Wiring problems with my 1977 CB750F1

[Stewartgh]

Hi would appreciate anyones help here, I am going mad, I have 2 problems, first is that my tail light does not work, brake light is fine, and tail light works when ignition switch is set to park so I assume buld is OK as park is using the less bright filament as would the tail light, but not in run with 'P' or 'H' position selector switch on, the other problem is the sidelight in the headlamp is not working, same situation, when ignition switch is set to park it works, but not in side light mode!!!
I have found plenty of wiring diagrams but none show the sidelight in the headlamp unit or the separation of the tail and brake light. Any help would be appreciated.
In my headlight I have 1 large buld in the centre, which has 2 filaments, both are working for high and low beam, then there is another small bulb  below the larger one which has 1 wire going to the centre and then a ground, this is what I am refering to as the side light, and this is the one which comes on when the ignition key is in the park position, on the handle bar switch I have 2 positions one is labeled 'P' and the switch lever goes up slightly in this position into an inset part of the groove, and the other position is 'H', which assume to mean 'Headlight'. I took the bike for an MOT recently and the guy at the garage told me that the 'P' switch position should turn on the side lights, (the smaller bulb below the main one in the headlight). this is not working, and in fact to rear light does not come on in that position either, but it is also not working in the main position so that could be a red herring.

[Spitfire]

Had the same problem with my back light, it is a question of following the wires back, no magic bullet, I think in the end I switched the "live" in the headlamp to the old indicator beeper feed. In the end it was a bad connection in the fuse box causing the problem.
The P switch is indeed for the Parking (side) lights.
I'll PM you the wiring diagram from my handbook (1976 CB750F1).

Cheers

Den

[Yoshi823]

Faulty right hand switchgear suspected.

The brown wire that feeds the tail light bulb, the pilot light in the headlamp & the lights in the speedo/tacho are all supplied from the right hand switchgear when the ignition key is in the 'ON' position. The reason that the keyed switch illuminates the tail bulb & the pilot bulb when in 'P' or 'PARK' is because it connects the red to the brown for those circuits, bypassing the right hand switchgear. I would check the brown wire coming out of the switchgear for +12v when selected with the ignition in the 'ON' position. The +12v goes in on the black wire which is the regulated +12v, as against the unregulated +12v which is from the battery via the red wire.

[Stewartgh]

Thanks guys, I am off to take a look now with your comments in mind, and thanks a bunch for the schematic Dan, thats the best one i have seen..... will update later.

[Stewartgh]

OK More descoveries, brown and black in the RH Switch both have 12v all the time, until I switch ingnitiotn to park position at which point the brown loses the 12v, I have dismantled the switch cleaned and reassembled, and when I check the switch operation out with the DVM with no power switched on at ignition all checks out perfectly so I am pretty confidant the switch is good... also I noticed that when the RH Switch is in P position if I turn the indicators on the P lamp in the headlight flashes in time with the indidcators!!!

[Yoshi823]

In which case it sounds like the earth from the plate inside of the switchgear to the handlebars is not too good. Check the continuity from the metal of the switchgear to the -ve side of the battery. I think that the left hand switchgear also earths the metal of the case to earth via the handlebars.

Easy enough to check as long as you have a multimeter or a continuity checker.

[Stewartgh]

OK, Insanity is looming now.....!!! Right I have now disconnected everything in the headlamp, except the brown feed to the 'P'/sidelight and the green ground for the same, still no light when switched to the 'P' position on the RH switchgear, but when I swith the indicators on either side it lights up! Despite the fact that now all the indicators front and rear are completely disconnected. I have dismantled, cleaned and checked out with the meter both handlebar swicthes and the ignition switch, cleaned every connector I can lay my hands on with switch cleaner but still no joy!!! Any further help would be very much appreciated.

[Stewartgh]

WoooHoooo!!!!!!!!!!!!!!!! Yes you guessed it, I fixed it, well it seems I actually caused it in the first place, since I stiped everything down over a year back when I restored it, and surprisingly it passed an MOT then with no mention of the problem,  but for sure it had been there all along, I just hadn't noticed it, till this years MOT...... long story short in the connector box under the stearing head there are a bunch of connections, I had the feed to the RH Switch mixed with the turn signal buzzer, they are both the same colour code (Br/B) but one has a little yellow tag which had slipped up into the loom exit point out of sight!!! So about 15 hours greif as a result of my own cock up..... Thanks for your help Den & Yoshi got me going in the right direction, off to get the MOT finsihed off then I'm on the road.....

[Spitfire]

Great that you got it sorted,that connection box is a pain and the buzzer wire can be confusing.

Cheers

Den

[SteveD CB500K0]

Another satisfied customer   

[theriddler]

Hi, I also almost got caught out with this...! But managed to keep track of little yellow band on wire! I was interested to note that "Spitfire" PMed a copy of the wirirng diag from a 750F1 (i.e. UK/ euro version) owner's manual - any chance that I could get a copy please? Most of the versions I've been found have either been for a euro F2 or an American CB750F...(F1 equiv. but there are some differences...). I've almost got mine on the road - MOT failed on sticking rear brake - will strip caliper & fit seal kit, hopefully that'll sort it! Once going I intend to sort out a few wiring weaknesses...the odd bullet connector or 2 & also maybe a DYNA S ignition...?

[Spitfire]

No worries I'll PM you a copy.

Cheers

Den

[Sprunghub]

& also maybe a DYNA S ignition...?

Not sure how far you intend to go with the Dyna S...but if you have a mind to go for the whole package....& depending on how the Exchange rate sit's at the point when you do it, it may be cheaper to buy from the States....or if you are the cheeky sort, use that to get a discount on a set-up from the Uk.
There is a chap who sells via Ebay (US Ebay) who even inc' of p & p may be cheaper than the Uk supplier if you are buying the coils & plugs set too.

[SteveD CB500K0]

For Dyna S from the 'States, go to www.sohc4.net and ask Jeff.Saunders (that's his user name). He runs www.z1enterprizes.com and has had the best deals for ages.

And he's an SOHC4-lover (disregard the name of his business for a minute - that's historical!)

[theriddler]

Thanks heaps for the wiring diag! I was beginning to think there wasn't one specifically for the F1! also the info on the Dyna S is really good - I'm looking forward to give it a go! Is it possible just to change the ignition - do you have to change coils & plugs?