BZT8FS

Thanks yenpit, we've pretty much zeroed in on and mitigated most issues now. The schematic you included is the primary one we've been working with as well as two or three others with more specific detail. I do have the factory service manual specific for the 1973 model year only and it does have some additional wiring detail but is deficient in specifics, particularly with the wiring under the dash that comes in through the firewall so it's been a lot of trial & error. The primary issue was that the turn signal switch was frozen solid, we removed it and in the process of freeing it up heated it quite hot with a heat shrink gun, this inadvertently melted some solder inside the turn signal switch and I never thought to verify electrical connections before reinstalling it. Getting that corrected fixed the major issue, there's still one additional situation that we're hot on the trail of. I appreciate the input! We still have more hills to climb, mostly around the hydraulics once we finalize the electrical stuff.

Corrected an error in labeling the terminal numbers on the back of the switch, had the correct wires in the proper locations. Also discovered that in "Lock" position #4 (LB) wire connects to #2 (BW) wire. I have no idea why at this pointt.

Hi yenpit, Thanks for the reply. The issue isn't with the mechanical portion of the ignition switch. It's the actual removable electrical switch at the back with the 5 pin connections. Mine is flaky in the "On" position. So I ordered an aftermarket one that others had good luck with. It didn't work so I ordered the OEM Factory version 48750-E7705. It operates the same as the aftermarket one. The issue is that in the spring loaded "Start" position, there's no connection to the BY wire going to the starter solenoid. The existing switch does connect BY to WR & the others shown in the schematic in "Start". Neither of the two replacements I have ever connect anything to contact #3, the BY solenoid wire. So something is different in my '73 wire harness than in the earlier cars. I'm not finding what it is and so far have been unable to identify a replacement switch. Thanks, Paul

Thanks banzai510(hainz), I believe that I've verified there are two versions of the ignition switch between the existing one in my car and the BeckArnley replacement I have (visually they look identical , electrically they're not). I've not bee able to determine what the correct p/n for mine is. I'll PM icehouse, thanks for the tip. Good point, I'll have to track down where I connected the fuel pump, mine also has the aircond fuse. I have the pump underneath in the rear just in front of the cross member and the wire disappears inside somewhere. That could be an extra load causing some of this.

Hi datzenmike, Apologies, I wasn't clear. My 510 and all the ones I recall working on (perhaps fuzzy memory) have a connector that can be disconnected, the wires are not soldered on like the one you showed. The switch part itself is held in place with two screws and can be replaced with the main ignition key mechanism in place (see below - I really like the drag & drop now). Beck Arnley claims their replacement switch is compatible, it's not. It does not connect the BY wire to the WR wire in start position like mine does. It's a very well made switch from Taiwan. There are many claiming compatibility on Google & on eBay, but I've not been able to determine the specific part number I need. That's what I was asking. Thank you!

Yes - build date is 12/72. That first digit really looks like an "8" but it's really faint, so good guess on "2"! Interesting that they put a CB there, it's also fused. Any ideas on the ignition switch p/n? Thank you!

