Saturday morning electrical questions

[GB SISSON]

I'm not too smart about electrical matters, so here goes. I bought an interesting electronic tach for my diesel conversion. It has a transducer that attaches to an injector line for it's signal. (Tiny Tach) The instructions suggest it should be wired to the radio circuit, or any circuit that isn't activated while starting, because of surges. Do we have such a circuit on our old fords? (47 truck)... Or how can I create one? Next I have a pair of 12v wiper motors from speedway that look to be a good fit under dash to replace the vacuum wipers. Diesels don't create a vacuum. They have a built in switch, which cannot be reached under the dash. I intend to leave them switched on and switch the wire to them. They also want a 2amp fuse. I assume I'll switch the hot wire, not the ground, but which side of the fuse? Does it matter? And would I jump wire the two wiper motors together? I'll check back later this afternoon as my 92 f350 is up on a friend's lift so we can swap out the grenaded rear axle\. Thanks in advance.

[flatford8]

I’d wire the wiper motor with the switch between the fuse and the motor. Wiring them together would depend on whether or not the wipers “self park”. The tach could be powered through a switch so you know there would be no draw at start up..... Mark

[GB SISSON]

Thank you Mark! Well both solutions seem right on and since nobody chimed in to contradict you, I'll get on these projects right away. I don't see why I'm always having drivetrain problems with my 92. but we got the junkyard sterling 10 1/4 rear in it today . It lives a pretty easy life most of the time at least....

[tomcarman]

Originally Posted by GB SISSON

Thank you Mark! Well both solutions seem right on and since nobody chimed in to contradict you, I'll get on these projects right away. I don't see why I'm always having drivetrain problems with my 92. but we got the junkyard sterling 10 1/4 rear in it today . It lives a pretty easy life most of the time at least....

Loaded up and headed to the scrap yard? If it were me I'd me inclined to hang onto that "junk". Just sayin'.

[40 Deluxe]

Originally Posted by GB SISSON

I'm not too smart about electrical matters, so here goes. I bought an interesting electronic tach for my diesel conversion. It has a transducer that attaches to an injector line for it's signal. (Tiny Tach) The instructions suggest it should be wired to the radio circuit, or any circuit that isn't activated while starting, because of surges. Do we have such a circuit on our old fords? (47 truck)... Or how can I create one? Next I have a pair of 12v wiper motors from speedway that look to be a good fit under dash to replace the vacuum wipers. Diesels don't create a vacuum. They have a built in switch, which cannot be reached under the dash. I intend to leave them switched on and switch the wire to them. They also want a 2amp fuse. I assume I'll switch the hot wire, not the ground, but which side of the fuse? Does it matter? And would I jump wire the two wiper motors together? I'll check back later this afternoon as my 92 f350 is up on a friend's lift so we can swap out the grenaded rear axle\. Thanks in advance.

On the tach question, use a 5 pin Bosch style relay. These relays use 2 of the pins to energize the relay. Splice one into the 'start' circuit, and the other to ground. Next, of the remaining 3 pins, 2 will form a complete circuit when the relay is 'off' (de-energized). run your tach to these two terminals. Leave the 5th pin empty. This way, the tach will operate as normal until you hit the starter switch. Then, the relay energizes and cuts power to the tach and sends it to the 5th pin which goes nowhere. When you release the starter switch power goes back to the tach. So it's all done automatically. No worries about forgetting to turn the tach off!
Wiring diagrams are easily available. I don't know how to post one but I'll go look up the number for each pin of the relay and get back.

[40 Deluxe]

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Originally Posted by 40 Deluxe

On the tach question, use a 5 pin Bosch style relay. These relays use 2 of the pins to energize the relay. Splice one into the 'start' circuit, and the other to ground. Next, of the remaining 3 pins, 2 will form a complete circuit when the relay is 'off' (de-energized). run your tach to these to terminals. Leave the 5th pin empty. This way, the tach will operate as normal until you hit the starter switch. Then, the relay energizes and cuts power to the tach and sends it to the 5th pin which goes nowhere. When you release the starter switch power goes back to the tach. So it's all done automatically. No worries about forgetting to turn the tach off!
Wiring diagrams are easily available. I don't know how to post one but I'll go look up the number for each pin of the relay and get back.

OK, this went quicker than I thought. Each terminal of the relay has a number by it. #85 goes to a ground. #86 connects to the 'start' terminal of the ignition switch. The wire from the tach sensor connects to #30 and the wire from the tach itself connects to #87A. #87 is left empty.
Note that presently your tach wire is one piece going from the tach sensor to tach. You simply cut this wire and connect one end to #30 and the other end to #87A.
If you do a search for "5 pin relay wiring diagram" you'll find lots of them, some helpful, some not!

[GB SISSON]

Originally Posted by 40 Deluxe

OK, this went quicker than I thought. Each terminal of the relay has a number by it. #85 goes to a ground. #86 connects to the 'start' terminal of the ignition switch. The wire from the tach sensor connects to #30 and the wire from the tach itself connects to #87A. #87 is left empty.
Note that presently your tach wire is one piece going from the tach sensor to tach. You simply cut this wire and connect one end to #30 and the other end to #87A.
If you do a search for "5 pin relay wiring diagram" you'll find lots of them, some helpful, some not!

Ok thanks. I was a bit worried about remembering to turn it on and off. Last night in the middle of the night I thought about the unused ACC terminal on my napa starter switch. When I get out to the shop I was going to test that circuit and see if it went off during cranking. Will my local maybe have the 5 pin relay? Edit: Remembered I had some relays from amazon in a box in the shop. I used some on my headlights. Just checked, they have 5 wires. Should work? Tried to copy/paste a link but don't see it.

[40 Deluxe]

If your relays have the Bosch numbering system stamped by each terminal, they should work. The ACC terminal may work, too.

[GB SISSON]

Originally Posted by 40 Deluxe

If your relays have the Bosch numbering system stamped by each terminal, they should work. The ACC terminal may work, too.

Yes, they are bosch clones with all the same numbers. They are pre-wired with pig tails running off a snap together plug which has a blue, double lipped silicone rubber seal at the connection. They came in a pack of 5 for 26 bucks, free shipping. How do they do that? I guess I should try the acc terminal first though.

[GB SISSON]

The ACC terminal was off while cranking and on when engine running, so I went the easy way with less connections. Tach is pretty neat item and works well. I started on the wipers, but didn't get done today. Thanks all.

[flatford8]

I like that relay method.....a lot better than my “backyard” switch idea.....if you come up with that eBay link to the 5-pack of those relays, I’d like to get some....thanks.....Mark

[JSeery]

One thing to keep in mind if you are using relays on a 6v positive ground system is that some of them contain a diode so you need to keep the polarity correct. I did this diagram up for a fuel pump, but it applies to about anything.

[40 Deluxe]

Originally Posted by JSeery

One think to keep in mind if you are using relays on a 6v positive ground system is that some of them contain a diode so you need to keep the polarity correct. I did this diagram up for a fuel pump, but it applies to about anything.

Excellent info! Thanks for sharing

[GB SISSON]

Originally Posted by flatford8

I like that relay method.....a lot better than my “backyard” switch idea.....if you come up with that eBay link to the 5-pack of those relays, I’d like to get some....thanks.....Mark

They were on amazon from a company called Irhapsody 5 pin relays.