Main beam fuse issue

sspencer · 05-17-2009, 02:02 AM

Guys,

I have a 72E that will now blow its main fuse if I click it on to main beam.

I never use the main beam, so the annoying thing is its rego is due in a few weeks, and I am going back to the UK in 10 days - so time is an issue.

Has anyone had this issue before, if so what is the shortest path to success (i.e. rego).

I have checked the bulbs and they are 100W, I assume the headlights are H1, so is this too strong a bulb?

ossiblue · 05-17-2009, 08:43 AM

The implication in your first sentence is that this is a new situation. I will assume that it is happening to only one light circuit, correct? The wiring for the 72 is pretty straight forward for the headlights so I would suspect you are shorting to ground on the main beam circuit.

Check all connections at the headlight to be sure they are insulated. Check also at the fuse block. Check the continuity of the wire for the main beam that is blowing a fuse--wiggle the wire with the continuity tester attached to see if you find a break or ground fault. Also, check the dimmer relay for ground faults.

100w bulbs should not blow the fuse, but they are too much for the stock wiring/switch set up. You should put in a headlight relay system and a heavier gauge wire from the relay to the 100w bulbs to prevent destroying your headlight switch and the switch on the stalk (dimmer.)

Let us know what you find. Help is a web-post away.

HarryD · 05-17-2009, 04:04 PM

Assuming you headlamp wiring is stock, you have 4 fuses for your head lights. They should be the same as my '73. In the lower fuse panel you should find:

Fuse 1 is for the left high beam
Fuse 2 is for the right high beam
Fuse 3 is for the left low beam
Fuse 4 is for the right low beam

Now, which fuse is going out?

sspencer · 05-24-2009, 02:29 AM

Hey OssiBlue and Harry,

Thanks for getting back to me. I did some investigation today, and the headlight switch (stalk) smokes for a couple of seconds before the main fuse blows (top one in the top fuse box).

So it looks like the issue could be in the switch?

Harry - my fuse box and Haynes manual doesnt help me with which fuse is which, do you have the list of which fuse is for what for the two boxes?

Cheers - and thanks!

sspencer · 05-24-2009, 02:41 AM

OssieBlue,

I did have an issue with the rhd dipped beam not working. The garage linked the left dipped beam to the right. By taking a new run from the left beam direct to the back of the headlight outside of the std wiring loom.

This worked fine for 6months.

Do you think the two issues (old and new) could be linked?

ossiblue · 05-24-2009, 07:31 AM

sspencer,

Use this link, and click on the electrical diagrams for the 73 911.
http://www.pelicanparts.com/914/914_electrical_diagrams.htm

The smoking switch on the stalk certainly seems to be involved but I'm not enough of an expert on electricals to know if the switch is causing the fuse to blow, or the switch is smoking due to a short that also blows the fuse.

As far as the garage wiring goes, again, just a guess but it sounds like they rewired the left beam because of a problem in the loom--maybe a bad wire. Perhaps the problem you have now is caused by another bad wire in the loom. Just a guess.

Study the diagrams and I think you may be able to narrow down the problem areas. Also, true electrical experts should add to this thread to steer you to an answer. Whatever you do, I'd definitely inspect the stalk switch as you have major overload symptoms in that area.

Keep us up to date, and good luck.