It's been awhile. Some progress, we’re making good headway. Looks like I can now drag & drop some files, I hope you can see them. The primary issue was that the turn signal switch had the soft short to ground that we’d been trying to find. I must have caused that when I heated it up to unfreeze it, when we started on this adventure it was frozen solid and would not rotate to either left or right to activate the turn signal. When you all pointed me back to this I found different resistance across the left turn versus the right turn as well as about a ~30 ohm short to ground, i.e. our "soft short"! We never did determine exactly what was causing the issue; we blew the switch out with high pressure (a bunch of gunk flew out) and then sprayed it liberally with contact cleaner multiple times. The resistances are both very nearly equal now to within my ability to measure these small resistances. The flasher flashes properly for both left & right, all bulbs flashing correctly. One of you commented that the entire load goes through these turn signal switch contacts - and indeed it does! I can see why these wear out; LEDs will definitely extend the life of this switch. It's odd that they didn't use a relay, they have relays for virtually everything else. Now I have adequate voltage at the coil during starting to run the engine. However, I've found another possible anomaly (yes, this really is a nit, but annoying): If I operate the starter with a remote switch between the battery positive on the starter solenoid and the solenoid activation tab where the BY wire goes, the voltage drop at the coil is roughly 2 volts, I see 10.4V at the coil with 12.4V at the battery. If I use the ignition switch with the BY wire hooked to the solenoid, I see 9.8v at the coil with a 12.4V at the battery. No other changes. Tracing this through the ignition circuit, we've found that the ignition switch is the culprit for this extra 0.6V drop (I believe it was banzai510(hainz) who predicted that the ignition switch could be an issue. We verified that it's the switch by pulling the connector and connecting the #1 (WR) connection to the #2, #3, & #5 with 12 AWG wire (yeah it sparks when connecting #3, but we only do it briefly, long enough to measure the voltage with the engine turning over). When doing so the voltage at the coil is the same as when using the remote switch, 10.4V so it appears that the ignition switch isn't up to the job any longer. I ordered a replacement (Beck Arnley #201-1174) but it didn't work electrically at all in "start position". Measuring it electrically and looking at the schematics online, I see one difference; on some the #2 contact is connected to the #3 & #5 (as well as #1) in “start” but on others, there's no connection between #2 & #3 in “start” position (that's how the Beck Arnely is constructed). It's not clear how the starter solenoid would activate without a connection from #1 (WR) to #3 (BY) which goes to the solenoid, perhaps earlier cars had different wiring. Is anyone aware of this difference; is there a part number available for the version like mine which does connect #1 to #2, #3, & #5 in "start" position? These switches are not user friendly to take apart and service. I've attempted to load an image with the differences from the schematics here: https://ibb.co/xS1whtx I also attached the image below, hopefully you'll be able to see one or the other.

Wow! Thanks everybody, I really appreciate the support! - banzai510(hainz) - not measuring through the flasher, just the turn signal switch, completely disconnected from everything. - nathan.is.an.idiot12312 - Better searching that I. I wasn't able to find a 510 unit at all. Pricey! I'll look at the others as possibilities Thanks!! - datzenmike, Many thanks! you've been through quite a bit! I must not have mentioned it but when we started on this project, maybe back in August, the frist roadblock was that the turn signal stalk was frozen solid, wouldn't move. We took it off the steering column and had to use quite a bit of heat to get it to the point where is would move enough to flush out that old tan/red grease that had hardened in place and unfreeze it to get it working. Never thought about verifying the electrical connections. Based on what you just described, I'm wondering if we melted some solder. The 30 ohms is just the turn signal switch, completely disconnected from everything. Flasher is not in the circuit. - Stoffregen Motorsports, Thank you. I am now suspecting that we melted some solder inside the switch area when we unfroze it. The wiper arms were also frozen from the hardened grease. I'll bet there's a solder blob like Mike described. I've read horror stories about getting that switch apart between the balls, springs, contacts, and the phenolic card it's all mounted to. It's definitely a candidate for a 3D printed part. The issue that I had was that when the key was in the "on" position, the voltage at the coil had dropped down to like 8V (with a ~13V battery) the starter is directly attached to the battery cable so the engine turned over fine but with the extra draw in the battery there's basically zero spark. While I have tried starting the engine yet, I'm confident that we're past that issue - as long as there are not other electrical issues lurking there.

