car will run. But, that obviously isn't a long term solution.

Where do I even begin?  Would seem electrical, maybe at the key switch, but I don't know my way around that type of thing...

[Vander]

You are going to need an electrical test light. Put the key in the on/2nd position. First you will want to check the fuse on the driver's side of the engine compartment. It is fuse #4, make sure you have power going in and out of the fuse. You can also twist it within its metal holder to make sure it has good connectivity.

Then still with the key you, you want to go under driver's rear of the car and make sure you have good power and ground going to the fuel pump. To test for power hook your test light up to a good ground on the car, then if you find out you have a good hot going to the pump hook your test light up to the hot to test the pump ground.

If you don't have a good fuse, hot or ground as mentioned above then which one you don't have is your problem. If all of those test good, then the issue is inside your pump and sending it out for rebuild would make it new and eliminate all future issues.

[Kevkeller]

It sounds like the key ignition switch.  I have taken one apart and cleaned the contacts in it about 20 years ago, so I don’t remember details. It was a 69 280Sl.

I have my steering column out on my ‘70 280SL right now if you need pictures but there are threads on how to take the switch out.

You can also buy a new switch portion I believe.

[ronwall83]

Thank you, Vander.  I'll get to testing.  Would poor fuse contact or poor ground still allow power to the pump @ 3/4 turn?  It won't hurt at all to test everything...but I do get power there by holding the key between run & start.

[ronwall83]

This was my 1st thought, too, since I can get power to the pump...but only if I hold the key between run & start. 

This thing sat in a barn & wasn't touched for 5 or so years.  The interior is moused out...so it wouldn't surprise me a bit if there are chewed on electrical wires, shorts, bad connections, etc. 

My main goal is to get.to the point where I don't have to hold the key just right to run the dang thing.

[BobH]

I think failure of the ignition switch is fairly common after 50odd years service

There's the same symptoms as yours on this post, with a link to some pictures of the open switch, albeit in German

https://www.sl113.org/forums/index.php?topic=33430.msg244134#msg244134

Part of the German attachment translated reads:

Switch is two-part – the plastic part (connections of the cables) and metal part (actual switch) are plugged together and pressed together in 3 places. Plastic part can break or the compression becomes loose - both lead to the current flow being (temporarily) interrupted, especially in the position "2" - ignition ON

[rwmastel]

Ron,

Welcome to the Group!!  If you get acquainted with our Search feature, you'll find lots of information and answers. We've been online 20+ years, so an incredible amount of topics have been discussed and it's a great way to educate yourself.

I'd focus on the switch as well.

If your wiring is all chewed up by mice, a member here makes nice wiring harnesses.

[Cees Klumper]

New switches, that go onto to back of the metal key receptor, are available new for under $100. My car would not start at all until I replaced that switch part. It was easy to install.

[ronwall83]

New switches, that go onto to back of the metal key receptor, are available new for under $100. My car would not start at all until I replaced that switch part. It was easy to install.

Here's hoping! I've read other posts about it being an all day job... Guage clusters to come out, steering column, etc.  Ugh.