I have a 1991 Mazda BG and have lost the remote

You can't, because the vehicle has an alarm and engine immobilizer that are all computer controlled by ECM, BCM and anti-theft module..

When the car was new, it came with 2 operational keys and 1 Valet key. The idea is that when you lose key 2, or you buy a car with one key, you have another made. You need an auto-locksmith for two new keys and programming.

The only mentions of hotwiring are people here on Fixya.

https://www.google.com/search?q=1998+Mazda+Soho+121%2C+1.3.How+to+bypass+ignition

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You can't bypass an immobilizer as it is all computer controlled and monitors the security modules. You have to fix the issue not find a way around it.

https://www.google.com/search?q=mobile+auto+electrician+near+me

Immobilizer System

mazdabg.com https://www.mazdabg.com > CT-L1007_en PDF The PATS (Passive Anti-Theft System) is an immobilizer system that has been developed by Ford and used for the first time by Mazda in 1996 for the 121 (ZQ).
70 pages

How to reset immobilizer on 323 Mazda 1998?

JustAnswer https://www.justanswer.com > Car Questions
May 28, 2014 - Turn key 1 to LOCK and wait for 5 minutes until security light decrease in flashing frequency to 1.2 seconds. 3. Input code word. 4. Observe ...
1 answer · Top answer: My name is XXXXX XXXXX I am a professional here at Just Answer/Pearl. I noticed that your ...

SOLVED: How to reset anti theft in mazda b3000.

Fixya https://www.fixya.com > ... > Cars & Trucks > Mazda
Nov 29, 2020 - You can also to reset the anti theft in a mazda b3000, try disconnecting the battery for around 10 minutes.

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  mazda security reset Questions & Answers (with Pictures)

  https://www.fixya.com > ... > mazda security reset
  ...mazda b3000 security light blinking engine wont start \ You can put it on standby mode by holding the alarm reset button down while turning the key back & ...
  
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fob doesnt control immobilizer key has security set up --fob is designed to open and lock doors and reset alarm ---and no bypass to immobilizer

vague info --generic answer --should be able to operate vehicle with the key and order a new fob cheap online --and no bypass for immobilizer

Probably best to get the immobilizer unit, cpu, key and switch from a doner vehicle from the junk yard or on ebay, make sure you dont need the transmission cpu as well. This is a quick fix I have done myself.

If you have the manual there should be a fault tree code to fix your problem.

I show immobilizers where only started in the 1998 accords, if you have a remote starter and they used a key in the box bypass all you need to do is find the box under the dash open it up and use the key

An immobilizer bypass is an electrical circuit which allows current to flow to whatever component is starved of current to keep the engine from running (usually the coil). The immobilizer opens the circuit to the coil, the immobilizer bypass closes the circuit to the coil.

If you didn't install an immobilizer circuit, then you don't need the bypass. There are probably instructions you missed in the manual explaining the immobilizer circuit.