Alright, delayed update. Had some time last weekend and a few hours this weekend. Zeroing in on the issue. We've verified that the resistance of most of the wires between the fuse box and their destinations under the dash have essentially zero resistance, as you'd expect with copper wires. We've buzzed out most of the wires under the dash now. Remember that we'd identified the green wire from the fuse box coming out of the "Flasher" fuse 2nd one up on the left as having high resistance and 1 amp across it with battery hooked up, noting turned on, and the key out? The green wire goes a couple of places and ends up over at the turn signal switch on the steering column and is the single connection plug next to the 4-pin plug. It goes under the dash and branches to the hazard flasher switch, to the dash instrument panel, & clutch switch. When the hazard switch is in the off position it routes the green wire through the turn signal flasher and then over to the single green wire connection on the steering column turn signal switch. With the battery disconnected and key off, if the hazard switch is pulled on, that branch going to the turn signal flasher and steering column switch is isolated. This branch has high resistance. Disconnecting the single green plug and 4-pin plug to the turn signal switch. Measure resistance between the green wire and the right turn signal wire (#4, Green/Black) with the right turn signal "on" there's nominally zero resistance. Now repeat for the left turn signal - Ah-Ha! This is where the issue is. Measuring between the green wire and the left turn signal wire with the left turn signal "on", resistance is about ~30 Ohms. Tried spraying contact cleaner, it helped a small bit but really didn't change the issue, can't really get the spray inside. Next I need to measure between the green wire and ground - I suspect there's an issue in the switch case. I was running out of time and didn't finish up all of the diagnostics I wanted to but it appears that the "soft short" is in the turn signal switch. I'm pretty sure these are no longer available to purchase so I'd have to take it apart and see if I can repair whatever is the cause. Does anyone have a photo of the turn signal switch taken apart?

Thanks! I appreciate the inputs, when we're in the middle of it we don't think things through real well. The only scenario that makes sense to get the fusible link smoking is if somehow in the "On" position the BL wire from the "Start" position is shorted to ground, that's the only way I can see that happening - raises suspicion that the ignition switch is not well. To your point Datzenmike, there should not be any current flow across the flasher fuse when everything is off. So we started measuring some resistances, with the fusible link disconnected measuring from the BW wire going into the fuse box and to ground at the battery, we get ~10 Ohms (should be zero). Then things get even odder. pulling on the parking lights, resistance drops to ~9 ohms, pulling on the headlights, it drops even further to ~1.2 Ohms. Then in that condition if the right turn signal level is activated the resistance goes up to ~9 Ohms, if the left turn signal is activated it goes to 6.7 Ohms. So something is not right. We haven't been very methodical about this and have spent a lot of time chasing things around, so next time we're going to measure the resistance of each of the wires between the fuse box and the switches (Ignition, Headlight, Turn signals), then we should be able to pinpoint which one has the high resistance and correct it. Do you know if there's a body ground for the wiring harness under the dash somewhere? If so, where is it? Many thanks!

We have SMOKE! Haven't had a lot of time the last two weeks, but secured all wiring that I had apart for diagnosis and thought I'd give it a go to start the engine using my external thumb switch (Snapon) between the solenoid BW wire terminal and battery positive at the solenoid. When we tested this config a couple of weeks ago, the voltage at the coil didn't droop much when running the starter this way. So with key in the "On" position I started to crank and the green fusible link wire by the fuse box started smoking, so I immediately pulled the positive battery cable. Couldn't see exactly where the smoke was coming from but when I measured temperatures in the area with my laser temp meter, the connector on the engine side between the BW wire and fusible link wire was the hottest. This is the connection that I could not get apart, the connection on the fuse box side come apart as expected. I don't want to use pliers to pull it apart until I have a replacement fusible link in hand. This BW wire after the fusible link goes into the the fuse labeled "Flasher & IGN" (2nd one up on the left)- the one with the green wire going through the firewall that we previously identified as the one that appears to have the soft short we've been chasing. I pulled the fuse and put an ammeter in circuit in place of the fuse. With the key out & off just attaching the positive battery terminal I get 1 amp flowing across that fuse station. Nothing is on. I'd expect no current. We tried having the key in "ACC" & "On" and turning on headlights, high & low beam, wipers slow & fast, etc. The highest current we saw was around 2 amps. No idea why the fusible link started smoking. I did find something puzzling that maybe you're run across. I've been using the very nice "DAMB Productions 1997 Rev E." schematic as a reference. I started looking at the "2001 Mitchell Repair Information company" 1973 Datsun 510 schematic because it specifically says "1973". I find one difference between these two schematics in this particular area. It shows the fusible link going to the BW wire but the a little further on it shows "Resistance Wire" with BW on one side and the other side coming out as BL. Anyone run into this before? Any idea what or where "resistance wire" is? Is that an error or something real? Thanks Everyone, more later. For those of you with a three day weekend, enjoy!

When "ON" & 3rd fuse down on the left labeled "Flasher" is pulled and nothing else is on, then same as battery. When fuse is in then no. Regardless of fuse position, if lights, low beam, high beam, or wipers are on, then does not match battery.

The fuse that I remove that makes things better (we're removed each, one at a time to find any improvement) is for the emergency flasher (i.e. hazard lights) and the hazard lights operate correctly. The turn signals do operate correctly when the ignition is "ON" - but to your point, we're not activated them during any of our testing, I'll add that as well.

All coil voltages shown are at the disconnected wires; wire to ballast disconnected and the coil ballast bypass disconnected. I'm at a loss to understand how anything from the flasher circuit would be putting a small voltage on those wires. The flashers operate correctly and there does not appears to be any electrical path to those wires from the flasher circuit on the schematic. Next step I'm going to measure the current flow across the flasher circuit with battery connected and everything off. But that will have to wait until next weekend, we're getting massive wind & rain here today.

Continued troubleshooting. I thought we were on to something here datzenmike, unfortunately doesn't look that way. Nothing points to the ignition switch or the fusible link: Here's what we've diagnosed so far. Battery voltage 12.6V (stays constant except when high beams on, then down slightly 12.56V). 1) Battery connected, nothing on, key out a) White/red wire on ignition switch contact #1; V=12.2 (Using multimeter pin probe into wire right at connector on ignition switch) 2) Battery connected, nothing on, key out, flasher fuse pulled a) White/red wire on ignition switch contact #1; V=12.6, same as at battery 3) Battery connected, key "ON" position, flasher fuse pulled 1) White/red wire on ignition switch contact #1 & BW wire to ballast resistor (wire disconnected from resistor); V=12.6, same as at battery (same on BL disconnected coil wire when in "Start", (solenoid disconnected)). 4) Battery connected, key "ACC" position, flasher fuse in 1) White/red wire on ignition switch contact #1 12.2V; a) pull headlight switch to parking lights (1st position) 11.53V, b) pull headlights on (low beams) 11.23V, c) pull high beams on 8.8V 5) Battery connected, key "ACC" position, flasher fuse in 1) White/red wire on ignition switch contact #1 12.2V; wipers on ranges from 11.23V - 12.00V as wipers cycle. Pull flasher fuse voltage goes up ~0.5V (11.73V-12.2V); pull on high beams w/wipers on, contact #1 ~8.3V 6) In condition 5, headlights on low beam, 0.3V appears on coil wires, when high beams on 0.6V appears on coil wires (goes back to zero when flasher fuse pulled) Disconnect voltage regulator connector, no change to the above. Disconnect WR wire on alternator, no change to the above. With regulator conector and alternator WR wire still disconnected: Jump from battery positive terminal on starter solenoid (accidentally touch other end to ground and weld alligator clip to ground and burn wire off of alligator clip, arrrrgh, get new jumper) to white wire that changes to White/Red to contact #1 on ignition switch, no change to above voltages. Disconnect battery positive terminal cable. Jump from battery positive terminal directly to white wire, bypassing fusible link, no change to above voltages Tried multimeter ground to car body, to engine block, and directly onto the negative battery terminal (and all at the same time), no change (voltage on both coil wires match whatever voltage is on contact #1, when key is "ON" or "Start") The puzzle continues....