idiots guide to electrics

robbajob · 08-19-2004, 03:33 AM

The electrics seem to have gone a bit haywire on my 68 911. First my headlights stopped working, then started again, then stopped again. I think I've isolated this to a loose connection under the dash. Now my horns stopped working and when I switch my mainbeams on one headlight gets dimmer, the other gets brighter, and the blue light on the dash doesn't come on???

I checked my Haynes manual for the horn but the only advice I could find was to check the fuse. When I checked the fuse panel diagram to see which one's for the horn there isn't one there. Can anyone help me?

IROC · IROC's Garage

The only thing I know about electronics is that they are filled with magic smoke. Once the smoke comes out, they don't work anymore. :>)

I don't have any specific advice beyond making sure everything is grounded well. Alot times if more than one freaky thing is happening, it turns out to be a bad ground...

Mike

djmcmath · 08-19-2004, 05:47 AM

I'll concur with that one. Gremlins like this aren't usually magic smoke; more likely bad ground. Hunt around for electrical connections that look ... shady. You know, corroded, worn heavily, loose, etc. Take them apart and clean both sides with steel wool before reassembly. Some people are also fond of using a silicon-based electrical spray, or dielectric grease. Good luck.

Dan

Early_S_Man · 08-19-2004, 07:55 AM

robb,

You can download a colored wiring diagram [in PDF file format, requires Adobe Reader] at Sherwood Lee's Rennlist site, either L57 or L59 will work for your car:

http://members.rennlist.org/911pcars/WiringDiag.htm

Fuse #4 seems to be common for both the horn and headlamp relays, so I would check the fuse, fuseblock, and wires for loose or corroded connection at the screw terminals ...

It wouldn't hurt to check the relay sockets for corrosion, and the relay pins, too! The relay pins can be cleaned with a pencil eraser -- careful, as they are silver-plated! The pins can also be spread a bit with a sharp, thin knife blade ... to improve contact with the socket terminals.

POKDUB · POKDUB's Garage

Suggest you start off with a good circuit diagram.
Here is one for a 911E 1969.

The color dig helps with cable identification and for quickly checking the routing. Print it off in A3 for more detail.

I had a problem recently with my headlights and isolated it down to an broken internal (in the fuse panel, unseen) 12V tie between fuses 1&2 I think. Used a cable jumper to fix, ensure large enough for current carried.

robbajob · 08-23-2004, 01:23 AM

Thanks for all the advice.

Looks like it might be more tricky than replacing a few fuses. Went for a long trip home this weekend (115miles, well it's quite far in England). Stopped off about a mile from home at the supermarket and when I came back out the car wouldn't start. I could hear the fuel pump but nothing else, the engine wouldn't even turn over. Confused, as ever, I had to call out a bloke to look at it. To cut a long story short he wired my battery up to his and it started first time. His diagnosis was a faulty earth somewhere in the engine. Looks like I might have to take it to a shop to get the gremlins, and probably my savings, wiped out once and for all.

LakeCleElum · 08-23-2004, 06:10 AM

I had problems like this once in my '73.5.....I started tracing wires back from the fuse block. Between there and where the wires go in the firewall, I found 5 or 6 bare/burned wires. The fuses hadn't protected them as some of the accessories are fused between the switch and the item. Anyhow, I spliced in new wires and was up and running....Give it a look...

Grady Clay · 08-23-2004, 06:33 AM

The fuse block on ’68 (and ’66-’67) are notorious for failed connections on the back side. I would recommend removing the fuse block and inspecting & repairing the backside connections. Keep the wires in order. If you can find a new fuse block, buy it. Save the old one.

Best,
Grady

robbajob · 08-23-2004, 06:37 AM

Thanks. I'll give it a look.

pwd72s · 08-23-2004, 08:25 AM

One little book that has helped me tremendously is published by Sears.."how to use multitestors"...they have an automotive testing chapter that covers the basics. Warren or Grady would consider it a primary school text, but it helped this electrical bonehead. Oh, I just noticed you're in London. Is Sears over there? If not, PM me with a snail mail address, I'll buy & ship a copy over to you. Cost to me is around $10...hardly worth going to get money changed, so in exchange you could send me something from Brit-land?

Early_S_Man · 05:01 PM

robb,

It may not be that difficult job to get things straightened out ... fixing up 38-year old German electrics isn't nearly as bad as dealing with Lucas electrics, if you get my drift!

Grady's suggestion about the old fuse block is a good one!

My suggestion is to follow-up by removing and cleaning the starter solenoid wiring and transaxle-to-body ground strap.

robbajob · 08-24-2004, 03:08 AM

Thanks. I'll call around and try to find a new fuse block. I had another look through my Haynes manual last night. Not very much use when it comes to electrics. Is there a better book out there that deals with that kind of thing?

Randy Webb · 08-24-2004, 11:14 AM

book: scope out the auto section for a general book at your public library - prob. a section on things. Bosch has various guides also. kida depends on where you want to start.

fuse block: it might be worthwhile to move to a block that takes the new modern tab type fuses - could be more work tho.

Early_S_Man · 08-24-2004, 05:11 PM

Here is a great reference book, with lots of electrical theory and practical information, too ... such as DIN standard terminal numbers, and sample schematics in the 'Current Flow' style:

The Bosch Automotive Handbook
BK-107984B $27.50

robbajob · 08-25-2004, 08:06 AM

OK, before I head off into the world of fuses, relays, ground straps, etc, could someone just give me a beginners guide to safety (if you've read this far and think the safest thing for me to do is take it to a mechanic feel free to say). I've had a look back through the forum and the idea of my fuel tank exploding in my face as a spark arcs from one of the battery terminals to the zipper on my jeans, has left me a little on edge.

Randy Webb · 08-25-2004, 08:22 AM

If the arc is big and strong enough you won't even care about the subsequent explosion -- in fact, you might welcome it.

See my comment above re your local library.