750T - Wiring

I bought my 750T six or seven years ago, stripped it down for a rebuild, then left it in boxes whilst I retired, moved and built a house. I’m now back on the case.

Most of the mechanical parts are now refurbished and re-assembled. I have just started on the wiring.

I have managed to obtain an original owner’s manual (actually it’s for a 750 Targa, but I believe that’s what was issued with the 750T) which has a legible wiring diagram.

Unfortunately, some of the bike’s wiring does not correspond with the diagram. For example, the diagram shows two wires connected to the starter solenoid (brown and white/black) - in addition to the main live feed - but there is only one spade connector on the solenoid.

Another puzzle: the diagram shows a white/black wire running from the start/stop control switch to the solenoid. The wire actually runs from the switch to the emergency flasher switch!

Has anyone had similar problems? I’ve frightened my self reading other on-line forums!

May I suggest getting a wiring diagram from Chris950s who is on here. I recently got one and they are fabulous. I have to try and sort out my wiring from some boxes of bits and buggered up harnesses, and I have had some wonderful assistance on here but the diagram is just fantastic and so easy to follow. I am making it all from new. I hope!!!

Highly recommended.

Cheers

Ian

Hello Steve

Attached is a link to Carl Allison’s wiring diagram for the 750 Targa (I have not drawn one for your model yet) http://www.thisoldtractor.com/guzzi007/schematics/1990_750_Targa.gif

There is a single main feed to the starter motor relay (brown wire) from the fuse box. It also feeds the relay coil (two wires in one spade) the black/white wire from the start switch is on the other relay coil terminal when the black/white wire is earthed at the switch the coil is powered up and the main relay contacts close allowing power from the relay to the starter solenoide.

The black/whiote wire is an earth and should not run to the hazard light switch. The hazard switch should have green/black and pink wires that run to the indicators and orange from the flasher unit and black earth wire. If the start switch (black/white) is connected this is wrong and should be altered.

I hope this helps

I would be wary of Carl Allison’s colours, there seem to be a lot of orange wires where these should be red or brown. I will look further when I can…

Thanks all. That gives me something to be going on with.

If anyone wants a copy of the wiring diagram which came with the Targa 750 owner’s manual, let me know. I tried attaching it to this post but the file is too big.

Steve

PS - I agree about Carl Allison’s diagram. Initially, I thought it was a godsend, but on closer inspection it is dodgy. For example, it shows most of the wiring around the ignition units and coils as black, that is completely wrong.

The bike will have a starter relay as well as the solenoid.
The solenoid is activated by a single wire from that relay. The relay will have a power feed (probably jumpered onto 2 connections), a trigger wire going to the solenoid and a switch wire coming from the starter button
I would suggest replacing the power feed wire that goes onto the solenoid with a line direct from the battery (with an inline fuse) Mike will know which terminal number as he is a far more knowledgable whiz with relays and electrickery.

If you’re asking me … :smiley:

Depends which one goes to starter solenoid, if it’s 87, then 30 goes to battery via separate wire and fuse.

I’m guessing there will be two connectors joined by a short loop of wire (?), between 30 and either 85 or 86, pull the one off 30 but leave the other in situ. Not sure of the wire colour for 750T, on mine it was brown I think. Goes to fusebox, fuse #1 ?

relay-terminals.gif

NB: “relay cavities” = relay socket, insertion side, but not applicable here.

Don/Mike

Thank you for your posts.

I can’t see a relay on the wiring diagram. Shall I send you both a copy? If yes, I will need your email addresses as the file is too large to attach to this post (no, I can’t imagine why either!)

Steve

There will definitely be a starter relay on the bike somewhere along with a solenoid that is piggy backed on top of the starter motor.

Don

You are a star and I am blind.

The wiring diagram references a component (No 39) as “starter solenoid”, I think it is actually the relay to which you refer - I still have to check. On closer inspection of the diagram I can see that the solenoid is shown as part of the starter motor (No 40).

Watch this space!

Steve

The starter solenoid is a heavy duty component that sits piggy-back onto of the starter motor (as Don said) it is activated by the starter relay. On your wiring diagram it is all part of the starter motor (component 40) the starter solenoid is drawn at the left hand end of the starter motor graphic, where the red wire comes in from the starter relay (component 39). The starter relay (component 39, but confusingly called the starter solenoid on your wiring diagram) sends a high current to the starter solenoid via the red wire. The starter solenoid then engages and boths sends power to the starter moter making it turn and pushes the starter motor pinion onto the toothed ring around the fly wheel so starting the engine to rotate.

The starter relay (component 39) is there so you don’t have a high current passing through the handlebar start button. The balck/white wire is an earth to the relay and the starter button connects it to the earth on the bike. The brown wire (relay terminal 86) connected to the starter relay is positive and when the starter button is pressed it is earthed by black/white (relay terminal 85) the coil in the relay is energised and becomes an electro magnet, it is this that then closes the switch in the relay letting the high current flow from the fuse box from the brown wire (relay terminal 30) to the starter solenoid red wire (relay terminal 87).

I have numbered the wires as Mike’s diagram above, but note his diagram shows a different type of relay with 5 spade terminals not 4 as the starter relay has.

I hope this helps

Chris

That is so helpful, thank you.

Steve

Well Guys - we have a starter motor! All thanks to you.

Steve

PS - we’ve got a spark too. Time to celebrate.

Result :smiley:

Good news :smiley: