Author Topic: CB750K8 Electric Issues (Read 979 times)

TravistyOJ · « **on:** September 13, 2021, 10:48:01 PM »

Just got a 1978 CB750K back up and running, and so far it’s been doing well, except for one random intermittent issue. This has happened a handful of times, sometimes during warm up and sometimes while riding, it will completely die. No power, no lights, nada. Almost as if main fuse blew. I will turn the key off, and it turns right back on and runs fine. Battery is an AGM motobatt, and I replaced points with a Dyna S. It doesn’t run rough or bog before this happen, just dies, as if I hit the engine kill switch, but like I said no power to anything at all. Any ideas? Voltages are good, battery is fully charged, fuses are good.

bryanj · « **Reply #1 on:** September 14, 2021, 12:36:40 AM »

Either the ignition switch is dying or the fuse/fuse holder is cruddy and maybe unsoldering the fuse, put a new fuse in but clean an tighten the clips it fits in

robvangulik · « **Reply #2 on:** September 14, 2021, 02:08:23 AM »

And don't forget to check the wires at the back of the fuse holder too!

newday777 · « **Reply #3 on:** September 14, 2021, 04:21:35 AM »

When it happens wiggle the key. The ignition switch is a common problem on the 77 and up style that Honda went to from dirt and water intrusions along with people putting a few keys on the key ring bouncing around(1 key only and no heavy fobs!)is the death of ignition switches.

newday777 · « **Reply #4 on:** September 14, 2021, 04:24:22 AM »

And welcome aboard TravistyOJ. Introduce yourself and your bike(pictures!)in the new members section.

goodtryer · « **Reply #5 on:** September 14, 2021, 04:56:50 AM »

Howdy!

Had the same the happen to me on my 78 750K. Turned out to be a loose connection in the ignition switch:

http://forums.sohc4.net/index.php/topic,61168.msg2155413.html#msg2155413

Your issue could be elsewhere. At the time I fixed this, I also went through all the wiring harness connections and cleaned them up. Took a couple of hours but I've been pleased with the results.

Mr. Mike · « **Reply #6 on:** September 14, 2021, 08:19:31 AM »

Yep, me too. Turn the bars left and sometimes I’d loose everything. Jiggle the harness plug at the back of the ignition switch…ahhh loose lights. New aftermarket ignition switch took care of it.
But I did do like others suggested by polishing a bit the fuse holders and new fuses.

newday777 · « **Reply #7 on:** September 14, 2021, 04:23:25 PM »

And be sure to post back with a reply here when you find the culprit.

TravistyOJ · « **Reply #8 on:** September 14, 2021, 07:26:17 PM »

Thanks for the great responses! As for the fuse holders, I had thought that might be the culprit, as one fuse melted, so I replaced it with one of the modern blade holders, but issue persisted. Luckily today it happened again, and I tried just wiggling the key, and sure enough it clicked back on. So I think it’s definitely the ignition switch. I know I can replace it with an aftermarket, but then my seat won’t have a matching key (I know I’m being picky). Anyone have luck with taking the ignition switch out and cleaning it with some deoxy? Or should I just get over it and replace it?

TravistyOJ · « **Reply #9 on:** September 14, 2021, 07:42:22 PM »

Quote from: newday777 on September 14, 2021, 04:24:22 AM

And welcome aboard TravistyOJ. Introduce yourself and your bike(pictures!)in the new members section.

You bet! I posted in there, thanks for the welcome

Kevnz · « **Reply #10 on:** September 14, 2021, 07:58:37 PM »

Quote from: TravistyOJ on September 14, 2021, 07:26:17 PM

Thanks for the great responses! As for the fuse holders, I had thought that might be the culprit, as one fuse melted, so I replaced it with one of the modern blade holders, but issue persisted. Luckily today it happened again, and I tried just wiggling the key, and sure enough it clicked back on. So I think it’s definitely the ignition switch. I know I can replace it with an aftermarket, but then my seat won’t have a matching key (I know I’m being picky). Anyone have luck with taking the ignition switch out and cleaning it with some deoxy? Or should I just get over it and replace it?

Nothing to lose by trying.

newday777 · « **Reply #11 on:** September 15, 2021, 02:58:56 AM »

Quote from: TravistyOJ on September 14, 2021, 07:26:17 PM

Thanks for the great responses! As for the fuse holders, I had thought that might be the culprit, as one fuse melted, so I replaced it with one of the modern blade holders, but issue persisted. Luckily today it happened again, and I tried just wiggling the key, and sure enough it clicked back on. So I think it’s definitely the ignition switch. I know I can replace it with an aftermarket, but then my seat won’t have a matching key (I know I’m being picky). Anyone have luck with taking the ignition switch out and cleaning it with some deoxy? Or should I just get over it and replace it?

goodtryer posted a link above of his repairing the loose connection in the switch.
http://forums.sohc4.net/index.php/topic,61168.msg2155413.html#msg2155413

Unfortunately the 78K switch set is discontinued from Honda.
You can search for a NOS switch set that might turn up in a sale sometime...... The part number is 35010-393-772.
The switch itself fits about 20 models from 75-78.

Hey! Look what Emgo has available! A repair kit that replaces the electric base for your switch so you retain your keys. You remove the switch from the top tree and pop out the base and pop in the new base. For $8...
https://vi.raptor.ebaydesc.com/ws/eBayISAPI.dll?ViewItemDescV4&item=363476530435&category=177960&pm=1&ds=0&t=1631699670165&cspheader=1

newday777 · « **Reply #12 on:** September 15, 2021, 03:01:17 AM »

Free shipping.....
https://www.ebay.com/p/171198409

goodtryer · « **Reply #13 on:** September 15, 2021, 04:57:26 AM »

Quote

Hey! Look what Emgo has available! A repair kit that replaces the electric base for your switch so you retain your keys. You remove the switch from the top tree and pop out the base and pop in the new base. For $8...
https://vi.raptor.ebaydesc.com/ws/eBayISAPI.dll?ViewItemDescV4&item=363476530435&category=177960&pm=1&ds=0&t=1631699670165&cspheader=1

What a great find! Saving that for future use.

bryanj · « **Reply #14 on:** September 15, 2021, 05:03:01 AM »

Carefull with the repair kit as there are 2 different bases, you need the same number of spade connectors orit wont work.
Also tape the base on securely as the locating tabs are not as good.
Honda used to sell the base seperate as well but i think its only shown on a different model parts list, sorry cant remember which.

goodtryer · « **Reply #15 on:** September 15, 2021, 05:09:27 AM »

Quote from: bryanj on September 15, 2021, 05:03:01 AM

Carefull with the repair kit as there are 2 different bases, you need the same number of spade connectors orit wont work.
Also tape the base on securely as the locating tabs are not as good.
Honda used to sell the base seperate as well but i think its only shown on a different model parts list, sorry cant remember which.

Excellent advice. Thanks.

Bodi · « **Reply #16 on:** September 15, 2021, 12:30:34 PM »

Historically the Emgo switches have had a lower current capability than OEM and they can burn out fairly quickly, adding a simple automotive relay to handle the black wire current is a typical addition when going to their repro switches. I haven't seen the "back only" kit and it may be better than what they put on their complete ignition switches.

TravistyOJ · « **Reply #17 on:** September 15, 2021, 03:56:59 PM »

So upon further inspection, I quickly found the real issue. Looked at the plug connected to the bottom of the ignition switch and on the harness end was the dreaded signature of someone who didn’t know what they were doing, a big gob of black electric tape! Unrolled it and sure enough someone had wedged in a quick-disconnect instead of the proper female spade terminal. Ordered the right one from vintage connections and going to get this thing repaired right

newday777 · « **Reply #18 on:** September 15, 2021, 04:49:32 PM »

Amazing what you can find after someone has been in before you.

News:

Author Topic: CB750K8 Electric Issues (Read 979 times)